Jig and Fixture Design: A Treatise Covering the ... - Forgotten Books

J I G A N D F I XT

DES IG N A S

G TH E PR I N CIPLE S O F J I G AN D F I XT U R E D E S I GN TH E I M P O RTAN T CO NSTR U C TI O NA L D E TAI L S AN D M AN Y DI F F ER E N T TY P E S O F WO R K H O L D I NG D E VI C E S U S E D I N I NTER C HANG E AB L E M AN U F A C TU RE V

A T R E TI E C O E R I N

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E D ITE D B Y

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ON E S F RA N KL N D ASS OCI ATE E DITOR O F MA H IN ERY P LA NING A ND M I LL ING OF T U RNING A ND B ORING M EC H A NI S M S A ND M EC H A NIC AL M O V E M ENT S ET C T H RE A D-C U TTING M ET H OD S !

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F I RS T E DI TI ON

N EW YO RK

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IN DU S TRI AL PR E S S MA CH I N E RY P U B L I S H IN G C O

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C OP YR I G H T ,

1 9 20

BY

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ND USTRI AL P RES S N E W Y O RK

C O O S IT ON A ND MP

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ECTROT ING YP

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P L I MP I O N ’

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PREF A CE

The d e ve lopm ent of machin e too l s has be en accompani ed by a corresponding development of auxi lia ry equipment for in creasing the quan t ity an d imp roving the quali ty of the products of thes e machi n e s Wh en eve r dupli cate parts requi re som e op e ratio n such as dri l ling planing or mill ing the s elect io n of a suitable typ e of machi ne i s oft en followed by th e d e sign of wha tever speci al tools or attach me nt s are need e d to adap t t h e machi ne to the operatio n requi red The tool gui di ng a n d w ork holdin g jigs and fix t ures whi ch are n ow used in prac ti cally all machi n e sho p s r ep res en t t h e most imp ortan t class of sp eci a l equipm ent an d thi s b o ok d e al s exclusively wi th t h ei r d e sign a n d construc tion A s most j i gs are used for dri ll in g o p erat i o n s a book was p r e vi ously publ i shed en tit led D ril li ng P racti ce a n d Jig D e covering di fferent types of dri llin g machi n es a n d the ir s i gn us e the d e sign of drill jigs and t o som e extent the desi gn o f fix t ures such for example as are used o n m illing machi ne s Wh il e the subjec t s of dri ll ing a n d j i g d e sign are closely allied it i s no longer p ossible t o cove r t h e m both in a s ingle volume owing to th e extensive cha n ges i n dri lling practi ce and the increas ing use of jigs and fixtures of various types on different c lasses of machi n e t ools Therefor e the book referred to has b ee n r ep lace d b y two volum e s of which thi s is one The other “ book M odern D rilli n g P racti ce i s already well known to many designers s hop foremen and machini st s in terested in the latest types of drilling mach ines an d their u se Thi s new book Jig and F ixture D e si gn contains that p art of the volume o n D ri lling P ractice and fig D e sign which dealt wi th j igs an d fixtures Thi s mate ri al was used because it i s a trea ti se o n the princip l e s of j ig an d fix tur e des i gn which contains informa ti o n that i s indi sp en sab l e in a book of thi s .

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PRE F A CE kind

Thes e original chapters whi ch explain the general pro c e d ur e i n de s igni ng jigs and fixtures and how work s hould be located clamp e d have b e e n supplemented by a large amoun t of n ew matter thus making the present book unu sually compl e te A gr e a t variety of jig and fixture de signs hav e been des cribed and illustrated in order to S how j u s t how the principle s and important d e tail s referred to in the forepart of the book are applied under many di fferent con di tion s a n d to j igs and fixtures u s e d o n vari ou s type s of machine tools M os t of the designs illu s trated in thi s book have be e n sent to M A CHINE R Y from men i n the machin e bui ldi ng field b e cause th e designs w e re considered unusual and worth p lacing o n re cord While it would not b e po ssibl e to giv e credi t to each indivi dual contributor we are indebted to all who have assisted i ndi rectly in p reparing thi s treati s e and especially to E inar M orin and A lbert A D owd recognized too l experts and p roduct i on engine e rs who have supp li ed valuable material for several o f the chapt e rs on jig des i gn .

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TH E E DI TO R

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CO N T EN T S C

HAP TE R I

P R IN C I P L E S

D E I G S G N J

I D iff e ence between Jigs O bj ect s of Jig and F i xtu e and F ixture F undamental P rin iple of Jig D e ign C lamping D evic Locating P oint Weight of Jig Jig provided with F eet Material fo Jigs Gene al S umma y of P rinciple of Jig R ema k on Jig D e ign D e ign Type of Jig Open Jig B x Jigs De tail of Jig D e ign OF

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JI GS D a ing e igning pen Jig Imp o ing the O v D w Jig P S imple F o m of Jig by Adding L ocating S c ew and F eet f the Jig Example of Open v id ing C lamp D ill Jig O P E N D R I LL

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CH AP TE R III C L O S E D O R B OX J I G I B Jig Gene al P ocedu e in the D e ign of C lo ed Jig f Rapid P o d uction Special F eatu e of B x Jig Example of C lo ed or B x Jig

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IV N G I B U S H I S G J Mate ial f Jig B ushing R emovable B u hing Mi cellaneou D imen ion of S tationa y Jig B u hing Typ e of Jig B u hing Mean f P eventing L oo e D imen ion of R emo vable B u h B u hing f om Tu ning ing S ew B u hing S pe ial D e ign of Gui de B u h ing Met hod of making Jig B u hing Ha dening Jig G ind ing and L apping B u hings C H AP TE R

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PAGES

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LO CATIN G P OI N T S AN D A B L E STO PS P ins

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and S top u ed a L ocating Mean L ocating by Mean of V block C up and C one L ocating P oint S ew B u hing and S lidi ng B u hing u ed as L ocating — Mean Adj u table L ocating P oint Special Type of Adj u table S top L ocating f om F ini hed Hole — L at ing by K eyway in the Wo k C ommon D efect in i D e ign Jg s

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HAP TE R VI I D E LA M P I V I S G G E C N C J Type s of C lamp H ook bolt S c ew tightening D e S winging L eave Tape Gib vice E Wedge ent ic Clamping A angement Application to Jig D e ign

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HAPTE R VII E XA M P L E S O F D RILL J I G D E S I GN — —hole D iff e ent Type of Indexing Jig f D eep o Jig D illing - Jig of S imple D e ign for drilli ng S traight and D ill Jig equipped with Mill ing A ttach Angula Hole ment Jig for C os d illing P i ton and F acing W i t pin B o e Unive al Jig Machine Vi es with D rill Jig Attachment Miscellaneou D e ign

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HAP TE R VIII B ORI N G JI G S B oring Jig of S imple D e ign A dj ustable B o ing Jig — B o ing Jig supported on Wo k Jig de igned f S up po ting B a on On S ide of Hole Only Jig f Multiple B oring C ombination D rill and B o ing Jig

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MILLIN G AN D PLAN I N G F IXTURE S F ixtu e f milling to a Given L ength Duplex F ix ture Adj u table F ix tu e for Angular Work F ixtu e a ranged fo Lateral and Angula Adj u tment Indexing Milling F ixture Variou D e ign of Radial Milling — Example of P lane F ixtu e D e ign F ixtu e

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C H AP TE R X

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IXTURE S F O R TURRET LATHE S A N D VE RTI C A L B O RI N G MILL S Impo tant P oint in the D e ign Adju table F ixtu e f Holdi ng C a ting of D iffe ent Diamete Adj u table B lank P ovi ion f F ixture for S pecial B evel Gea maintaining Accu acy in Adj u table F ixtu e Va iou D e ign of Adj u table F ixture fo V e tical B oring Mill s F

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H A TE R XI TH E F L O ATIN G P R IN C IP L E A S APP LI E D TO F IXTUR E WO R K Impo tant P oint in the Application of F loating P in iple — D ill Jig f P i ton D ill Jig with F loating C lamp D ill Jig with F loating B u hing and Rough C olla Milling F i tu e with F loating Clamp Locating V ee and L ocato Va iou othe D e ign of L o ating D evi e illu t ating the Application of the F loating P inciple C

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HA P TE R XI I APP LI C ATION O F TH E TH RE E P OIN T P RIN C I P LE I N F IXTU R E S h D v Three point L ocating and Clamping e ice T ree point S uppo t for F lywheel F ixtu e Th ee point F ixtu e C

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on a Hub Ca ting F i tu e having Th ee C lamp ing Jaw and Three L ocating P ad Double Th ee point L ocating D evice s

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HAP TER XIII SP E CIAL J I G AN D F IXTU RE M E CHAN I S M S E qualiz ing the P e u e of C lamping D v e C lamp s that d aw the Wo k down F irmly on t h L ocating Mean Multiple-Clamping D evice C lamping D evice f F ixtu e t hat do not inte fe e wi t h the Tool u ed Three-point Clamping D evice

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HAP TE R XIV P ROVI DIN G F O R U P KE E P I N DE S I GN IN G JI GS A N D F IXTU RE S P oints P ertaining to Upkeep D ill Jig f a R eceive D illing and R eaming Jig Inde ing F i tu e F o ging f a Clutch Gear F i tu e with In e ted J aw B evel F ixtu e for a Gea F i tu e wi t h A dj u stable F eatu e s Hub Ca sting

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F I XT U R E

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C HAP TE R

PRIN CIPLE S

DES I G N

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J I G D E S IG N

OF

Jigs and fix tures may be defined as devices used in the manu

facture of duplicate parts of machines and intended to mak e pos sible interchangeable work at a reduced co s t as compared wi th the co s t of producing each machine detail individually Jigs and fixtures serve the purpo s e of holding and properly locat ing a piece of work whi le machined and are pro vided with ne ce s s ary appliances for gui di ng supporting setting and gaging the tool s in such a manner that all the work produced in the s ame jig or fixture will be al ke i n all re spects e ven with the employ ment of un ski lled labor When u sing the expre s ion ali ke it implies of cour e simply that the pieces wi ll be near enough alike for the purpo s e s for which the work being machined i s intended Thu s for certain cla s ses of work wider limits of variation will be permi ssible without affecting the proper u se of the piece machined while in other cas e s the limits of varia “ tion wi ll be s o small as to make the expre ssion perfectly alike li terally true O b j e ct s of Jig s and F ixt ur e s The main ob j ect of using J gS an d fix ture s i s the reducti on of the cost of machines or machine detail s made in great numbers Thi reduction of co s t i s ob t ai n e d in con sequence of the increased rapidity with which the machines may be built and the employment of cheap er labor which i s po ssible when using tools for interchangeable manu fa c t u ri ng A nother object not le s s important i the accuracy with which the work can be produced making it po ssible to as s emble the piece s produced in jigs wi thout any great amount of fitting in the a ss embling dep artment thu s also eff ecting a great saving in this respect The u se of j igs and fixture s practically doe s away wi th th e fitting as th i s expre s si on was unders tood in the old -tim e shop ; i t elimi nates c u t and try methods and do e s ,

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D E SI GN

JI G

away wi th call e d patch work in the p roducti on of machin ery It mak e s i t possible to have all the machines built in the S hop accordi ng to the drawings a thi ng which is rather d i fficult to do if each individual machi ne i n a large lot i s built without reference to the other machine s in the same lot The interchangeability obtain e d by the use of j gs an d fix tures makes it als o an easy matter to quickly replace broken or worn out parts withou t great additional cost and trouble When machi ne s are built on the individual plan it i s nece ss ary to fit the part replacing the broken or worn out piece in place involv ing considerable extra expen s e not to mention the delay and the di fficultie s occasi oned thereby A s mentioned jigs and fixtures permit the employment of practi cally unskilled labor There are many operations in the building of a machine whi ch if each machi ne were built in di vi dually without the u s e of special tool s would require the work of expert machini s ts and toolmakers S pecial tools in the form of jigs and fixture s permit equally good or in s ome ca s e s e ve n better re sults to be O btained by a much cheap er class of labor p ro vi ded the jigs and fixture s are prop erly de signed and cor A no ther po ssibili ty for s aving particularly in the re c t ly made ca s e of drill and boring jigs pro vided with guide bushings in th e same plane i s met wi th in the fact that such j igs are adapted to be used in multiple spindle drills thereby s till more increasing the rapidity wi th whi ch the work may be produced In shops where a great many duplicate parts are made containi ng a number of drilled hole s multiple spindle drills of complicated design which may be rather expensiv e as regards firs t cost are really cheaper by far than ordinary simple drill pre ss e s A nother advantage which has been gained by the u s e of J l gS an d fixtures and which should not be lo s t S ight of i n the enu me ra ti on of the points i n favor of building machinery by the use of special tool s is that the details O PE machine that h as be en provided wi th a complete equipment of accurate and durable j igs and fixture s can all b e fini shed simultaneou sly in differen t dep artments of a large factory wi thout inconve me nce thu s mak in g it po s sible to as semble the machine a t once after r e ce iving -

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D E SI GN

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the par ts from the di ff erent departm ents ; an d there is n o n eed of waiting for the comp letion of one part into which another is required to fit before making thi s latter part Thi s gain i n time mea n s a great deal in manufacturi ng and was en tirely imp ossible under the O ld ti me sy s tem of machi ne bu i lding whe n each p art had t o b e made in th e order in which it we nt to the fin i sh e d mach ine and e ach consecuti ve par t had to b e l ined up wi th each one of the p revi ously made an d assembled de t ails B rackets bearings etc had to be drill e d i n place often wi th ratchet dri lls which is a slow and always inconveni en t Operation — ifi r n D e e ce b e t w e e n Jig s and F ix t ur e s To exactly define the word j ig as consid e red ap ar t from the word fix ture i s di fficul t as the di ff erence between a jig and a fixture is ofte n time s not very eas y t o decide The word jig is frequently al though incorrectly applied to any kind of a work holdi ng app li ance us e d i n the buildi ng of machi nery the same as in s ome S ho p s the word fixture i s appli ed to all kinds of sp eci al tools As a g eneral rule however a jig i s a special tool which whi le it holds th e work or i s held o n to the work also contains guides for the resp ecti v e too l s to be used ; whereas a fixture is only holdi ng the work while the cutting tools are p erforming the op er ation on the p i ece without contain ing any special arrangements for gu i di ng these t ools The fix ture therefore mu s t its elf b e securely held or fixed to the machine on which the operation i s performed ; hence the name A fixture however may s ometimes be provi ded with a number of gages and s tops although it does n ot con t ai n any sp ec i al de vices for the guiding of the tools Th e defini ti on given in a general way would therefore Cla s s ify j i gs as s pec i al tools u s ed particularly in dri ll i ng and boring operations whi le fixture s in particular would be tho s e special tools used on milli ng machi ne s and i n some cases on planers S pec i al tool s used on the lathe s hap ers and s lotting machine s may b e either of the nature of J gS or fixtures and sometimes the speci al t ool is actually a combination of both in which case the term drilling fixture boring fixture etc is s uitable B efore enteri ng P ri n c iple s of J i g D e s ign F u nd am e n t al upon a discussion o f the minor details of the de sign of j igs and ,

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D E SI GN

fix tures the fu n damen t al p r in cip les of j i g and fix tur e design wi ll be briefly outlined When ever a jig is mad e f or a compo n ent part of a machine i t i s almost always required that a corre ,

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jig be made up for the place on the machine or other part where the fi st mentioned detail i s to be attached It is of course absolutely necessary that the s e two jigs be p erfectly alike as to the location of guides and gage p oints In order to have the hole s and guides in the two j igs in alignment it is ad vi s able and almo s t always Ch e aper and qu i cker to transfer the holes or the gage points from the first j ig made to the other In many in s tances it is p ossible to use the same jig for both part s C a s es where the one or th e oth e r o f these pr i nciples i s applicable will be shown in the followi ng chap ters i n the d et ai l e d d e scrip tion s of drill and boring jigs There are s ome cases where i t i s not advi sable t o make two one for each of th e two p arts which are to fit together It S J g may be impo s sible to properly locate the j i g on on e of the parts to be dr i lled or i f the jig were made i t may be so compli cated that i t would not be economical U nder such con di tions the comp onent part itself may be use d as a jig and the respe ct ive holes in thi s part used as guides for the tools when machi ning the machine detai ls in to whi ch it fits Gu i de bu shi ngs for the drills and boring bars may th e n be p laced in the holes in the comp onent part itself In many ca s e s drilling and boring opera ti ons are al s o done to great advantage by u sing the brackets and bear ings al r eady asse mb le d and fastene d to the machi n e body as guide s One of the most i mp orta n t quest i o n s t o be dec i ded before mak i ng a jig i s the amount of money whi ch can be exp ended on a special tool for the O perati on requ i re d In many cases it i s po ssible to get a h i ghly effici ent tool by aki ng it more compli cat e d and more expen s i v e whereas a le s s e ffi cient tool may be produced at very small expense To decide whi ch of the s e two types of jigs and fixtures s hould be de signed i n each in di vi dual ca se depends enti rely upo n the ci rcumstances There S hould be a careful comparison of the present co s t of carryi ng out a certain operation the expe ct e d cost of carrying out the sam e operati o n sp Ond ing

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wi th an efficien t tool an d th e cost of bu i l di n g tha t tool it se lf U nl e s s thi s i s don e it i s likely that the sho p i s burde n ed wi th a gr e at numb e r of special tool s and fixtures which while they may b e ve ry useful for the production of the parts for whi ch the y ar e intended a ctually involv e a loss It i s readily s ee n how uneconom i cal it would be to ake an expen si ve jig and fixtur e for a machine or a part of a machine that would only have to be duplicated a few time s In s ome cases of course there may be a gain in using special device s in order to get extremel y g ood and accurate re sults L o cati n g P oin t s The mos t imp or t ant requ i rements in the design of jigs ar e that good facili ti es be p rovi ded for locatin g th e work and that th e piece to b e machined may be easily i ns e rted and qu i ckly taken out of the jig so that no time is wasted in placi ng the work in position on the machi ne performing the work In s ome cases a longer time is required for locating and d amp ing the p i ece to be worked u p on t han is requ i red for the actual machi ne O p eration i tself In all such cases the machi ne p er forming the work i s actually i dle th e greater part of the time and ’ added to th e loss of the operator s time i s the increa s ed expens e for machi n e cost i ncurred by such a condition F or thi s reason the locating and clamping of the work in place quickly and accurately should be carefully s tudied by the designer befor e any attempt i s made to de sign the tool In choosing the lo cat ing surface or poi nts of the pi ece or part consideration must b e g i ve n to the facili ti es for locati ng the corresponding p art of th e machine i n a simi lar manner It i s hi ghly impor t an t tha t thi s be done as otherwise although the j i gs may be alike as f ar as thei r guiding app liances are concerned there may be no faci li ty for locatin g th e corresponding p art in the same mann e r as th e one already dri lled and whi le the holes drilled may coi nci de oth e r surfaces also required to co i ncide may be con siderably out of line O ne of the main pri nciple s of locati on therefor e i s that two comp onen t p arts of th e machi n e should b e locat e d from correspondi ng poi nts a n d surfac e s If possible sp e ci al arrangements should be made i n the d e sign o f th e j i g so that it i s i mpo ssible to ins e rt th e pie ce in any bu t ,

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JI G

6

D E SI GN

t h e corr e c t w ay M i s t ak e s are ofte n mad e o n t h i s account in S hops wh e re a great deal of ch e ap help is us e d p i eces being p laced in jigs upside down or i n some way other than the cor rect one and work that has been previ ously machi n e d at the expendi ture of a great deal of time i s entirely spoiled There f ore whenever p ossi ble a j i g should be made fool-proof When the work to b e machi ned var i es i n S hape and s ize as for in stance i n th e cas e of rou gh castings it i s necessary t o hav e at least some of the locating points adj ustable and placed so .

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that they can be ea sily reached for adjustment but at the same time S O fa s tened that they are to a certain extent po si tive In the following chapters different kinds o f adjus t able locati n g points will be described in detail D e s ing vi c e The strapp i ng or clam pi ng arra n g e me nt s Cl am p should b e as simple as po ssible without sacrificing effectivenes s and the strength of the clamp s should be such as to not only hold the pi ece fi rmly i n place but also to take the strain of th e cutting “ t ools without springing or givi ng When de signi n g the jig th e di rec ti on in which the strai n of the tool or cutters acts upon the work should always be con si dered and th e clamps so placed t ha t they wi ll have the hi gh e st degr ee of str e ngth t o resi st th e p ressure of the cu t The mai n principles i n the applicati on of clamps t o a j g or fixture are that they S hould be conveni ent for the operator quickly op erated and when detached from the work still con n e c t e d w i th the j I g or fixture i tse lf so as to p reven t the o p er ator from losi ng them M any a time looki ng for lost strap s Clamp s screws etc cau s es more delay in S hops than the extra cost incurred in designi ng a jig or fixtur e somewhat more com p li cat e d i n order to make the bin di ng arrangement an i ntegral p art of the fix ture i tself G reat complication i n the clamping arrang em ents how eve r i s not advi s able U sually clamping arran gements of thi s ki nd work well when th e fixture i s new but as the v arious par t s become worn compli cated arrangements are more likely to get out of order and the extra cost incurred in rep ai ri ng often outwe i ghs the tem p orary gain i n qu i ckn ess o f operation ,

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D E SI GN

J IG

7

The judgmen t of the d e signer is in every cas e th e m o s t im portant po i nt in th e desi gn of jig s and fixtures D e finite rules for all cases cannot be given General principles can b e s tudi ed but th e efficie ncy of the i ndivi dual tool wi ll dep end entirely up on the judgmen t of the tool designer i n app lyi ng the genera l p rin c ip le s of tool de s ign to t h e case i n ha n d When designing th e jig or fix tur e the l ocati ng and b e ari ng p o in ts for the work a n d the loca ti o n of the clamp s must also be so s e l e cted that there is as li ttle li abi lity as po s sible of sp ringi n g th e p i ece or jig or both out of shape when app lyin g th e Clamp s Th e sp ri nging of ei ther the o n e or the other part wi ll cause in corr e ct results as th e work surfac e s wi ll b e ou t of align men t wi th the hol e s drilled or the faces mi ll e d Th e clamps or s t rap s should therefore as far as po s sible be so placed that t hey ar e exactly o pp osite some bearin g po i nt or surface on the work The designer must use hi s judgment i n re W e igh t of Jig s gard to the amoun t of metal p ut into the jig or fixture It i s des i rable to make these tools as li ght as pos sible i n order that they may b e eas i ly handled be of smaller S ize and cos t less i n regard to the amount of materi al used for the i r making but at the same t ime i t is p oor economy to sacrifice an y of the ri gi di ty and stiff ne s s of the t ool as thi s i s o n e of the main consi derati ons in obtainin g efficient results On large s ized j igs and fixtures i t i s possible t o cor e out the m et al in a number of places withou t decreas in g i n th e least the s treng th of the j ig itself Th e corners of j IgS and fix tures should a lways b e we ll round e d and all burrs and S harp edge s fil e d off so as to make th em co nveni en t and pl e asan t for handlin g Smalle r j igs shou l d also b e mad e with handles in prop er places so tha t they may be held i n posi tion while working as in the case o f dri lling j igs and also for conveni en c e in moving the jig abou t Jig s P r ovi d e d wi t h F e e t O rd i nary dri l l j Igs should al ways be p rovi d e d wi th fe e t or legs o n all S i des which are oppo site the holes for the bushing s so that the jig can be p laced level on th e t able of th e machine Th e se feet also grea t ly faci li ta t e th e making of th e j i g making it e asi er t o lay ou t and plane the differ en t fi ni sh e d sur fac e s O n t h e s i des of th e j ig wh e r e n o feet are ,

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J I G DE SI GN

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r e qui r e d if the body i s made from a cas ti ng it i s of advantage to have small p rojec ti ng lugs for bearin g surfaces when laying ou t and p laning Whi le jigs are mo s t commonly p rovi d e d wi th four feet on each si de i n some cases it is su fficie n t to provide the tool wi th only three f e e t bu t care S hould b e tak en in either case tha t all bu shi ngs an d p laces wher e p res sure will be appli ed t o the tool ar e p laced i nsid e of the g eom et ri cal figure obtai n e d by con n e c t ing by lin es the p o in ts O f loca ti o n for t he fee t While it may seem that three f eet are p referab l e t o us e b e caus e the jig will the n alway s obtain a bearing on all th e three feet whi ch i t would n o t wi th four feet if the tabl e of the machin e were no t absolutely p lane i t i s not qu i te saf e t o us e the smal le r number of supp orts because a chi p or some other obj e c t i s li able to come under one foot and thr ow the jig and th e p iece ou t of line wi thout thi s bein g noti c e d by th e opera tor I f the same thi n g happens to a jig wi th four fee t it will rock and invari ab l y cause the op erator to n o ti ce th e defect If th e tabl e i s out of true th i s defect too wi ll be n oti ced for the same reaso n feet are generally cast sol i d w i th the jig frame he n t h e W Ji g frame is made from machine st e el and somet i m e s in the case I j g of cast i ro n Jl gS detachable feet are used O pinion s di ffer as to th e relat i ve meri ts M at e ri al s for Ji gs o f cast i ron and s t e e l as materials from whi ch to cons truct the i and fixture bodies The d e c i sion o n th s poin t sh o uld depend I j g t o a great exte n t upon the usage to which the fixture i s t o b e put an d the character o f the work whi ch i t i s to han dle F or small and m e dium sized work s uch as typ ewri ter se wing machi ne gu n add ing machi ne cash re gi ster p honograp h a n d similar p arts t h e st e el jig offers deci d e d advan t ag e s but for larger work such as tha t encoun t ered in automobile engine an d machi n e tool fixture s the cast i ron jig is undoubtedly the cheaper and more advi sable to use The steel jig should be left so f t in order that a t any fu ture ti me addi ti onal hol es may be added or the exi s ti n g bushi ngs ch ange d as r e qui red Wi t h a cast i ron j ig thi s addi ng of bushi n gs i s a di fficul t mat te r as th e fram e i s usually bossed “ spot fini shed at the point wh e r e the bushi ngs ar e located and an d i t is very di fficult to build up o n the jig fram e i n ord e r to ,

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IO

D E S I GN

lai n lugs proj e c ting ou t i n the sam e p lane as the bo ttom of the jig or lugs with a slot in them to fit the body of T-bol ts are the common means for Clamping fixtures to the table F or bori ng jigs it is u nn ece ss ary to p rovi de more than thre e such Clamping points as a greater number is likely to cause some springing action in the fixture A slight springing eff ect is almos t unavoidable no matter how strong an d heavy the jig i s but by properly applying the clamp s it is p ossi bl e to confine thi s sp ring ing within commercial li mits Jigs should always be tested before th e y ar e us e d so as t o make sure that the gu i di ng provi sion s are placed in the right relati on to the locating p oin ts and in proper relatio n t o e ach other mary of P rin c ipl e s of Jig D e s ign S ummariz i ng th e S um principles referred to the following rules may be given as the main po i nts to be consi dered in the desi gni n g of jigs and fixtures B efore plann i ng the de sign o f a tool compare the cost of p roducti on o f the work wi th p r e sent tools wi th the exp ected cost of producti on usi ng th e tool to be made an d see that the cost o f bu i ldi ng i s not i n excess of expected ga in B efore laying out t h e j i g or fixtur e d e c i d e u p o n th e lo ca t 2 ing po in ts a n d outli ne a clamp in g arran gemen t M ak e a ll d am pi n g and b i nd i ng dev i c e s qu i ck act i n g as 3 as p ossi bl e 4 In s e lecti ng locati ng po ints s ee t hat two compon en t par t s of a machin e can be loca ted from correspondi ng points and sur faces r ake the fool proof that i s arrange i t so that th e M j g 5 work cann ot be inserted except in the correct way 6 F o r rough castings make some of the locati ng p o i nts adjustable L s ocate clamps that they w i ll be i n t he be t p osit i o n to S O 7 re sist the pre s sure of th e cutti ng tool when at work 8 M ake i f possi ble all clamp s i ntegral p arts of t he j l g or fix ture A h i c void compl i cated clam pi g arra gemen t w h n n s are 9 liable to w e ar or get ou t O f o rd e r P

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D E S I GN

I J G

1 1

lace all clamps as ne arly as po ssible opp osit e some bearing poin t of the work to avoid springin g C ore out all u nn ecessary m e tal makin g the t ools as l ight as possible consisten t wi th rigidity an d stiffness R ound all corners 2 P rovi de handles wher ever thes e will make th e handl in g 3 of the j ig more conveni ent P rovi de feet preferably four opp osite all surfac e s con 4 taining guide bushings in drilling and boring j i g s P i lace all bush ngs inside of the geometrical fi gure form e d 5 by connectin g the points of location of the feet 6 P rovi d e abu n dant clearanc e particularly for rough castings M ake if possible all locati ng points vi sible to th e op erator 7 when pl acing the work in position 8 P rovi de hole s or escap e s for the chips P ro vide clamping lugs located so as to preven t sp ring 9 i n g of the fixture on all tool s which mu s t be held to the ta ble of the machine while in u se and tongues for the slots in th e t abl e s i n all mi l ling and planing fixtures 20 B efore using in the shop for commerc i al purp oses te st all j igs as soon as mad e Typ e s of Jig s Th e two principa l class e s of J l gS are drill I l S a n d bori n g s F i x t ures may be grou p ed as m i lling j g j g pla n ing and sp lining fixtures although there are a number of special fixtur e s whi ch could n ot be classifi e d under any special h ead D rill j i gs ar e i n t ended exclusi vely for drilling r e aming tap pin g a n d facing Whene ver the s e four operations are re quired o n a piece of work it is as a rule p ossible to pro vide the ne ce s sary arrangements for performin g all th e se op e rations in one an d t he same jig S ometimes separat e j igs are made for each one o f these operation s but i t is doub tless more conveni e n t and cheaper to have o n e jig do for all as the de sign of the j ig will not be much more complicated Although it may be p os sible to make a di s tinction between a number of di fferen t type s of drill j ig s it is almost impossible to defin e and to get proper IO

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I J G

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DE S I GN

n ames for t h e vari ous class e s owin g t o th e gr e at vari ety of shap e s of the work to b e drilled There are however two general typ e s that are most commo nly us e d the di fferen ce between them being very marked The s e types may be classified as or box j i gs S omet im e s the open j i gs ope n j i gs and close d j i gs are call e d clampi ng j i gs The open jigs usually have all the drill bu shings in the same plane p aralle l wi t h o ne another and are n ot provi ded wi th loose or r emo vable walls or leave s thereby making it possible to ins e rt the piece to be drilled without any mani pulation of the parts of the jig The s e jigs are often of ,

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such a con s truction that they are applied to the work to be dri ll e d the jig bein g plac e d on th e work rather than the work b eing placed in the jig The j ig may be held to the work by straps bolts or clamps but in many cases the j ig fit s into or over som e fini shed part of the work a n d in thi s way the jig is locat e d a n d h eld i n posi ti on Th e cl osed drill jigs or box j i gs fr e qu entl y resemble s ome form of a box an d are in tend e d for pieces where the holes are to be dri ll e d at vari ous angles to one anoth e r A s a rule the p ie ce t o b e drilled can be in s ert e d in th e jig only aft e r one or more l e aves or covers have be en swung out of the way S ome t im e s it is n e c e ssary to r emov e a loose wall whi ch is held by bolts a n d dowel p in s in order to locate the piece in the j ig The work in the clo s e d drill jig may be held in place by s e t scr ews scr ew bushings straps or hook bolts The combin atio n dril lin g and boring j ig i s another typ e of cl osed jig designed to s e rve both for dril ling and boring opera ti ons B efor e designing a combination drill and boring jig the re l atio n between and numb e r of the drill ed an d bor e d holes must be tak en in to con sideration and also th e s ize of the piece to be machi n ed In case there i s a great number of hole s it may be of advantage to have two or e ven more jigs for the same p ie c e b e caus e it mak e s it easier to d e si gn an d make the jig and very likely wil l give a bett e r result The hole s drille d or bore d in the first j ig may b e used as a mean s for locating the piece in the jigs used lat e r o n C ombin ation drill an d boring j igs ar e not very w e ll adapted for pieces of larg e siz e ,

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I G J

D E S I GN

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3

Op e n j l gs of the S imp l e r forms are S imp ly Jigs plate s pro vided with bush e d holes w hi ch are located t o cor respond with the r e quired locations for th e drilled hol e s While holes are sometim e s drilled by firs t laying out the hol e s d irectly upon th e work it is qui te evident that thi s method of dr illin g would not be effici ent i f a large number of duplicate p arts had to be drill e d accurately as there is likely to b e more or l e ss variat ion i n t h e locat i o n of the ho l es and cons i derable l oss of time In the firs t place a cer t ai n amount of t ime is requ i red for laying ou t t h e se hol e s prep aratory to drill ing Th e op e rator O pe n

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Fi g 1 .

J i g for C ylind e r Flange

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Appli c

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ati on

whe n start ing the drill must also be careful to mak e it cut concen tric with th e scrib e d circle whi ch requi re s extra tim e and there will n e cessarily be more or l ess vari ati on To over come these obj e ctions jigs are almost u niversally used for hold in g the work a n d gui ding the drill when dril ling dup l i cate p arts e specially when qui te a large numb e r of duplicate piec e s mu s t be drilled Th e rin g-shap e d j i g shown at A in F ig i s used for drilling th e s tud bolt holes in a cylinder flange an d also for dril lin g the cylinder head whi ch is bolted to the cylin der The positi on of ,

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J IG

4

D E S I GN

wh en the cyl inder flange is being drilled is shown at An an nular projection on the j g fits clo s ely in the cylinder B coun terbore as the illu s tration shows to locate the jig concentric with the bor e A S the holes in the cylinder ar e to be tapped or threaded for s t uds a tap drill which i s smaller in diameter than th e bol t body i s used and th e drill is gui ded by a r e mov abl e bushing b O f t he pro p er size Ji gs of th i s typ e are oft en held in po sit io n by insert ing an accurate l y fitt ing plug through the j g and into th e firs t hol e drilled whi ch p revents the jig from turn in g wi th relat i o n t o th e cylinder whe n dril ling the other hol e s Wh e n th e jig i s used for drilling the head the opp osi t e side i s p laced n ext to the work as S ho wn at C Thi s side has a ci rcular reces s or coun terbore which fits the p rojectio n on the head to p ro p erly locate the j ig A s the holes i n th e h e ad must be slightly l arger in diameter than the studs another sized drill an d a guide bushing of corresp onding size are us e d The cyl i nder is of D i ll J ig f th B Typ F ig 2 course bored and the h e ad turned b e for e the dr ill ing i s done Ji g s of the o p en class as well as thos e of othe r type s are made i n a gr e at vari ety of S hape s an d when in use they are e i th e r appl i ed to the work or the latter is p lac e d in the jig When t h e work i s qui te large the ji g i s frequently p laced on it whereas smal l parts ar e more O ft en held in th e j i g which is so design e d that the work can be clamp ed in the p rop e r position The form of an y jig depends to a great extent on the shape of the work for whi ch i t is intended and also on the location of the hole s to be dri lled A S the number of di ff er ently shaped pieces whi ch go to make up e ve n a single machine is often very th e

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D E S I GN

JIG

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5

great a n d as most parts require more or less drilling j Igs are made in an ahn os t endles s variety of sizes and forms When all the holes to be dril led in a certain part are parallel and e s i a ll e c if they are all in the same plane a ery simple form of v y p jig can ordinarily be used B ox Jig s A great many mach i ne parts must be drilled on different side s and frequently ca s tings or forgings are very irregular in shape so that a j Ig which is made som ewhat in ,

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F ig 3 .

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B ox

J i g for

D illi g B n

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th e form of a box and e nclos e s the work is very ess ential as i t en abl e s the guide bu shin gs to be placed on all sides and also makes i t comparat ively easy to locate and securely clamp the part i n th e pro p er p osi tion for dri l li ng Thi s typ e of jig whi ch becaus e of its form i s kn own as a close d or box j i g i s us ed very exte n sive ly i r t c u a 2 F i i box ji g of s i p l e shown i n Th i s s i n d s e m A p g g lar j ig is used for drilling four small holes i n a part !not shown) whi ch i s located with referenc e to th e gu i d e bushings B by a c en tral pi n A attached to the jig body Th i s p in e nt e rs a hol e in the work which is finished i n another mac hi n e in co nne ct i o n ,

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I J G

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wi th a previous o pe ration A fter the work is inserted in the jig it i s clamped by clo sing the cover C which i s hinged at one end and h as a cam S haped Clampin g latch D at the other that engages a pin E i n the jig body Th e four holes are drilled by pa s sing the drill through the gui de bushi ngs B in the cover A nother jig of the same k ind but d e signed for drilling a hole having two di am e t e rs through the center of a steel ball .

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F ig 4 .

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Jigs for D ri lling P art s h s

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shown in F ig 3 The work which is shown enlarged at A is inser t ed while the co ver is thrown back as indicated by the dotted lin e s The cover is then closed and tightened by the cam latch D and th e large part of the hole is drilled wi th the jig in the po sition shown The j ig is th e n turned over and a smaller drill of the correct siz e is fed through guid e bu shi ng The depth of the large hole could be B on th e O ppo site sid e gaged for each ball drilled by feeding the drill spindle down to a certain position as shown by graduation or oth e r marks bu t .

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D E S I GN

I J G

ings s hould vary the posi ti o n of the clamping bushing could ea sily be Changed The work is properly lo ca te d by th e i n ner en ds of th e thre e guide bu shi ngs a b and e and al s o by th e locating screws l against which th e castin g is held by knurled thumb scr ews m an d n Wh en th e holes a a n d b ar e b e ing drilled th e jig is plac e d wi th th e cove r sid e down as shown at A in F ig 5 and the drill is guid e d by r emovabl e bushings o n e of which is shown at 7 Wh en th e dri lling is completed th e drill bushi ngs are replac e d by reamer bushings and each hole is finish e d by ream ing Th e small hol e 0 F ig 4 is drill e d i n the en d of the cast ing by simply p laci ng the jig o n e nd as shown at B F ig 5 B ox jigs whi ch have to be plac e d in more tha n o n e positio n for drilling the diff erent hol e s are usually pro vi d e d with feet or exte n sions as S hown whi ch are accurat ely fini sh e d to a li gn the guide bu shings prop e rly wi th th e drill Th e s e fe e t exten d b eyond a ny clamping screws bolts or bushings whi ch may p rotrude from th e si de s of th e J l gS and p rovi d e a solid su ppo r t Wh e n in s e rtin g work in a j i g car e should b e t ak en t o r e m o v e all chips whi ch might have fall en u p o n thos e surfac e s a ga in s t which th e work i s clamp e d and which de t ermin e its loca tion S ti ll a n oth e r jig of the box t yp e which is quit e s im i lar t o th e one shown at A F ig 4 but is arran ge d diff e r ently o win g to the shape of th e work an d locati o n of the hol e s i s sh own at B in th e sam e i llustration Th e work has thr e e hol e s in th e base It a n d a hole at i whi ch is at a n an gl e of 5 d egr ee s wi th th e base The three holes are drill e d with th e j ig s tand ing on the opposi t e en d y an d the angular hole is drill e d whi le th e jig r e sts o n the four fe e t k the en ds of whi ch are at such an angl e with th e jig body that the gui de bushi n g for hole i is prop e rly al i gn e d wi th th e drill Th e cast in g is located in thi s j ig by the inner ends of the two guide bushings w an d the bushi ng o and also by two locat in g s crews p a n d a s ide locatin g screw q A djustabl e s crews t and h in the co ver hold th e casting down and it is held laterally by the two knurled thumb screws u and I) If an attempt were made to drill thi s particular par t wi thout a jig !as would be done if only a few castings w e r e ,

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I J G

DE S I GN

19

n eed e d) i t the an gle

would have to be set wi th con siderable care pro vided betw e en hol e i and those in the base had to be at al l accurat e a n d it would be rather diffi cult to drill a n umber of th e s e cast in g s and have th em a ll dupl i cates B y the u e of how eve r designed for drilli n g thi s particular casting a jig t h e relat ive p os i ti ons of th e ho l es in any number of par t s ar e p ract i cally the sam e an d th e work can be done much mor e qui ckly than would be p ossib l e if i t were held to th e dri ll p ress table by ordin ary clamping appli an ces Various desi gns of j i gs wi ll be d e scri b e d in Chapte r VII D e tails of J ig D e s ign The general prin cipl e s o f th e d e sign a n d us e o f jig s have b een exp lai n e d Th e details o f j ig design will now b e con si de r e d Generally sp eaking the most im port ant p ar t s o f a j ig are th e gui de bushi ng s for the dr ills an d oth e r too l s the clamp in g d e vi ces and the l ocating p o in ts against whi ch th e work i s pl ac e d t o in sur e a n accurate p osi t ion in the j ig Th e gui des for th e cutting tools in a drill jig tak e the form o f concen tri c st eel bushing s whi ch ar e pl aced i n t h e ji g body in p ro p er p osi ti o n s The dril l bushings ar e gen e ra lly mad e o f t oo l ste el hard en ed and l appe d a nd where convenien t shoul d b e groun d insi de a n d out Th ey shou l d also b e long enough t o support the dril l o n each si d e r egardless o f the flut ing and they shoul d be so located tha t th e l ower e n d o f th e bushi ngs will s top about th e sam e di stanc e above th e work as th e di am e t e r of the drill Wh e r e ho l e s are S O t h a t Chi p s w ill cl e ar t h e bushi ng s readi l y dr ill e d o n t he s i de o f a co nv ex or a co n cave sur f ace th e e n d of t h e bushi ng mus t be cu t o n a b eve l an d come closer t o the p art be ing drill ed to in sure t h e drill having adequate supp or t whi le s tar ting int o th e work The bushings should have heads o f sufficient diamet e r Lon g bushi ngs should b e reli eve d by in cr e asing t he ho l e d iam e t e r a t the upp er end Th e lowe r end o f the bushi ng S houl d have i ts e dg e s roun ded in order to p ermi t some of th e chi p s be ing shed from the dril l easil y ins te ad of all o f them be ing forced up throu gh the bushi ng It i s also good practi ce to cu t a groove under the head for clearan ce for o m A c s h s wheel when gr i n ng the bu ing on the out ide di h e t ,

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I J G

20

D E S I GN

treat i se covering dimensions and d e si gn i s gi ven in th e “ chapter on Jig B u shings In order to hold the Work ri gi dly in the fig so that it may be held a g ain s t th e locat in g points whil e th e cutting tools o p erate up on th e work j ig s an d fixtures are p rovi ded wi th clamping devi ces S ometi m e s a cl amping devi ce serves the p urp o s e Of holding t h e j ig t o the work in a cas e where the work i s a very large pi ece an d the j ig i s attached to the work in som e sui tabl e w a y Th e p urp o s e of t h e clamp ing de vice however remains the same n ame ly that of prevent ing any sh ifting of the gui ding bu shi ngs whi l e t h e op erat i o n on the work is p erfo rmed The clamping devi c e S hould always be a n in t egral part of th e j i g body in order to p revent i ts g ett ing lost D iff erent typ es o f clamping de vi ces are shown a n d descr i bed “ in the Chap ter o n Ji g C lamp ing D evi ces Th e locat in g po ints may consi st of scr ews pin s fin ished p ads bosses ends of bushin gs seats or lug s cast s olid with t h e fig body e t c Th e vari ous t ype s used are de s cribed i n “ detail in th e ch apter on Lo cati ng P o in ts an d A dju s table S tops '

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CHAP TER

II

DE S IG N O F O PEN D RILL J IG S

To giv e any rational rules or methods for the design of drill j i gs would be almo s t impo sible as almost e very jig must be designed i n a somewhat di fferent way from every other jig to sui t and conform to the requirements of the work All that can be do ne i s to lay down the p rinciple s The main principle s for jigs as well as fixture s were treated at l ength in C hapter I It is p rop osed i n the p resent Chapter to dwell more i n detail o n the carrying out of the actual work of des igni ng ji g s i D B e for e maki n g any attemp t to p u t the lay J g rawings out o f the ji g on p ap er th e design e r should carefully consi der what the jig will be requ ired to do th e limits of accuracy etc and to form in hi s i magination a certain idea of the kind of a ji g tha t would be sui table for the purp o se In doing so if a mode l or samp le o f the work to be made i s at hand it wi ll be found to be a great help t o study the actual model If the draw ing as i s most often the case is the on ly thing that i s at hand then th e outli n e of the work should be drawn in red !or other colored) i nk on the drawi ng paper on whi ch the j ig is sub se quently to be laid out and the jig built up so to speak around thi s ou tlin e The designi n g o f the jig wi ll be greatly simp lified by doi ng thi s as the relation between the work and the jig wi ll always be p lainly before the designer and i t wi ll be more easily deci ded wher e th e locating points and clampin g arrangements may b e p roperly p lac e d Whe n drawi ng and p rojecting the diff e r ent vi ews of the ji g on the p ap er the red outline of t h e work will not in any way i n t erfer e and when the jig is made from the drawi ng the red li nes ar e simply ignored except to the extent to which the outline of the pieces may help the toolmaker to unders tand the drawi n g and the purp o s e of certain locating points and d amp i ng d evic e s s

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JI G

22

D E SI GN

I f po ssib l e the fig S hould b e drawn fu ll size as it i s a great d e al easie r t o ob t ain the correct p rop ortion s wh en so doing O f co urse i n many cases it wi ll b e i mp ossible t o d raw the jigs full size In such cases th e only thing to do i s to draw them to t h e largest po ssible r egular scal e E v e ry j i g draftsman should be supp lied with a se t of bluep rints containi n g di m e nsio ns of standard screws bolts nuts thumb -screws washers wi n g-nu t s slidi ng p oints drills count e rbor e s ream e rs bushings e t c ; i n short with blueprints givin g di mensions of all parts that ar e us e d in the construction of jigs and which are or can be standardiz ed It should be required of every d e si gn e r and draftsman that he use the s e standard s to the larges t p ossibl e ex tent so as to brin g the cost of jigs down to as low a figure as p ossible It is highly desi rable for the obtai ni n g of best resu l t s tha t before s tarting on the drawin g the draft sman who is to lay out the jig should consult the foreman who i s actually going to use the j ig Oftentimes t hi s man wi ll b e able to supp ly the be s t id e a for the makin g o f the j ig or to o l Th e comb i ned exp erienc e of the drafts man an d th e for e man wi l l gen e rally p roduc e a much be t ter tool than could e i ther o f them alon e As a ji g drawing i n most cas e s is only used onc e or a t most only a very f ew times it is not advi s able to make a tracing or bluep rint from the drawin g but as a rule the p encil drawing its elf may be used to advantage If however it i s give n ou t in the shop directly as it come s from the drawing board it is likely to b e come soi led so that after a whi le i t would be impo s sible to make out the meaning of the views shown on it F or this rea s on j ig drawings S hould b e made on heavy paper preferably of brown color whi ch is not as quickly soiled as whi te pap er ; and in order to p revent the drawing from being torn it S hould be mounted on strawboard and held down along the edges by thin wooden strips nailed t o the board It is al s o de sirable t o cover the drawings with a thi n coat of shellac before they are sent out into the shop When thi s i s done dirt and black spots may be washed Off directly ; and the shellac itself may be wa shed O ff by wood alcohol when the drawing i s returned to the draft in g r oo m Th e drawi ng aft e r havi ng b e e n cl e an e d is th en ,

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P N D RI LL J I GS

O E

23

detached from the s t rawboard whi ch may be us e d o ver an d o ver again The drawin g is of course filed away according to the drafting room system The mos t advantageous sizes for jig drawin gs for from medi um to heavy work ar e about as follows : F ull size sh e et 4 0 X 2 7 % in ch e s I H alf size she e t 2 7 % X 0 in ches 2 3 Quarter size she e t 2 0 X 3 % in ch e s E ighth siz e sh eet 1 3 X 1 0 inches 4 Of course the s e sizes will vary in di ff eren t shop s and in many cases p arti cularly when the tool de signing dep artment and the re gular draftin g room are comb i ned as one draftin g dep artment t he j ig drawings s hould be of the same re gular si zes as the ordi n ary machine drawings It is common practice in a grea t many shops t o m ake n o d e t ai l ed drawi ngs oi ji g s but simp ly to draw a su fficient number o f views and sections and to di me n si on th e diff erent p arts dir e ctly on the assembly drawing s In cases wher e the ji g drawing s ar e complicated and wher e th ey are cover e d wi th a larg e number of dimensions which m ake i t hard to read the drawin g and to se e the outlines of the ji g body itself i t h as p roved a gr e a t help to trace the ou tlines of the ji g body and of such p orti on s as are made o f cast i ron o n t racing p ap er omitting all loos e p ar ts and simply p u t ti n g o n the necessary di mensions for m aki ng the p at te rns A blueprint i s then made from thi s pap er trac in g and i s sent to th e p a tte rnmaker who will fin d the drawin g less o f a puzzle and who wi ll need to spen d far l e ss tim e t o un ders t and how the p a ttern actually looks I t i s however go od policy to detai l j ig drawi ng s comp l etely the same as o the r machine de tails Wh en j Igs are mad e for pi ec e s o f w o rk whi ch r e qui re a g rea t many op erations to be carried ou t wi th the sam e j ig an d wher e a great numb e r of di ffere n t bu shings differen t S iz e s o f dri lls reamers counterbores etc are u s ed a sp ecial ope ra ti o n sh e e t should be provided wh ich should be delivered t o the man u sin g the jig together with the jig its elf Thi s enable s him to use the jig to be s t advantage O n thi s sheet should be marked the order i n which the v ariou s operation s are to be performed and th e ,

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JIG

D E SI GN

26

J IG

D E SIGN

with p roper cl e aran c e for the cut ting t ools If th e size a n d l oca tion of the holes to b e dri lled are not very imp ortant as regards accuracy i t is suffici ent to simp ly drill through the work with a full-S iz e d drill guided by the jig plate but when a nice smooth standard sized hole i s requi red the hol e s i n the work mu s t be reamed The hole i s fi rst sp otted by a sp otting dri ll which is of exactly the same siz e as the reamer used for fini shi ng and whi ch ni cely fits the hole i n the ji g p lat e or bushing Then a whi ch is i nch or les s smaller in s o called reamer dr i ll diameter than th e r e am e r i s p u t throu gh leaving only a slight amount of stock for the reamer to remove thereby O btaining a very sati sfactory hol e S ometim e s a sep arat e loose bushi ng is used f or each one of these op erati on s but this is exp ensiv e and also unnecessary as the method described gives equally good results B y usin g th e rose reami ng method very good results wi ll al s o be ob t aine d In thi s case two loose bushi ng s besides the li ni n g bushing wi ll b e use d Th e s e bu shi ngs are d e scribed a n d tabu l a ted in a f ollo wi ng chap ter Th e drill preced ing th e rose chucki n g reamer i s T 3 i nch small e r than the s ize of the hole Thi s dri ll i s fir s t p ut through the work a loose dri ll bu shing made of st e el bein g used for gui di ng the drill Then the rose chucking r e amer is emp loyed u sing i f the hol e in th e jig b e large a loose bushi ng made of cast iron Wh e n di m e nsi o ni n g the fig on th e drawi n g di m e nsi o n s should always be given from two fini shed surfaces of the jig to the center of the holes or at leas t t o the more important ones In re g ard t o th e holes i t i s n o t suffici ent t o give o nly the ri ght an gl e di mensi ons a b c and d e t c F ig 2 bu t the radii between the v ari ous holes must also be given If there are more than two holes th e radi i should always be given between the nearest holes and also betw een th e holes that bear a certain relation to one anoth e r as for i nstance be tween cent e rs of shafts carry i n g meshi ng gears sp rock e ts e t c Thi s will p ro ve a grea t help to the toolmaker In the case under consi deration the di me n s io n s ought to be i en from two fini hed side of the work to v s s g the centers of the hole s and als o the di men sion between the centers of the holes t o be dri lled .

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P N D RI LL JI GS

O E

Wh en using a simp l e

27

made as ou t line d in F igs 2 an d 3 this jig is simply laid down flat o n the work and held agains t i t by a C clamp a wooden clamp or if con veni ent held right o n the drill press table by mean s of a strap or clamp as shown in H e re two pieces of the work are shown beneath the j Ig F ig 4 plate both being drilled at one time Impr ovin g t h e S impl e F ormof Jig Th e first imp rovemen t that could be made on the jig shown in F ig 3 would be the plac i ng of locating poi n ts in the jig plate i n the form of pins as shown in F ig 5 in which the dotted li ne s represent the outline of the work The p lat e n e ed n ot nece s sarily have the shape shown in i j g,

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wi t h L c ting S c w H l ding W k in P l c re

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but may hav e the appearance shown i n F ig 6 according to the conditions The adding of the locating poi nts will of course i ncrease the cost of the jig but the amount of time saved in u sing the jig wi ll undoub t edly make up for the added expense of the jig provided a fair number of piece s is to be drilled ; be side s a great advantage is gained in that the holes will always be located in the same relation to the two side s resting agains t the locating pins on all the piece s drilled The locating pin s are flattened inch from the out s ide circumference and o ff to a depth of TH , dime n sions should be given from the flat to the center O f the pi n

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28

D E SI GN

J IG

hol e s and to th e c ente r of th e n e arest or t h e most i mp or t ant o f the holes to b e drilled in the ji g The same s trapping or d amp i ng arrangements for the jig and work as mention e d for the simpler form of jig may be employed Improving t h e Jig b y Ad d ing Lo cati n g S cr e ws Th e n ext step toward imp roving the ji g under consideration would be to p rovi de the j Ig with locati n g screws as shown in F ig 7 B y the addition of these the locating arrangements of the jig be come complete and the piece of work will be prev ented from These locating screws are placed S hifting or mo ving sideways so that the clamping point s come as nearly Opposite to some bearing points on the work as po ssible In order to p rovide for locating set screws in our pre s ent jig three lugs or projections If po s sible the s e t s crew A are added which hold the set s crews lugs should not reach abov e the su face of the work which s hould rest on the drill pre ss table when drilling the hole s The pre s ent case illu s trates the difficulty of giving exact rules for jig de sign Two s e t s crews are u s ed on the long side of the work but in a ca s e like thi s where the piece i s comparatively short and s tiff one lug and set s crew as indicated by the dotted line s at B in F ig 7 would be fully su fficient The s train of the set s crew placed right between the two locati ng pin s will not be great enough to spring the p i ece out of shape When the work i s long and narrow two se t screw s are required on the long s ide but in the cas e illu s trated two lug s would be con sidered a waste ful de sign Th e means by which Pr ovi d in g Cl amps an d F e e t for th e Jig the work has been clamped or strapped to the j Ig when drilli ng in the drill pre ss !se e F ig 4 ) have not been in tegral part s of the jig in the S imp le typ es shown If clamping arrangements that are integral parts of the jig are to be added the next improv e ment would be to add four leg s in order to rai e the j g plate enough above the surface of the drill pre ss table to get the r e quired space for such clamping arrangements The completed jig of the be s t de sign for rapid mani pulation and duplicate work would then hav e the appearance shown in F ig 8 The j ig here i s provi ded with a handle cast integral with the J l g body and .

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P N D RI LL JI GS

O E

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with

a cl ampin g strap whi ch can be pulled back for r emovin g and inserting the work Instead of having the leg s soli d W l t h the jig as shown in F ig 8 loose legs scr ewed i n p lace ar e some time s used as shown in F ig 9 The s e legs are round an d p rovi ded wi th a S houlder A p r event ing them from screwi ng i nto the j ig p late A headless screw or pin through the edge of the ci rcumference of the thr e ads at the top prevent s the s tuds from becoming loo s e Thes e loose legs are usually made of machine s teel or tool steel the bottom end .

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S t and ar d

J ig

F e et

S c re w s for J ig F e e t

being hardened and then ground and lapp ed so that all four le gs are of the same length It is the practice o f many tool makers n o t t o thread the le g s i nto the jig body bu t S imply to p rov i de a p l ain surface on the end of the le g whi ch enters i nto the ji g p lat e and is driv en into p lace Thi s i s much ea sier, and there i s n o reason why for almost all kin ds of work j i gs p rovi ded wi th l egs attached in this manner should n o t be equally durable fee t are al s o made of the form s hown in the accompanyin g Ji g table where a sep arate s crew is u s ed for hold ing the jig feet to the j ig body When j ig s are made of machine or tool steel and feet are ,

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D E SI GN

P N D RI LL JI GS

O E

31

required th e only way t o p rovid e them i s to in s e rt loos e fee t In the case of cast i ron jig s however s olid legs cast i n p lace are preferable The s oli d legs ca s t in place generally hav e the appear ance shown in the u pper right-hand corner of F ig 8 The two webs of the leg form a ri ght angle which for all practical pur p oses makes the le g fully as s tron g as i f i t were solid The leg is t ap ered 5 degrees as a rule as shown i n the engraving but thi s may b e varied accordin g to conditions The thickne s s of the leg v arie s according to the size of the jig the weight of the work and the pre s su e of the cutting tool s and depend s al s o upon the length of the le g The length b on top is g enerally made one and one half times a A s an indication of the size of the legs required it may be sai d that for smaller jigs up to jig s with a face area of 6 square inches the dimension a may be made from T% to g inch ; for medi um sized jig s to 2 inch ; for larger-sized jig s to % i nch ; but of cour s e these dimen sions are simply i ndications of the required dimen sion s A s to the length of the legs the gov ernin g condition e vidently i s that they mu s t be long enough to reach below the lowe s t part of the work and the clamping arrangement as clearly indicated in the design in F ig 8 If a jig i s to be used i n a mul tip le spindle dri ll i t S hould be de si gned a great deal s tronger than it is ord inarily desi gned when used for drilling one hole at a tim e Thi s i s e sp ecially true i f there is a large number of holes to dri ll simultaneou sly It i s e vide n t that the p ressur e up on the jig in a multip le spindle drill is as many t i me s grea te r than the pressure in a common drill p ress as the number of drills in operation at once R eferr i ng aga i n to F ig 8 a t tention should be called t o the small lugs A on the S ides of the jig body which are cast in place for layin g ou t and p laning p urp oses The h andle should be made about 4 i nche s long which p ermits a fairly good grip by the hand The de sign of the jig shown i simple and fills all requirement s neces s ary for producing work quickly and accu at the same time it i s s trongly and rigidly de signed r at e ly ; Locating points of a di fferent kind from tho s e shown can of course be u s ed ; and the requirement s may be such that adj ust ,

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D E S I GN

I J G

2

able locating point s as d e scribed i n a followi ng chapter may b e requi red A more quick -acting but at the s ame time a far more complicated clamping arrangement might be used bu t th e que s tion is whether the added increa s e in th e rap idi ty of manip u lation offsets the expens e thu s incurred A question whi ch the designer should always ask h i m s elf i s C an more than o n e piece be drilled at one time ? In the present ca se the locating p in s can be made longer or i f there i s a locat ing wall it can be made higher the leg s of the jig can be made longer and the screw holding the clamp can al s o be i ncreas ed in length If th e p iec e s of work are thi ck enou gh se t-screws for ,

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holdi ng th e work agai nst the locating p i n s can be placed in a vertical line or i f the p i eces are narrow they can be placed diagonally so as to gain space If the p i eces are v ery thi n the locating m i ght be a more difficult proposition If they are made of a uniform width they may simply be put i n the slot i n the bottom of the jig as shown in the lower ri ght hand corner of F ig 8 or if a j ig on the p rinciples of th e one shown to the left i u s ed they might be located sideways by a wedge as shown in F ig 0 A couple of lugs A would then be added t o hold the wedge in place and take the thrust In both cases the p i ece s mu s t be pu shed up in place endways by hand If the pieces are not of exactly uniform size and it is desired to drill a numb e r ,

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D E S I GN

J IG

34

Thi s s i d e i s also p rovided with feet and has a fini s hed p ad agains t which the work i s held The locati ng pi ns extend clear through the central p ortion of the j i g body a n d consequently wi ll l ocate t he compon e nt part of the work i n exactly the same p osi ti on as the pi ece of work dri lled on t he f ron t S i de o f the j ig The s ame clamping strap s ar e used the screws be ing simply put i n from t he oppos i te s i de i n t o th e sam e t app ed holes as are used when clampin g on the front s i de of th e j ig The four holes D are gu i de ho les f or drilli n g t h e scr ew h ole s i n the work these being dri ll e d th e body size of th e bolt in on e p art an d t h e t ap dri ll siz e ,

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component part The li ni ng bushing i n the holes D serves as a drill bu shi ng for drilli ng the body size holes The loo s e bu shi ng E F ig is u s ed when drilling the tap holes i n the component p art the in side di ameter of thi s bushi ng bein g the tap drill size and the out ide diam eter a good fi t in the li ning bushi ng The two hole s F F ig are provi ded wi th dri ll bu hi ngs and s erve as guides when drilling the dowel pin hole s whi ch are drilled below s ize leavin g about i nch and are reamed out after the two component parts of the work are p ut together The two holes shown in the middl e of the ji g i n F ig whi ch are provided with lining bu shi ngs and al s o with l oo se bushings as S hown inserted in F ig may be used for .

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t ogether

35

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The larg e b ushi n gs shown be si de th e j Ig i n F ig are the loose bushings shown in p l ac e i n F ig 1 2 It will be no ted tha t the bushi ngs are p rovi ded with dogs for easy removal as ex p la ine d i n a foll ow i ng chap ter A s the central p orti on o f the 11

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body i s rather thi n it wi l l be se e n from F ig 1 2 th a t th e boss e s for t he central holes p rojec t outsi de o f the ji g body i n order to gi v e a long enough beari n g to the bushi ng s Thi s of cours e can be don e o n ly when such a projection doe s no t i nterfere wi th the work The bos s e s i n thi s p articular cas e also s erve another “ purpo s e They make the ji g fool p roof becau e the pieces drilled on th e si de of the j ig shown in F ig canno t be put o n the si de shown in F ig the bo ss e s pre venting the piece from being placed in p o sition in the jig A ttention s hould be called to the s i mplicity of the de sign of thi s jig It simply consi s t s of a ca s t iron plate with fini shed seats and feet projecting far enough to reach below the work l J g

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whe n dri lli ng thre e dowel pins set-scr ews for bri ngi ng the work up a gainst the dowel pins three clamp s and the n e ce ss ary bush in gs The heads of all the set screws and bolts should if possible be made the same siz e so t h a t th e same wrench may be u sed for ti ghtenin g and un s crewing all of them It can al s o be p lainly seen from the halftones that there are no unnecessarily fini shed surfaces on th e j ig a mat t er which i s highly imp ortan t i n e conomical production o f tools Anoth e r example of an Open dri ll J g s i mi l ar i n des i gn to th e o n e jus t described i s shown i n F i The work to be dr i lled g 3 ,

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sho wn at A and B at t he right hand si de of the Jl g In thi s cas e the work is located from th e half circular ends T he pi ece s A and B are comp onen t p arts and when fini shed ar e The p iece A is located again s t three dowe l s cr e wed together pin s and pu s hed against them by s e t -s crews C and held in p osi ti on by three clamp in g strap s as shown i n F ig I 4 In thi s case t he s t rap s are p rovi ded wi th oblo ng s l ots as i ndi ca t ed and whe n the clamp s crews are l oo s ened the clamps ar e simply p ulled backward permittin g the in s erti on and remo val of the work It would improve thi s clamping arrang e Without i nterference ment to place a s ti ff heli cal spr i ng around the screws under each s trap so that the straps would be p reve n ted from falling down t o —

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the bo tt om of th e Jl g when the work was removed At th e sam e time this would p revent th e strap s from swi veli ng around th e screws when not clamp ed In F ig 1 5 t h e p art B i n F ig 3 i s sh own clamp ed i n posi ti o n f or dri lli ng t h e opp os it e s i de of the jig being u s ed for thi s p ur p ose In j i g desig n of thi s ki nd it is nece ss ary to provide som e mean s so t hat the p ar t s A and B wi ll be p laced each on th e corr e c t si de of the jig or as menti oned the jig should be mad e f ool -p roof I n th e p resen t cas e the p ar ts cannot be exchanged and p lac e d o n t h e w ro ng s i d e b e caus e the cov e r or guard B can n o t b e h e l d by th e thr ee strap s shown i n F ig 1 4 as th e screws .

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f or th e s t rap s ar e n o t l o ng en ou g h O n th e other han d th e becau s e i I F pi ec e A could n o t b e p laced o n t h e s i d e shown in g 5 t he l o ng bolt a n d s t rap us e d for clampi ng on t hi s s i de would inte rf er e wi th t h e work It may app ear t o be a fault in d e sign t hat th ree strap s are used t o fas ten th e pie c e A in p lace a n d only one is emp loyed for hold ing pi ece B Thi s differ e nce i n Clampin g arrangement however i s due to the d iff e ren t number and the di fferent s izes of holes t o b e drilled in the di fferent pieces The holes i n the piece A are vier clampin g ar ge r and t he n umber of holes i s greater and a hea l s much as the thru s t o n rra nge m ent i s therefore requ i red i na a ,

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JIG

8 3

the former i s corresp ondingly greater the mul tip l e spindl e dri ll being used for drilling the hole s If each hole were drilled and reamed individually th e design of the ji g could hav e b een com r a t ive ly li ghter a p In the de sign shown the locating of each pie ce ind ivi d ually i n any bu t the right way is al s o taken care of The p iece A whi ch i s S hown in p lace in the j ig F ig 4 cou l d n ot be swung around into ano ther p o siti on because th e s trap and scr ew at E would interf ere F or the same reason th e cov e r or guard B coul d no t be located except i n the right way A s shown in F ig -

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D i ll J i g h w i F i g 3 wi th C t b D i ll d in Pl c 1 5 t h e s t rap and scr e w would have to be de t ached f rom the j 1g i n order to g e t the cov e r i n place if i t w e r e turned around The locating p in s for the work pa ss clear through the body of the jig and are used for locating both p ieces The piece s are located di agonally in the jig becau s e by doing so it i s po ssible to make the outside di m ensions O f the ji g small e r In thi s particular case the p arts are located on the machine t o which they belong i n a di ag onal direction so that the ad di ti onal adv antage i s gai ned of being able to use the same di mensions for locating the jig holes as ar e u s ed on the drawing for the machine details them selves Thi s also tends to eliminate mistakes in making the jigs S o me t imes wh en m o r e o r less c o mplicated mechani sm s ar e F ig

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P N D RILL JI GS

O E

39

comp osed of s everal par ts fitted together and worki ng in relati o n to each other as for in s tance f iction clutche s one jig may be made to s erve for drilling all the individual parts by the addi tio n of a few extra part s applied to the jig when diff erent details of the work are being drilled In F igs 6 7 and 8 such a case i s illu s trated The p ieces A B and C in F ig 6 ar e comp onent p art s of a fri c ti on Clutch and the jig in which these p arts are being drilled is sho wn in the same figure to the left S uppo s e n ow that the friction expansion ring A is to be drill e d The jig i s bor e d ou t to fit the ri ng b e fore it is spl i t an d whe n it i s only ,

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F ri ti on C

rou gh turn ed l e avi ng a c e rta in number Of thousandths o f an i nch for fini shin g The p 1e ce 18 located as S hown in F ig 7 against the steel block D entering into the groove i n the ring and i s then held by three hook -bolts whi ch S imply ar e swung around when the ring i s inserted or removed Th e hook bolts are t ightened by nuts on the back si de of the jig Three holes marked E in F ig 7 are dri lled simultaneou s ly in the multiple spindle dri ll and the fourth hole F !se e F ig 6) i s drilled by turni ng the j g on the side The steel block D F ig 7 i s hard ened and has a hole to guide the drill when pas sing through into the other side of the slot in the ring The block is held in p lac e by two screws and two dowel pins -

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40

Wh e n dri lli n g t h e holes in the lugs in the friction sleev e

B,

the block and the hook bolts are removed It may be menti oned here althou gh it is a small mat t er that these parts s hould be ti ed tog e ther when remov ed and th ere should be a sp ecified p lace wher e all th e p arts belon gin g to a p art i cular jig should be kept wh en not in use The fricti o n sl e ev e B fits over the collar G F ig 1 8 Thi s collar is an ex tra pi ece belong i n g to the jig and used on l y when drillin g the fricti on sl e ev e ; it should be marked Wi th instructi ons for wha t purp ose i t is us e d Th e coll ar G fi t s over the projec ti ng fini shed p ar t H in

F ig

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D ill J i g h w i F ig 6 wi th O f th Pi c i P l c the center of the j i g an d i s l ocated in i ts right p o siti on by the keyways shown Th e keyw ay in the fri c ti on sl e ev e B wh ich must be cut and p lac e d in t h e ri ght rela ti on t o the p rojec ting lugs before the pi ece can b e dri lled l oca t es the sleeve o n th e collar G whi ch i s p rovi ded with a corresp onding keyway A flange on the collar G as shown mor e p lai nly at L in F ig 8 locates the friction sleev e at the right di stance from the botto m of the jig so that the holes wi ll hav e a proper location si deways Two collars G and L are used f or the same pi ece B thi s b ei n g n ecessary because the ho l es M and M in the p rojectin g l ugs shown in F ig 6 are n ot p laced i n the same relation to the side s of the fri ction sleeve The co llars are marked to avo i d mi s takes and corresponding marks on the jig provided so as t o F ig

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42

D E SI GN

It may be well t o add that loose bushings ough t to b e marked wi th the size and kind of cutti ng tool for which they are intended ; and the corre sp on di n g p lace in the jig body where they are to b e used should be marked so tha t the ri ght bushi ng can e asi ly b e p laced i n the ri ght p o si ti o n A few more examples of o p e n dri ll j Ig de sig ns o f vari ous typ es may prove i nstructive In F ig 9 are shown two views of a jig for drilli n g two holes through the ri m of a handwheel To th e l eft i s shown th e j ig it self and t o t h e ri gh t t h e j Ig with th e hand .

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F ig

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19.

D ill r

J i g for

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H

and

wh e e l

wh e e l mounted i n place ready for dril ling As shown th e han d wheel i s locat ed on a s tud through i ts bore and clamp ed to the ji g by passin g a bolt through the stud thi s bolt bei ng p rovi ded with a spli t wash e r o n the end The spli t washer p ermits th e easy remov al of the handwheel when drilled and the p uttin g i n p lace o f an o ther handwheel wi thout l o s s o f time Th e hand wheel i s loca t ed by two set screws B passing through two lugs p rojecting on each side of a spoke in the handwheel the s e t screws B holding the handwhe e l i n p o si ti on whi le bei n g dri lled by clampin g agai n s t th e si d e s of the spok e The jig i s f astened on the edge of the dri ll press table i n a manner simi lar t o tha t in di cated i n the i llustration so that the table does not i nterfer e .

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P N D RILL JI GS

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43

wi th the wheel The vertical hole with the drill guided by bu shi ng G is now dri lled i n all the handwheel s thi s hole being drilled i nto a lug in the sp oke held by the two set screws B When thi s hole i s drilled th e jig i s mov ed over to a h orizontal drillin g machine and the hole D i s drilled i n all the handwheel s the jig being clamp ed to th e t abl e of thi s machi n e i n a manner s i mi lar t o tha t o n t h e dri ll p r e ss .

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D ill J g I n F ig 2 0 a t A an op en dri ll p g of a typ e si mi lar to tho s e shown in F ig s 1 1 and I 3 i s sh own Thi s j ig howev er i s pro n A w i th a b l ock locatin g arrangement objectionable V vi d e d f ea ture of this j i g i s that the one clamping strap i s placed in the cen ter o f the piece to be drilled S hould thi s piece be slender it may caus e it t o be nd as there i s no bear i ng surface under the F ig

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D E SI GN

work at the p lace where the clamp i s located for taking the thrust of the clamping pre sure A t B and C in the same illu s tration are S hown the front and back vi ews of a dri ll jig where the front side B is u s ed for dri ll ing a small p iece located and held in the jig as u sual ; and the back side C whi ch is not provi ded wi th f eet i s located and app li ed d irectly on the work i tself i n the place where the loose p i ece i s to be fastened the work i n thi s ca s e bein g s o large that i t sup p ort s th e ji g instead of the j ig supp orti ng the work A t D i n the same illu s tration is s hown a jig for locatin g work by means of a ton gue E Thi s tongue fits into a corresp ondin g slot in the work Thi s mean s for locating the work was referred to more completely in connec t i on with locating devi ces F inally at F is s hown a jig where the work i s located by a s lot G i n the jig body i nto whi ch a corre sponding tongue i n the work fits ,

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C H AP TE R II I

L

D E S IG N O F

C O S ED O R B o x

J IG S

In the preceding chapter the s ubject of the de si gn of o pen drill jigs h as been dealt with In the pre s ent Chapter i t is p ro posed to outli ne the develop ment of the design of clo s ed or box jigs A ss ume that the holes i n a p iece o f work as shown i n F ig are to be drilled H oles A are drilled straight through th e work while hole s B and C are so call e d blind hole s drilled in to the work from the opp osite sides AS thes e hole s mu s t no t be drilled t h rou gh it is e vident that the work must be drilled from two si des and the guiding bushing s for the two b lind ho l es mu s t be p ut i n O pposite sides of the j ig The simple s t form of jig for thi s work is shown in F ig 2 Th e pi ece of work D i s located be tween the two p lates E whi ch form the jig and whi ch if the jig i s small are made of machine steel and ca s ehardened If the jig is large these p lates ar e made of ca s t iron The work D i s si mp ly located by the outline s of the p lates which are made t o t he same dimensions as r eg ards wi dth as the work it s elf The p lates are held in posi ti on in relati on to each other by the gui di ng dowel pins F The s e pins are dri ven into the lower p la te and ha ve a sliding fit in the up per one In some ca s es blocks o r lu g s on one p late would be used t o fit i n to a s lot i n the other p late instead of p i ns These minor chang es of course d ep end u p on the nature of the work the princip le i nvolved being tha t some means mu s t be p rovi ded to p revent the two plates from shifting in relation to each other whi le drilling The whol e de vi ce is finally held tog e t her by clamp s of suitable form The hole s A may be drilled from either s i de of the jig as they p as s Clear through the work and the guide s for the drill s for the s e holes may therefore be placed i n either plate Oppo site the bu shings in either plate a hole i s drilled i n the other p lat e ,

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46

JIG

D E SI GN

for Cl e aranc e for the dril l whe n p assing throu gh an d for th e e s cape of the chi ps The two plates should be marked with neces s ary general in formation regarding the tool to be u s ed the po sition of the plates etc to prev ent mi s take s by the op erator It i s al s o an ad van tage not to say a nece ssity to use some kind of connection b e tween the plates in order to avoid such mistakes as for instance the placing of the upper plate in a revers ed po sition the wr ong pins entering into the dowel pin holes This of course would locat e the hole s in a faulty po sition B e sides if the upper plate be entirely loo s e from the lower it is likely to drop off when the jig is stor e d and get lost S ome means of holdi ng the two p arts ,

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D ill d r

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when not in u se or when not cl amped down on the work should therefore be provided S uch a means i s em ploye d in F ig 2 where the screw G enters into the guiding dowel pin at the left and holds the upper plate in place A p in H fitting into an elonga t ed slot i n the dowel pin as shown at the left could also be u s ed in s tead of the screw The design shown pre s e nts the v ery simplest form of box j ig consi s ting as it does of only two plate s for holding the neces s ary guiding arrange ments and two pin s or oth e r means for locating the p lates in r elation to each other In manufacturing wher e a gr e a t number of duplica t e parts would be encountered a j ig designed in the simpl e man ne r shown in F ig would how ev e r b e wholly i n ad e qua t e T h e simple st ,

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form o f a j 1g t ha t would be used in such a case would be one in which some ki nd of locating mean s is employed as in di cated in F i g 3 where three pin s are pro vided two along the s ide of the work and one for the end of the work again s t which the work ,

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may be pushed prior to the clamping together of the two j g plates In thi s illustration the jig bu shings are not shown in the el evation and end view i n order to avoid confusion of line s Th e next improvement to which thi s j g would be subjected would i

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o ati ng

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ad

d d e

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b e the addin g of walls at the end of the j g and the screwing together of the upp e r and lower plate the result being a j ig as shown in F ig 4 Thi s design presents a more advanced s tyle of clos e d j 1g a typ e which could be recommended for manufac turin g purp oses Whi le the same fundamental principle s ar e -

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J IG

4g

still i n evi denc e t hi s j g embodies most of th e requ i r e me nt s nece ssary for rapid work This de sign provide s for integral clamp ing means within the jig it s elf provided in this cas e by the s crews J The upp er plate K i s fa s tened to the walls of the lower plate L by four or more screws M and two dowel pins N The cover K could also be p ut on as shown in F ig 5 by making the two part s a good fit at 0 one piece being tongued into the other Thi s giv e s greater rigi di ty to the J g In this jig also solid locating lugs F are u s ed in s tead of p in s R eferring again to F i g 4 by p ro vi di ng a swi nging arm P wi th a set screw Q the work can be taken out and can be i n s e rted I

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J i g S u i t ab l e for

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os e s

from the s i de O f the j i g which will save making any provi si ons for taking off or putting on the top cov er for every piece being drilled If there i s enough clearance between the top cover and the piece being drilled the screw Q could of cour s e be moun t e d in a s oli d lug but it would not be advantageous to have so large a space between the top plate and the work as the drill would hav e to extend unguided for some di s tance before i t would reach the work The set screws Q and U hold the work against the locating points and the set screws J on the top of the j g pre vi o u sly referred to hold the work down on the fini s hed pad R on the bottom plate The s e s crews al s o tak e the thrust when the hole C i s drilled from the bottom side It i s immaterial on which side the bushings for guiding the drills for the two holes A are p laced but by p laci ng them in the cover rath e r than in ,

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of cours e dep en ds enti rely up on the si z e o f th e work an d the size of the hole s to be drilled S ometimes one set s crew i s quite suffici ent whi ch in thi s ca s e would be placed in the ce n ter as i ndicated by the dotted line s in F i g 4 The type of jig s hown in F ig 7 now po s sesses all the features ,

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F ig 6 .

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J ig in F ig

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wi t h Tw

u s d i n Comb i n

ati on

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generally required for a good j i g and pre s ents a type which i s largely u s ed in manufacturing plant s particularly for medi um and heavy work The jig s hown in F ig 8 howev er repre sents another typ e s omewhat different from th e ji g i n F ig 7 The ,

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J i g i m pr ove d b y

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Ad di g F D ill B u hi

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s wh i ch for composed of two large eparate piece s j large jigs means two s eparate cas tings inv olving s ome extra exp en s e i n the pat t ern shop and foundry The reas on for mak ing the j ig in two parts i n s tead O f ca s ting it in one i s becau s e it makes it more conv enient when machining the jig The loc at Ig

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F ig 7 .

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ing p o int s how e v e r are som ewha t hi dde n from view when the p iece is in s erted The jig shown in F i g 8 consi s ts of only on e casting L p rovided with feet and resemble s an open dri ll ji g The work is located i n a manner similar to that already d e scribed and the leaf D wi de enough t o take in all t h e bu s hings except t he one for the hole that must be drilled from the op po site side ,

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is fitted acro ss the jig and gi ven a good bearing between the lugs in the jig wall It swings around the pi n E and is held down by the eye bolt F wi th a nut and washe r S ometimes a wing n u t i s handi er than a hexa g on nut C ar e should be taken tha t .

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Fi g 8 .

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Alt

e rnati ve

D

e s i gn

of

J ig in F i g 7 .

the feet reach below the top of the nut and screw The se t screw G holds the work down and takes the thru s t when the hole from the bot t om side is drilled The three holes A A and B are drilled from the top so that the t hru s t of the drilling of these three holes will be taken by the bottom of the J g body L If one s e t screw G is not suffici ent for holding the work in place the leaf may b e made wider so as to accommodate ore binding screws It i s howev er an objectionable feature to place the Clamping screws in t h e b u shing plate If the leaf has not a perfect fit in t s e ts and on the swiv e ling pin the screw will i lt the l eaf a its s .

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one way or another an d thus caus e the bus hin gs to stan d at an angle with the work p roduci ng faulty results I n order to avoid thi s O bjectionable feature a further improvement on the jig i ndi cated i n F ig 9 is p rop osed I n the jig body the loca ting points and the set-screws which hold the work against the loc at i ng pin s are p laced so that they wi l l not i nterfere with two straps G which are provi ded with elongated s lo t s and hold the work securely in place al s o su s taining the thrust from the cutting tools The s e strap s should be heavily de signed in order to be able to take the thru s t o f the multiple sp indle drill becau s e in thi s ca s e all the bushin g s excep t the one for hol e B are placed ,

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mp

ng O

p

i

e r at o n s

s

i n the bottom o f th e j Ig body The l ea f i s made n arrower an d i s not as heavy as the one S hown in F ig 8 because it does not i n thi s ca s e take any thru s t when drilling and simply serve s the p urp ose of holding the bu shing for hole B The leaves and loose bu shing plates for jigs of this kin d are generally made of machine steel but for larger sized jigs they may be made of cas t i ron The l e af i n F ig 9 is s imp ly held down b y the thumb -s crew H I f the hole B comes near to one wall of the jig it may not be nece ss ary to hav e a l eaf but the ji g casting may be made with .

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a projecting lug D as shown in F ig 0 the jig otherwise being of the same type as the one illus trated in F ig 9 Th e proj ecting ,

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p ar t D F ig 1 0 i s s t r en gthened wh e n n e cessary by a rib E as indi ca te d C ar e must b e tak e n that th e r e i s suffici ent clearance for t h e pi ece to b e ins erted and removed O nce in a whil e it happ ens eve n wi th fai rly good jig de signers that an otherwi s e well designed jig wi th good locating clampin g a n d guiding arrangements i s render e d useless for the S imple r e aso n that there i s not enough Clearance t o allow the in s ertion of the work F ig 1 1 shows the same jig as before but with the addi ti o n al feature of p ermi tting a hole in the work to be drilled from the end a n d si de as indi cated th e bushi ngs E an d F being added .

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for this purp ose The bu shi n gs i n this case extend through the jig wall for some di stan c e in order to guide the drill closely to t he work B osses may also b e cas t o n the jig body as in di cated by the do t t e d lin es to gi v e a longer bearing for the bu shi ngs F eet or lu g s are cast a n d fi ni sh e d o n t he S i d e s of the ji g o pp osite the bushi ngs so tha t the j ig can b e p laced co nveniently o n the drill-p ress table for dril li n g i n any di rection When drilling the holes from th e bushin g s E an d F the thru s t i s taken by the stati on ary locati ng pin s I t i s obj e cti onable to use set screws to take the thrust although in some cases it i s necessary to do so W h en de igni ng a j i g o f thi s typ e care must be taken that strapping arran gem en t s and loca t i ng points are placed so tha t ,

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they i n no way will i nterfere with the cuttin g too l s or guidi n g means In this case the strap H is moved over to one side in order to giv e room for the bu shings F and the s e t -screw K S trap G should then be mo v ed al s o because mo ving the two strap s in oppo site direction s still gives them a balanced clamping acti on on the work If the s trap G had been left in p lace with the strap H moved sideway s ther e would have b een some t en d e ncy to tilt the work S ometime s one hole i n t h e work comes at an angle with th e face s of the work I n such a cas e the ji g mu s t be made alon g ,

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J i g for

D illi r

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H ol e s f m

T wo

ro

D i ct i re

on s

the line s i ndi ca t ed in F ig 1 2 the fee t on the si des op posi t e t o where the drill bushi ngs are placed being planed so that their face s will b e perp endi cular to the axis through the hole A Thi s will in no way interfere with the drilling of hole s whi ch are p erpen di cular to the faces of t he work as these can be dr illed from the opp osite side o f the work th e ji g then resting on the feet B S hould i t however be necessary to drill one hole at an angle and oth e r holes perp endi cular to the face of the work from the same si de an arrangement as shown in F ig 3 would be used The jig here i s made i n the sam e manner as the jig S hown in F i g wi th the diff erence that a bu s hing A is placed at the required angle It wi ll be seen how ever that as th e .

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55

o ther holes drilled from the same side mu s t be drilled p e rp e ndi cu la ly to the face s of the work it would not b e of advantage to p lane the feet so that the hole A could be dri lled i n the manner previou s ly hown in F ig Therefore the feet are left to sui t the perpen d i cular hole s and the s eparate ba s e bracket B F ig i i s used to hold the n the de i red incl i n e d pos i t i on when s j g 3 the hole A i drilled It S tand B in F ig 3 i s v ery uitable for thi s special work i made u p as li ght as possible being cored a t the center so as to remov e superfluou s metal The s e stands are sometimes p ro r

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D ill i g H l t A gl vi d e d wi th a clamp ing dev i ce for holdin g t h e fig t o th e stand S p e ci al stands are not only used for d illing hole at an g le s with th e r e mai n in g holes to be drilled but s ometi m e s such stands ar e made t o su i t the jig i n cases where i t would be inconvenient t o p rovi de the ji g wi th feet fini shed bo ss e s or lug s f or resting di rectly on th e drill p ress table Wh en a j ig of larg e dimen sion s i s to be turned ov er either for the in s e rtio n or removal of the work or for drilling hole s from opp osi te s i de s i t is i n case s where the use of a crane or hoi s t can be obtained very sati factory to have a special devi ce at t a h e d to the jig for tur ni ng it over F ig 4 s how s s uch an arrangemen t In thi s i llu s trati on A repre s ent s the jig wh ich is F ig

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be turne d ove r The two studs B ar e dri ve n in to th e Jl g in convenient places as nearly as p ossible in line with a gravity axi s These stud s then re s t i n the yoke C whi ch i s lifted by th e crane h ook placed at D The jig when li fted off the table can then ea sily be swun g aroun d T h e yoke i s made simply of round machi ne s teel .

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F ig

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Jig

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an d

S t and for

D ic ev

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for T

D illi r

H ole s

ng

u

r ni n g ove r

H y Ji g e av

an d

at an

H

an d

A

ngl e

ling

s

xampl e s of Cl o s e d or B ox Jig s T he d e ve l op men t o f a clo s ed or box jig has now been treated In the following pages a numb e r of example s of closed jig desi gn s will b e shown and de s cri bed There i s however no di stinct di vi sio n li ne between op en and clo s ed drill jigs s o that in many ca s e s it 15 rat her in con si stent to attempt to make any such di s ti ncti on E

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The swingin g strap I wh ich really is the only thi n g tha t makes thi s j ig a clo s ed jig s erv e s the s ole purp ose of taking th e thrust of the heav y cutting tool s when drilling the hole E and of steady ing the work when facing off the two ends of the hub The two collar head screws K hold the strap t o the ji g body and the se t ,

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Pl d El ti f J ig S h w i Fig 5 screw L bears again s t the work This strap is easily swu n g out of the way by looseni ng one of the bollar-head screws a s lot be ing mi ll e d at one end of the strap to permi t this S tati onary bu sh i ngs are u s ed for the s crew hole and dowel holes but for the bear i ng hole E three loo s e bu shing s and a lining bu shi n g are e mploy e d F ig

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an an

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J I GS

59

The hole E i s first O pen ed up by a small twist drill whi ch make s the work con siderably easier for the s -ca lled ro s e bit drill The latter drill leaves T g inch of stock for the ro s e reamer to remov e whi ch p roduces a very smooth s traight and concentric hole The la s t operation is the facing of the h ole s The holes ju s t drilled are now use d to guide the pilot s of the facing tools and as the operatio n is p erformed whi le the work i s held in the jig it i s imp ortant that th e l ocati n g or s t rappin g arrangement s should not be in the way In connection with the openi ng up of a hole with a smallc r drill it may be mentioned that it is not only for la ge hole s that t his method of procedure wi ll save time but the method is often a time saving one al s o for smaller holes down t o i i nch i n di ameter when drilled i n steel The u se of lubrication in jigs is a v ery i mportant i tem the mo s t common lubricant being Oil or va s eline but soap solution is al s o used The objection to the latter i s that unle ss the machi ne and tools are carefully cleaned i t i likely to cause ru s ting U si ng a lubri cant freely wi ll s av e the guiding arrangements such as the drill bu shi ngs th e p ilot s on counterbore s etc to a great extent The jig in F ig 5 is shown in F ig 6 and a clear idea of the design of the jig will b e had by s tudying this line engraving The bracket B in F ig 5 could hav e been drilled in a di ff erent way than de s cribed whi ch would s ometime s be advantageous It could be held in a chuck and the hole E reamed and faced in a lathe whi ch would in sure that t h e hole would be perfectlycentral wi th the outside o f the bo ss Then a jig could be de signed locatin g the work by a s tud enterin g i n hole E as indi cated in add i tional dowel pin s and s t screws being used for F ig 7 locating the piece sidewi e The whole arrangement could be held down to the table by a strap and bolt a jack scr ew supp ort i ng i t at the o v erhan ging end F ig 8 s how s another jig of the closed t yp e wi th the work i n serted The piece A i s a ca sing and the hole s to be drilled vary greatly in size The casing re s ts on the flat fini hed bottom surface of the jig and i brought up s quarely again s t a fini hed p ad at B It further locate s again s t the fini shed lug C in order ,

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to in sur e g e t ting th e prop er amou n t of m et al arou n d th e hole D A t the bottom it i s located against the s liding point E the latter being adju s table because the location of the work is determined by the other locating points and surface s The work i s held again s t the locating point s by the long e t s crew s hown to the left Thi s clamping arrangement howev er is not to be r e com mended becau s e thi s screw mu s t be s crewed back a considerable di s tance in order to permit in s ertion and remov al of the work .

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W

OR

DRI LL RE SS TA LE D ill ing B ck t h wn n B d in t h L th -P

F ig

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17.

S

i m pl P l t ft H l e

a

er

a e

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J i g for

K

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B

ra

E h as b e e

e

or e

s

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a

in F ig

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15,

e

eye bolt u s ed in the manner de s cribed in a precedi ng chapter would have giv en better service The three s trap s G hold the work again s t the bottom s urface and the two s trap s H hold it against the fini shed surface at B There i s not a long finished hole through the ca s ting as would be a ssumed f oni i t s appear ance but simply a short bearing at each end the remaining part of the hole being cored out F o thi ea s on the hole i s drilled and reamed in tead of being bored out the latter operation

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wou l d b e a s l ow e r o ne A lthough th e two short bearin gs ar e som ewha t far ap ar t th e gu i di n g bushi ngs come so clo s e to thes e beari n g s that the ali gnmen t can be made very good The screw holes an d dowel p in holes at the bottom of the ca si ng are no t shown i n the i llustrati on as the inserted casing i s n ot ye t dri lled The hole dri ll ed from bushing I i s a rath e r imp or t ant hole and the bushi ng r e quire s a long beari n g i n order to guide the drills s traight wh en drilling W hen thi s j i g was made the p rojectin g lug which was p rovi ded s olid with the j ig body to gi v e a bearing .

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Fig

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B ox

J i g for

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as i ng

d ill d f om F i v r

e

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e

D i cti re

ons

th e j i g bu s hing came so much ou t of th e way in th e rough castin g for the ji g that ha lf of the li ni n g bushi n g would have bee n exp osed It was therefore planed off and a bushi ng o f the type shown in F ig 5 in the Chap ter on J ig B ush ings i nsert e d i n s t ead i n order to p rovi d e for a l ong beari ng L eaf K wh i ch c ar ri e s the bushi ng s for drilling the hole D fits in to a s lot planed out in the jig body and is h e ld down by the eye -bolt L Two lugs M are provided on the main ca tin g for hold ing th e pin on whi ch the leaf s wi vels A rou n d the hole to

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D E SI GN

th er e are thr ee small t ap ho le s 0 whi ch ar e dri ll e d b y th e guidi ng aff orded by t h e bushing P which is mad e of cast i ron and provided wi th s mall steel bu shing s placed in side as illustrat ed In the bu shing P i n F ig 4 in the Chapter o n J ig B u hi ng s i s another hole Q which fits o ver a p i n located in the top of the leaf and which in sure s tha t the three screw hole s will come in It should be n oted that larg e p orti ons of th e t h e right po sition

D

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19.

B ox

J i g for

D illi r

ng

W or k

s

h wn o

by

D h-d as

ott e

d

Li

ne s

body ar e c or e d o u t a t t op an d bo tt om in ord e r t o mak e it light and easy to handle O f cour s e some metal i s al s o s aved by the con s truction of j gs in thi s manner but comparing the p ic e of cast iron with th e total price of a finished jig of thi s typ e the saving in this re spect is o in significant that it i s not worth whil e mentioning The leaf K i s al o made of cast i ron being o f l J g

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p articularly l ar ge size and i t a bearing on the ji g body ,

JI

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63

is planed at the places where it has

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hows a Closed j g about which there can be no doub t but that it should be cla ssified as a box j i g The p i e c e of work drilled the foot trip A has two holes B and C whi ch ar e drilled i n thi s jig Th e cyli ndri cal hub of the work i s l o ca te d agains t V blocks and h e l d in p l ace by a swi n gi n g strap D Th e work i s s further located again t a stop p i n placed opposi t e the set-screw E The trip i s located si dewi s e by being brought again s t anoth e r F ig

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J i g sh own i n

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1 53

s top b y th e s et scr ew F One -quar te r o f a turn o f the collar-he ad scr ew o n the top o f the jig releases the swinging strap -which is then turned out of the way ; thi s permit s the trip to be removed H s e t s crews and another to be in s e r t ed alf a turn or less of the i s e nou gh to rel e as e and clamp the work agains t the stop s men t i one d A l i ne engrav i ng o f t his jig i s shown in F ig 9 which gives a b e tter i dea of some of the detail s of the con truction In F igs and 2 are shown two views of another type of The work A to be drilled is shown at the left c lo s ed drill j g -

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2

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64

JIG

in

D E SI GN

both illu s trations and consi t s of a special lathe apron with large bearing hole s screw hole s and dowel pin holes to be drilled The apron i s located in the ji g body in the s ame mann er as i t is located on the lathe carriage in this case by a ton gu e whi ch may be seen at B in F i g 2 2 Thi s t on gu e fits into the s lot C i n the jig s

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Fi g

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2 1.

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F ig

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a

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er

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an d

of

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for

wh i c h

J ig in F ig

.

it i s U s e d

21

care being taken in the con s truction of the j i g that the s lot i s made dee p enough to p revent the tongue from bearing in th e bottom of the slo t A good s oli d bearin g should be provided however for the finished surface on both side s of the tongue The s urface D should al so hav e a solid bearing on the surface E i n t h e jig the difference in heigh t between the two beari ng sur faces in the jig being exactly the s ame as between the two bear i ng surfaces on the lathe carriage where the lathe apro n i s to b e fi tted The work i s brought up against and further located by ,

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66

J IG

D E SI GN

t o make i t as l i ght as p ossi bl e to handl e Lu g s p roject wher ev er n ecessary to gi v e amp le beari n gs t o t he lini n g bushi ngs and in turn to the loo se guidi n g bu shing s F ig 2 3 s hows two clo s ed jig s made u p o f t wo ma i n parts wh i ch .

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planed and as embled by s crews and dowels as indicated the rea son for making the j igs in this way bein g the ea s e of planing the bottom s ection The work drilled i n the s e jigs some special slide s i s located by the dov etail and held up agains t one dov e t ail S ide by set screws A as s hown in the illu s tration In th e jig '

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to

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the left th e work is located endwi se agai nst a dowel pi n and i s held up against thi s stop by a set-screw through the block shown to the left Thi s bloc k mu s t be taken out when the slide i s in th is being the reas on why a lu g ca s t directly in place se t e d through which the set s crew could pass i s not u s ed The top p late D i s held down on the mai n body by S ix fillis t e head s crews N o clamp ing E and two do wel pin s F pre vent it from shi fting arrangements except the set screws A are nece s s ary The holes bei n g drilled from the top the main body of the jig takes the thrust The s e j igs are als o u s ed in multiple spindle drills O ne ob j ectionable feature of the j ig to the right in F i g 2 3 i s There are th erefore t hat set s cre ws A are diffi cult of acces s ,

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B ox

JI GS

67

ho l es p ie rci n g the h e ads of th e set screws i n two di recti ons in ord e r to allow a pin to be u s e d when tightening the s crews A better idea however is to have the screw heads extend out through the wall and if thi s i s s olid to hav e cored or dri lled holes through which th e h e ads of the s crews may pass In F ig 2 4 i s another Closed dri ll j ig in whi ch the work 8 loca t ed -

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J i g in F i g 2 4 O bl i q u e

25.

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in

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fo r

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J ig

Angl wi t h

D illi B

r

H

ng

l

o es

at

an

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the usua l man n er the j Ig stan di n g on its own feet bu t when dri lling the hole s C whi ch come on an angle the sp ecial stand D is employed which br i ngs the holes i n the right p osition for drilli ng as i llu s trated i n F ig 5 If only the hole s C were to be drill e d the feet on the side opposite the guiding bushings for these holes could hav e been planed off S O that they would have been in a p lane perpendicular to the axi s of the hole s Thi s last j i g has a peculiar appearance on account of the end wall s coming up square as shown i n the illustrations but thi s design was adopted only to simplify matters for the patternmaker i t bein g easi er to make th e p attern this w ay ,

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C H A P TE R I V G B IN G US H I S J

Th e drill s counterbore s reamers etc us e d in Conn e c ti on wi th drill j i gs are guided by st e el bushi ng s whi ch are hardened and ground and p laced i n the jig body in their p roper locati on These bu shings may be of two kind s : s tationary and removable the latter usually being known as loo s e bu shings The mo s t common and the preferable form for the stationary bu shing is shown i n F ig This bushing is straight both on the in side and on the outside excep t that the upp er corners A on the in side are given a liberal radiu s so as to allow the drill to ent e r the hole ea sily while the corners B at the lower end of t he out side are slightly rounded for the p urpose of making i t ea sier t o drive the bu shing into the hole when maki ng the jig and al s o to prevent the sharp corner on the bu shing from cuttin g the metal i n the hole i nto whi ch the bu s hi ng i s driven R e movab l e B u s h i n gs When remo vable bu shi ngs ar e used they S hould never be placed directly in the jig body excep t i f the j i g be used only a few time s but the hole should always be p rovi ded with a li ni ng bushin g Thi s li ni ng bu s hing i s always mad e of the form shown i n F i g If the hol e bored i n the j ig body rece ives the loo se or removable bu shi ng directly the in sertin g and removi n g of the bu shi ng i f the jig i s frequently used would soon wear the wall s of the hole i n the jig body and after a whi le the j i g would have to be rep laced or at lea s t the hole would have to be bored out and a new removable bu shi ng made to fit the larger ized hole In order to o vercome thi s the hole i n the j ig body i s bored out large enough to recei ve the lini ng bushi ng referred to whi ch i s dr iven in place Thi s lini ng bushing then in turn receiv es the loo s e bushi ng the outsi de diameter of which clo s ely fit s the in side di ameter of the li ni ng bushing as shown in F ig 2 i n whi ch A i s the ji g body B the ,

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68

BU

li ni n g

S H I NGS

69

bushi ng and C the loo s e bu shi ng B oth of thes e bush ing s are hardened and ground so that th ey wi ll stand cons t ant u se and wear for som e len g th of t i m e When no r e movabl e bushi ngs are requ i red th e li ni n g bushin g i ts el f becomes th e drill bushi n g or ream e r bushi n g and the i nsi de di ame te r o f the Th e bushi ng lini n g bushi n g will th en fit the cutt ing tool us e d i s cheaper to make and wi ll work fully as well s ho wn i n F i g whe n dri ve n i n place in the hol e r e ce i vi n g i t as do bush in gs havi ng a S houlder at the uppe r en d such as the loo s e bushi ng It was th e p racti ce some years ago to mak e s hown in F i g 2 all bu shi ngs wi th a shoulder bu t t hi s i s unnecessary and simp ly i ncrea s es the cost of making the bu shing B u sh ing s are gen e rall y made o f M at e ri al for J ig B u s hi ngs a good grad e of tool steel to i nsure hardening at a fai r l y low te m pe ra tur e an d t o l e ss en th e dange r o f fi r e cracki n g T hey ,

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F ig

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F ig

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3

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al so b e made from machi ne st e el whi ch wi l l a nswer al l p ractical purp oses pro vided the bushing s are p ro p erly case hardened to a depth of about fi i nch S ometi mes bushi ng s for gui ding tools may be made of cast iron bu t only when the cut ting t ool is of such a design that no cutti n g ed ge s come wi thin t h e bushi n g it s e l f F o r examp l e bushin g s us e d s i mp ly t o su p p or t th e smo o th sur f ace of a boring bar or the shank of a r e amer mi gh t in som e in s t an c e s be made o f cast iron but harde ned ste e l bushi ngs should always b e us e d for gu i di ng drill s re amers tap s e t c wh e n th e cutting e dges Come i n di rect contact with the guidi ng sur f aces I f the out side diameter of the bushing is very large as comp ar e d wi th the di ameter of the cutti ng tool the co s t of th e bushing can som e times be reduced by usin g an out e r cast-i ro n body and inse rting a hardened tool s tee l bush c an

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0 7

ing O ccasi onally i s requ i red as for

D E S I GN

a bushi n g having a larg e outsid e d i ameter example when a large counterbore must be used in a smal l hole whi ch make s i t n e c e ssary t o h ave a larg e O p eni ng i n the jig body D im e n s io ns of Stat io n ary Jig B u s h i n g s S ta n dard d ime n sion s for jig bushings app li cable under all Ci rcumstan c e s can not be given as the s e depend in mo s t cases on the d ifferent conditions of th e various class e s of jigs in whi ch th e bushi ngs are ins e rted The common practice i s to make th e length of th e bushing twi ce the in side diameter of the hole in the bushin g for stationary drill bu shing s On v ery small bushi ngs howeve r say 3; i nch di ameter hole and le ss the length of th e bushin g will hav e to be made longer than twi ce the di amet e r whi l e on very large bushi ngs the length may be made som ewha t l ess than twi c e the diameter Table I give s p rop orti ons o f sta tio nary dri ll bushi ngs The di mensi ons as her e gi ven wi l l be found su i table i n all cases where no speci al condi ti ons d emand devi a ti o n f rom ordi nary p ract i ce If the j ig wal l i s thi n the bush i n g may p roject out as shown in F ig 3 so as to g ive the cu ttin g t oo l th e prope r guiding and support as Close to the work as p o s sibl e In Table II are given di men sions for lini ng bushi ngs not in t en d e d to di rec tly guide the drill but to hold removable bush i n g s whi ch i n t urn gui d e the cu t ti n g tools Th e dim e nsi ons given i n Tabl es I and II are for bushi ngs made from ei th e r t ool s teel or machi n e st ee l Whi le i t i s difficu l t i n some cases to draw a di sti nct line b e twee n s tati onary dri ll bu shings and li ning bushi ngs i t may b e sai d in gene ral that the bushings i n Table I are used for gui d i ng th e dri lls when drilling holes directly eith e r with a full S ized dr i ll whe n th e hole is not required to be very smooth or accurate o r i f greater accuracy is requi red f or guiding a sp ot tin g drill whi ch fit s the bushings exac tly afte r whi ch the hole i s drill ed ou t wi th a s o called reamer dri ll whi ch i s inch or l ess under th e size of the fini shed hol e and fin ally reamed out with a re am e r exactly fitting the hole in the bush ing Th e se bu shings are thus in general u sed when no tapping or counter borin g would be r e qu i red The li ni ng bu sh i n g in Table II .

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B U SH I NGS

7

1

a gain may gu i d e on e of th e tools for the hol e s to b e fini shed directly and then remo vable bushi ngs are i nserte d t o gui de th e other tool s used ll sc e a e u s T f s e o D B Mi n o yp rill us hing s As m enti oned i t was s ome year s ago general practi ce to provi de e ve n stati on ary bushi ngs wi th a shoulder or head as S hown i n bushing C F ig Thi s will p revent the bushi ng f rom b eing pushed through th e j i g by the cutting tool but thi s s e ldom happ ens if th e bu shi ngs are made to fit the tool corr e ctly S ometime s the should e r i s us e d to t ak e the thrus t o f a stop collar which i s ,

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Tab l e I

D im n i e

.

s ons

of

S t ati onary

D i ll B u r

s h ings

clamp e d on the drill to allow it to go down to a certai n depth as shown i n F ig 4 in whi ch C i s the s top collar D t he wall of the jig and E the stationary bushing ; F i s the work In such a case a shoulder on the bu shing should be pro vided If the work to be drilled is located again s t a finished seat or bos s on the wall of the jig and the wall is not thi ck enough to take a bushi ng of standard length then i t is common practice to make a bushing having a long head as shown i n F i g 5 The length A of the head can be extended as far as necessary to get th e prope r beari n g As th e bushing i s driven in p lac e ,

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JI G

2

D E S I GN

and the shoulder of the head bears again s t the fin i shed surface of a bo ss on the j g it will give the cutting tool almo s t as rigid a be aring as if the jig metal surrounded the bu shing all the way up R e mo v ab le bush i ng s are frequently used for work whi ch mu s t be drilled reamed and tapped there then being one bu shing for each of the cutting tool s They are al s o used wh en di fferent pa ts of the same hole a e to be drilled out to di ff erent diam or when the upper portion of the hole i s counterbored e te s 1

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Ta

bl e

II

.

Dim

e n s i on s

of

Lini ng

Bu

s h in

gs

or when a lug h as to be faced o f In thi s ca s e each tool of cour s e h s i t s own guide bu s hi ng The commo n de si gn of remo vable bu shing s i s s hown in F i g 6 The outside i s made to fit the in ide of the lining bu shing with a nice sliding fit so that it can be g ently p re ss ed into the lining bu shi ng by the hand The di s tance A under the head of the bu shing S hould be the s ame length as or longer than the guide bu s hing The thickne ss B of the head varie s of cour s e according to the size of the bushi ng The diameter C of the head should be .

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JIG

74

D ESI GN

but i t do e s n ot add th e co nvenient m e an s fo r r emovi ng th e bushing as do e s the dog To m ake such a bu shing more easily removable the arrangement shown in F i g 8 i s probably the most common A step A is turned down on the head whi ch in thi s case will have to be a trifle larger i n di ameter This step permit s some kind of a tool a s crew driver for i nstance to be put un derneath and with a jerk the bushi ng may be lifted enough t o get a good hold on it The half round slot at B i s milled or filed in t h e periphery of the head and fits over a pin or screw whi ch is fastened i n the ji g body as m e nti on e d b e for e .

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F ig

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M e th

1 1.

od s

us

ed

for P r e ve nti ng

J ig

.

B u hi s

ng s

f m ro

Tur ni ng

I n F ig are shown three method s of holdi ng bushi ngs to p revent them from turni ng the methods all being on the pri n c ip le described : A shows a bu s hi ng ha vi n g a p i n i n s erted wh i ch slip s in a slot cut i n the lining bushi ng ; B show s a bu shi ng h av ing a slot mi lled thr ough the collar a pi n being loca ted i n the ji g to engage thi s slot ; and C i llustrates a more elaborate device that i s someti mes used The stop button which i s fas tened to the j Ig p revents the bushi ng from being drawn out of the liner while wi thdrawin g dri ll s or reamer s as well as p r eventi n g i t from turni ng The following method for holding slip j I g bu shi ngs i n p lac e .

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B U SHI NGS

75

been found to be a very good one : D ri ll and tap a i or inch hole i n the si de of the j ig bu shi ng as indi cated in F i g A fter the bu shing i s hardened and ground screw in a pin and cut it off so that it projects about { inch outside of the bu shing as at B C hip out a S lot in each hole in the jig as indicated at A the hole bein g chi pped in the di recti on of a spi ral B y engagi ng the projecti n g p in in thi s slot the bush ing i s pr evented from turning and from ri sing out of the hole A t the s ame time i t c an ea sily be remo v ed when requi red and there is no pro j ection on the j ig of any ki nd that can be broken off whi le handling It i s not always necessary to tap a hole for the pin i n the jig bu shi ng A p lai n drilled hole i s suffi cient when the bu hing is at least 3 inch thick If the wall of the bu shing i s th inner than thi s the pi n cann ot b e driven i n ti ghtly enou gh to stay in place s ecure ly h as -

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D ill Bu hi g f m Tu ni g D i me n s ion s of R e movab le B u s hings In Table III are give n di men sions for removable bushing s of the type shown in F i g 8 Table I V giv es di men ions for bu shings for holes which are reamed with a ro s e chucking reamer after havi ng first been drilled wi th a dri ll 1 6 i nch smaller than the di ameter o f the reamer wi th which the hole is finally reamed out The bu sh ing to the extreme right o ver the table i the lining bushing which is made of machine steel cas ehardened and gr ound The bushi ng to the extreme left is the bu sh ing for the rose chucking reamer It is made of cast iron and ground The bushing in the center is the drill bu shing whi ch i s made from tool s teel hardened and ground or in case s where it doe s not seem war ranted to make the bushing of tool steel of machine s teel ca se hardened and ground The tapered removabl e bushing shown in F i g 9 is ob j ection F ig

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12

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An t h o

er

M th d f e

o

or

P

r e ve nt i n g

s

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6 7

D E SI GN

J IG

bl e

III

Ta

Wh e n

u

si

ng

d og

s

as

.

illu

D im n i e

st t d i ra e

s ons

n

of

Re

F ig 7 t h e d .

,

D ill B u

m ovabl e

r

im si s i th s en

on

n

s h ing s

l mns

e e co u

are o

mitte d

.

able on account of be i ng expen sive to make an d also on a ccount of being likely to be thrown out of true by chips etc forced in between the outside of the bu s hing and the hole ,

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B U S HI NGS

77

i S ometimes removable bushi ngs are threaded on the out side and made to fit a tapped hole in the jig as shown in F ig The lower part of the bu shi ng i usu ally turned straight ,and ground in order to center the bu shing perfectly in the hole in the jig The head of the bushi ng is either knurled or milled hexagon for a wrench When the s e bushings are u s ed they are as a rule not u sed for the single purpo s e of guidi ng the cutting tool but they combine with this the p urposes of locating and d ampin g th e work F o such S cre w

B us h ngs

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Tab

le

IV

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Bu

s h i ng s

for

H ol e s

me d

Re a

w i th

R o s e Ch

uc king

r

me r s

Re a

8 7

D E S I GN

J IG

purposes they are q uite frequently used Thes e bushings ar e not commonly u s ed as removable bushings as it would take considerable time to un s crew and to again in sert a bu sh ing of thi s type into the j ig body S p e c i al D e s i gn s of G ui d e B u s h i ngs Whe n the gui de bu sh i ng s are very long and con s equently would cause u nnece s sary friction in their contact with the cutting tools they may be rec e ssed as shown in F ig 3 The distance A of the hole in the bu shing is reces s ed enough wi der than the diamet e r of the tool so as not to bear onit Th e length B being about twice the diameter of the hole gives su ffi ciently long guiding su faces for the cutting tool to p r event its fu nning out If the ou t si de diameter of the bush ing is very large comp are d with .

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F ig

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the di ameter of the cutting tool as indicated in F ig 4 the exp ense of making the bush ings may be reduced by making the outside bushing of ca s t i ron in s erting into thi s a hardened tool steel bu shing driven in place The steel bu shi ng is then given di men sion s accordin g to Table I for s tationary bu shings The rea s on why there may be a nece ssi ty of a bushi ng having s o large an outsid e diameter and so small a hole may be that the bu shing is requ i red to be remo ved for counterboring part of the small hole being drilled by a counterbore of large diam eter in whi ch cas e the hole in the jig body has to be large enough to accommodate the large counterbore If a loose or remo vable bushing is longer than the lining bush ing as illustrated i n F ig 5 it wi ll prove advantageous to have the diameter of the pro j ecting portion of the bu shing about 5 7 i nch smaller in diameter than the part of the loo s e bushing which .

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B U SH INGS

79

fits th e li ni ng bushing Thi s le ss ens the amoun t of surface whi ch has to be ground and at the s ame time makes it ea sier to in sert th e bu shing giving it so to s ay a point which will first e nter the lining bus hi ng and it interfere s in no way with the proper quali ties of the bu shing as a gu i de for the cuttin g tool In some case s the holes i n the pi ece to be dri lled are so close to one another that it i s impo ssible to find space for lini ng bushing s in the jig If thi s happen s i t i s neces sary to make a leaf or a loose wall or the whole j ig of machi ne steel or tool s teel hardening a port i on or the whole jig thus made All w nc f G ind ing nd L pping B u h i g T bl V .

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a

O pe ra

A

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insid e

e

o

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a

es

or

D ia me

ti

r

t

a

e r of

s

a

n s

s

s

B u h i n g i n I nc h e

s

on

Gi

r nd

a

o

ut

— B

s id e ;

f t e r g rind ing

Lap

o

u

t s id e

f

g

a ter

ri nd in

g;

C

G

—

r in d

insid e ; D— Lap

.

M eth o d s of M aki ng Jig B u s h ings followed in turning jig bushings

There are se veral method s S ome toolmaker s p refer to chuck out the hole to the desired size and then fini sh the outsi de of the bushing b y placi ng it on an arbor ; others prefer to turn up the bushi n g s two at a time end to end cut them ap art and then bore as the final O peration Thi s i s an excellent method to follow when maki ng large bu shings Th e most rapid method howe ver i s t o chuck out the hole and fini sh the out side a t one s e tt i ng using bar s tock held in the chuck of a rigid e m gine lathe Thi s method is not always practicable on large bu shi ngs In maki ng allowances for grinding and lapping many tool makers u se too s mall limit s whi ch is the cau se of many bu sh ings having to be made over again on account of not finishing out On the other hand many toolmaker s lea v e too liberal an allowance for finishing thereby cau sing unnecessary troubl e .

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and labor The allowance s gl ve n I n Table V can be safely u sed when the bushi ngs are made som ewhere near the propor tion s indicated in Tables I to IV but for extra lon g bushin gs more liberal allowanc e s should be made B efore harde ni ng the bu shi ng s should be p lainly s t amp ed with the size and purpose for which they are intend e d drill é ream etc They should be stamped with a set of plain S harp figures reserved solely for thi s purpose It i s p oor practi ce t o try to stamp the words drill ream e t c in a straight li ne as this is di ffi cult to do If however th e words are lai d out on a slight curve the results are more satisfactory as s light irregularitie s of alignment are not then so noticeable S harp clean figure s and letter s neatly laid out not only improve ’ the appearance of the toolmaker s work but al s o s av e the ’ drilling operator s time as sharp clean cu t figures can be read at a glance H ar d eni n g Jig B u s h ing s Wh en hardeni ng bushi ngs mad e o f tool s teel they should be brought to an eve n red heat in a Cl ean fire ; the heating S hould never b e hurrie d When bush i n gs are heated quickly they are apt to h e a t une ve n ly whi ch r e su l ts in warping or di s t orti on that mak e s i t impos sible to fini sh them to the required size G as furnaces are excellent for h eat ing but a Clean charcoal fire will answer the purpo s e A s soon as the bushing has been brought to an e v en red heat it should be dipped in water ju s t warm enough to take off the Chill The bu shing should then be heated to a sizzling heat after whi ch i t i s left i n th e ai r to cool S ome toolmakers draw bushings to a medi um straw color Thi s i s a m i stake as it onl y tends to shorten their life There are four method s i n common G rin d ing and Lapping L apping wi th a l e ad u se for fini shi ng holes in j I g bushi ng s : L apping wi th a lead lap followed by a cast i ron or lap copper lap 3 Internal gri ndi ng 4 Internal grinding fol lowed by a cast i ron or Copper lap for removi ng the last inch The firs t method is erroneous as it invariably results in bell mouthed hole s e specially when the toolmaker Charge s th e lap whi le in use whi ch i s an unsatisfactory but very commo n .

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th e el e c tr i c furnace ar e di sp l acing em e ry as they cut faster producing excellent results in a comparatively short time as compared to emery N os 90 to 5 are used in connection wi th lead lap s for rou ghin g o p erations F or the final fini shing with cast i ron lap s flour abra sive i s us e d When not in use any abrasive used for lapping should be kept in a co vered box to protect i t from di rt and other foreign sub s tance s A small Chip or p iece o f gr i t will often cu t a dee p score i n a piece of work Lap s should always be run at a fairly l ow sp eed F ifteen to twenty feet surface speed for a l e ad lap used for roughi ng and si ve s ,

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C as t -ir on Lap

to twenty five feet surface spe ed for a ca s t i ron l ap u sed for fini shing are about right A hi gh surface speed cau se s the lap to wear out wi thout cutting as rapidly as i t should M any toolmaker s make the mistake of runn ing laps t oo fast often cau sing unsati sfactory work F or light lapp in g the work can be held by hand but for a heavy roughing cut it i s be s t to hold the work with an ordinary lathe dog care being t aken to see that the dog is not clamped so tightly as to spring the wo k out of shap e L ead lap s should be split to compen s ate for wear and the spindles S hould have a groo ve cu t alon g the i r entire length to p reven t the lap from turning B efore te s ting wi th a s i ze plug the work shou l d be washed wi th benzine or ga s oli ne to remove all traces O f the abra si ve material a few grains of whi ch wi ll wear th e size p lu g b e low s tandard S i ze i n a surpri s ingly s hort t i me M any toolmakers look on the fini s hing of j I g bushi ngs by internal grinding as a rather uncertain method wherea s it is a comparatively simple process when the followi ng important factor s are ca efully con sidered F irst proper selection of grind ing wheels ; s econd correct wheel speed s or at lea s t as n early -

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B U SHI NGS

83

corr e ct as th e d e si gn o f th e machine wi ll pe rmit ; thi rd correct alignment of the h e adstock i n regard to the travel of the p laten ; and fourth pro p er tr ui ng of wheel s Wheels for internal grinding should be of a m e di um gri t soft grad e and o p en bond A s a rule the gri t should never be finer than 6 grit ; i n fact a coar s er grit can often be used to adv antage Wheel s with fine grit cut slowly and fill up readily glazing and i nvari ably heatin g the work an d causing chattering and other troubles In f act th e only argument in favor of a fine gri t wheel i s that i t leaves a smooth surface H owever no matter how smooth the surface appears e ven under a p owerful gla s s i t must be lapped to remove the wheel marks F or the internal grinding of j g bu shing s aloxite whe e ls 1 % — i nch i n diameter i nch face 60 grit P grade D 4 9 5 bond may be used wi th g ood results the wheel speed bei ng R P M F or bu sh i ngs averagi ng 2 % i nche s long % i nch h ole the holes rough-bored inch bei ng left for grinding the grinding time p er bushi ng including chuckin g and truing up would b e about twelve minutes each and the fini sh left good in ch b e ing su fficient to lap out the wheel marks R efere nce i s made to the hole s being rough bored ; thi s is good p racti ce as th e rather rough surfac e tends to wear the wheel just a li ttl e W hi le remo vi ng the fire scale thus p reventing the whe e l from glazing O nce the scale i s removed from the hole the wheel should not glaze r e adi ly p rovi ded i t is of the p rop er gri t and g rade Wheels f or i nt e rnal gr i nd i ng should be run at a surface speed o f 5 000 feet p er m i nut e Thi s h ow ever is a general rule O p en t o excep tions A safe p racti ca l ru l e to follow i s to sp eed up the wheel i f i t wears away too readi ly and to reduce th e S peed wh e re the wheel shows a t enden cy t o glaze A ttenti on to thi s rule wi ll often s ave much trouble The toolmaker should bear in mi nd the fact that it i s ea si er to adju s t the speed to suit the wheel than it is to try to k e e p on hand a large variety of wheels to su i t all speed co n di ti ons A ssumi ng that the work i n question i s to be done on an ordi n ary u ni versal grin d e r the headstock mu s t be s e t p arall e l wi th ,

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D E SI GN

J IG

th e t ravel o f

the p lat e n to produc e s trai gh t h ol e s A p racti cal way to determine p aralleli sm is to clamp a pi ece of round stock in the headstock chuck l e tting it projec t from the jaw s a littl e farther than the length of the holes to b e grou n d Thi s piece should have a groove turned in it for the wheel to dwell in during reversal This test p iece i s then ground in th e regular way wi th the wheel u s ed for cylindrical work the headstock b eing adjuste d by means of i t s swi vel bas e unti l the t e st pi ece i s ground p arallel B efore cali p er i ng the wheel should be al lowed to grind until very few spark s ar e vi sible Wh en once thi s test piece has been ground straight the setting c an be de pended upon to produce straight holes provi ded of course that the swivel adju s tm e nt of the head s tock and th e ang ular adjus tm ent of the p laten ar e not disturbed To try t o align the headstock by calipering th e work while the i nternal g rin di n g i s in proces s is at best di ffi cult and the o p erat or i s nev e r sure of accurate re s ults It is common p racti ce to true wheels for i nternal grindi n g with a di amond fed by hand u sing the eye as a guide This i s p oor pract i ce as the wheel i s seldom turned p arallel on e edge being left to do all the cutting whi ch glazes it readily A more p ractical way to true these comparativ ely soft wheel s i s to fe e d them p as t the end of a carborundum rub in 2 0 grit H grade The rub can be held in a s uitable holder strapped to the platen of the grinder or held firmly by hand agai nst the end of the work A carborundum rub shows high e fli ci e ncy whe n used for thi s purpose In holdi ng work in the Chuck for internal gri nding i t i s well to exerci se due care to see that the work i s not clamped hard enough to spring it out of shap e A s a rule it does not requir e much pre ss ure to hold work of this nature as the grindi ng cut i s comp arativ ely light A s it i s general practice to grind internal work dry a certain amount of exp ansi on from frictional heat i s always p re s en t F or this reason considerable care has to b e u s ed in cali perin g the work with the sizing plug A s th e p lug i s many degree s cooler than the work it i s liable o n being in serted t o contract the bu shing suddenly causing bushi ng and p lug to .

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B U SHI NGS

85

freeze together firmly This can b e avoi d e d by co oli ng the work with a plug that i s kn own to be u n d e rsi ze befor e calip er in g wi th a plug of the de sired size When a wheel of 60 grit i s u s ed a hole o ne i nch or under in di am e ter should be left app roximately inch undersize Thi s amount is sufficient to lap out the wheel mark s and leave a dead smooth mi rror fini h to the hole T hi is a general rule ba sed on the fact that a certain amount !in thi s case inch) i s enough allowance to lap out the mark s left on a surface by a grinding wheel and that S hould suffi ce for all holes regard le s s of size With comparativ ely large holes one an d one half inch di ameter or over it i s better however to make allowance for finishin g owing t o the fact that the area of contac t of whe e l .

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18.

A

H l di g B u hi g great and the ground surfac e is no t

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and w ork is generally not so quit e so smooth In regard to the external grindi n g of bu shi ngs th ere ar e two i mp ortant points that s hould be giv en con siderati on : the selec ti on of wh ee ls and the method of holding the work The whe e l should be fas t cutting and at the same time it s hou ld hold i t s shape and leave a good fini sh F o r thi s work good results may be O btained wi th an alox i te wheel of 2 inches diameter 3 i nch face 5 i nch hole 4 0 5 grit N grade D 4 9 7 bond the wheel being run at a sp eed of 8 00 R P M When a number of bushi ng s arc to be ground one after ano ther i t is be s t to mount them on arbors of the s ame len gth wh en practicable to do so thus saving considerable time generally sp en t i n re setting th e p laten whi ch has to be done whene ver the tailstock i s moved to accommodate arbors of diff erent l engths A n arbor for holding bu shings should be made as S ho wn in F i g The s traight p art should be a good fit in th e 8 .

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bushi ng a sli gh t t ape r o n t h e remain der o f th e arbor b eing suffi ci ent to pr even t the bushing from turnin g o n th e arbor Wh e n bu s hings are hel d on an ordi nary arbor or man drel the O perator is never qui te sure that the hole and the ou t s i d e O f the bushin g are concentric as one end of the arbor owi ng to i t s taper does not quite fill the hole Thi s i s i llustrated in F ig 9 8 and 9 are somewha t exaggerated t o i llustrate B oth F igs the p rinciple In grindi ng lini ng an d solid bushi ngs due allowanc e must be mad e for a driving fit i n th e body of the jig Th e r e are three methods in common use for making driving fits o n thi s Class of work : F irs t gri nding the bu shi ng unti l the lower end just en ters the hole the bu shing being slightly tapered to bri ng i t t o a s nu g fi t wh en p r e ss e d into p lac e ; s e cond g rin ding th e ,

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Or

Ab

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bushi n g straight for i t s entire length leav ing i t jus t en ough overs ize to make a good d iving fit ; and third grin di ng the bu shing for nearly its entire length ju s t enough oversize to make a good driving fit and grinding about one eighth its l ength ju s t enough un der size to enter the hole Th e firs t method i s not con sidered very good p racti c e as the bushing contract s more at the top t h anelsewhere owing to the taper which leav es the hole i n the bu shing tapered Th e se c ond m e t hod i s v e ry p oor practice as the bu shi n g is li able to cramp whi le b eing forced in place whi ch re sults in an unsat is factory job as the hole i n the jig i s generally s heared b y the The third method i s correct as the S harp e nd o f t he bushi n g p ar t tha t is g roun d to fit the hole act s as a pilot thus in suring the p rop er starting of th e bu shin g and th e body being s traight i nsures even contracti on I n making allowances for drivi ng fits in ch f or e ac h ,

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87

i nch

diam e ter of the bushing is con sidered practical wh e re th e holes are on e inch or over a n d where the holes in the jig ar e bore d smooth If the holes are rough bored a more lib e ral allowance i s requir e d A fter the lining bushings are dr i ve n In place they requi re re lapping as they always contract a little The outs ide of the removable bu shing s should be finished by lapping to a dead smooth finish as otherwise they will soon wear loos e Thi s should never under any Circumstan c e s be done wi th em e ry cloth but with a cast iron lap as illustrated in F ig 2 0 Th e abras iv e used in thi s ca s e should b e of flour gri t wi th lard o il as a lubri cant the abrasive and oil b eing appl ie d through a hole in th e t op of the lap The w ork should be lapp ed wi th a reg ul ar e ve n mo ti o n to in sur e i ts b eing ,

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F i g 20 Lap for F ini s hi ng O t s d e .

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S i

straight and s hould b e b ou gh t to the temperature of the room by b ein g cooled in benzine or gasol ine b e for e t e sting for a fit Th e lapping should be carri ed to a p oint where the bushing is a wrin gin g fit in its lin er but n ot tight enough to st i ck wh en l eft for a mome n t A fter the grin di ng and lappin g of the remo vable bushi n gs the i r tops can b e fini shed by lapping on a carborundum ston e in med i um grit wet with gasoline A regular motio n should be used across the face of the stone without turning or altering the r elat iv e p osi tio n of the bushing This lapping gives th e bushin gs a good appe aran ce and as the dimension s stampe d are left black from the actio n of th e fire in hardenin g they can be r e ad a t a gla n ce S tandard d ime n Dr iving F it All owanc e s for J ig B u s h ings sions for driving fit allowance s for j ig bushings arranged ac cordi ng to th e outside diameter of the bushing are give n in ,

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Table VI O ftentime s d ifli cult y i s experienced in a s sembl ing the bu shings on account of n ot havi ng allowed the proper amount of s tock for fitting P lat e B ushing H ol d e r s for Multi pl e D rilli ng Wh e n a number of holes are to be drilled and reamed on a multiple spindle machine the mo s t S imple method i s to place the piece in a suitable j ig and use individual S lip bushing s s o that after the hole s are drilled the bushi ngs can be replaced with reamer .

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All

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w anc e s for

D

ri vi ng

D ill B u

F i t for

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s h in

gs

size bu shings the j g mo ved und e r the reamers and the hol e s achi ned The lo ss of time in ha ndling the s e slip bushings i s so great that the p roduction costs increase v ery rapidly e sp e cially wh e n the op erator has to stop to p ry up bushi ngs with a screwdri ver or s ome other t ool as is ofte n th e ca s e Thi s style of bushi n g will freque n tly catch the drilling or r e am ing tool and turn with i t thu s weari ng the bushi ng plat e To preve nt i ts turni ng the groove cu t bushing is sometimes u sed This consists of an ordin ary slip bushing in which a slot is cut spirally aroun d on e quarter of the outer periphery Thi s slot engage s a pi n i n the bu shing plate so that when th e bushing starts to slip the pin preve nts i t s maki ng a full turn A mo di ficat i on of thi s method was described in connection wi th F ig 2 One s ource of trouble from indi vidual s lip bushings i s the accumulati on of chip s Which mu s t be carefully remo ve d befor e the bu shin g s are changed ; another i s the pos sibility of int e r

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0 9

or two slots The r emo vable bushing p lates us e d wi th thi s frame have holes or hinged b in ders to corr e spond with these pin s or slots and so are correctly locat e d G ui d e B u s h ing s att ac he d t o Drill s Wh e n se veral small hole s nece ssitat ing two or more operations are to be mach ined the following plan work s we ll from a production s tandpoint Gu i de bu shings of the same diameter are fastened to the dri lls reamers and other tool s to locate them in the bu shings in the plate whi ch are uniform in diameter Thus when drilling or reaming the tools will be guided from the bushing A F ig This method i s n ot recommended for holes o v er one inch deep a s there is a tendency for the dri ll s to sp ring out of alignment especi ally i f the drilling is done against a rough s urface since the end of the dri lling tool wi ll be some di s tance from the aux Thi s arrangement is e ff ective for iliary bu shi ng gui di ng i t drill in g s teel as the space between the jig plate and the work allows room for the curled chips The di ameter of the guid e bu shi ng however mu s t be kept as small as po ssible sinc e thi s pi ece has a tendency to heat and stick owing to t h e peripheral speed Thi s sticking and the wear o n the bu s hing plate may be a vo i ded by u sing a stationary p ilot S imilar to that shown in F ig 2 2 A Z shaped ca s t ing wi th a bore equal to the tool size and a nose equal to the jig bu shi ng di ameter is secured to the arm of the multiple sp indle drilling machi ne by a bolt that ext ends through the slot in th e arm as S hown in the illustration G e n e r al N o t e s on B ushings When accurate work is ne ce s sary the bushings S hould s upport the cutting tool to within i one d iameter of the too l from the work If a inch drill is used th e end of the bu sh ing s hould not be more tha n in ch from the work and it may be carried to within in ch of the work B u shings should not be loca ted clo s e to the work with the object of carryin g the chip s u p through the bushing It is much better to p rovide other means in the jig for the removal of th e chips The s hape O f th e work frequ e ntly requires bu shings of con s id e r able length in order to carry the cuttin g tool close to the work W hen the length exceeds four diam e ters of th e tool to be guided the bushing presents con siderable friction surface .

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B U S H I NGS

1 9

l ength equal to two diameters of th e cutt in g tool is usually suffi cient for a bearin g surface in the bushing The r e mainder of the length of the hole in t h e bu shing may be coun t e rbored or reliev ed Th e end that should be re lieved is of cours e tha t which is farthest from th e work in to whi ch the t oo l is to be guided S crew bu s h ings are generally avo i ded whe n accurate work i s required Ther e must be a certain amo un t of clearance in the ordina ry tapped hole and a threaded bu shin g i s likely to be out of true on that accoun t S ometime s however it happ en s that no other typ e of bu shing can be u s ed for the work in ha nd The headed or flanged bushing is preferred by many too l designers as a lining bushin g W heneve r i t i s p ossibl e to ut il ize it If it is de s ired to have the h e ad of the bu shi ng flush w i th the surface of the jig the jig is counterbored to receive the h e ad A s pre viously me n tioned slip bu s hings ar e employed wh en s e v eral o p erations ar e to be p erformed through the same l inin g bu shing F or examp l e when it is desired to drill and ream a hole and to finish a boss or sp ot around the hole while th e work is still in the jig a lining bushing is selected that will guide a count e rbore T E inch larger than the boss to be fini shed A slip bushing is then made to guide the drill the body of which is a slidin g fit in the lin ing bushin g An other slip bu s hing i s mad e for the r e amer which is al s o a s liding fit in the lining bushi n g The slip bu shing walls may have an y thickness p roviding they are n ot too thin S hould the conditions require bushings wi th too th in walls the counterboring operation in the j i g must b e abando n ed an d som e different method of procedur e adopt ed A

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C H A P TE R V

LO CATIN G P O I NT S

AD JUS TAB LE S TOP S

AN D

The locating points in a j i g u sually con si s t of fini sh e d pads bo s se s seat s or lug s ca s t solid with the jig as illustrated i n In thi s engraving the surface s marked f are the locat F ig ing p oint s which bring the piece to be machined in Correct e latio n to the bushings guiding t h e drill s or to the gages to which other cutting tool s may be se t Thi s method of locating the work is satisfactory when the work done is finished i n a uniform way and wh e r e there is very little variation in the p arts inserted in the jig P i n s and S t u d s u s e d as Loc ati n g M e an s A n other c om monly u s ed method for locating the work in jigs is by mean s of dowel pin s as shown at A and B in F ig The S ides of the dowel pins which re s t against the work are u sually flattened as indicated so as to give more bearing than a me re lin e con tact with the pins could give and at the same time pr event too rapid wear on the locating pin s as would be the ca s e if the work bear again s t the p in s along a line only S ometime s pins or stud s are in s erted in jigs to act as locating p oints instead of havin g lug s cast directly on the jig as shown in F i g A case where a pin i s used for t hi s purpo s e i s shown in F ig 3 where B i s the body of the jig A the pin in s erted t o act as a locating and resting p oint and C the work located again s t this point L ocating p ins of thi s character S hould always be provided with a shoulder or collar so that they wi ll firmly re sist the pressure of th e work they support without possibility of moving in the hole in whi ch they are in erted n f A common method of i n M e a s o V bl ocks Locat g b y locating cylindrical pieces or surfaces is that of placing the cylindrical surface in a V -block as shown in F ig 4 Thi s V block as a rule is stationary and is held in p lace by screws ,

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D E SI GN

JIG

94

in

mak ing thes e b l ocks of cast iron as mos t of th e sur f ac e s have to be machined and the difference in the cost of material on such a comparativ ely small piece i s v ery slight W hen it i s e s sential tha t a C up and C one L o catin g P o int s cylindrical p art of the work be located centrally either with the outsid e of a cylindrical surface or wi th the cent e r of a hol e ,

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L c ti g P p p assing through the work good locating means ar e p rovi d e d by the de sign s shown in F igs 6 and 7 In F ig 6 the stud A i s countersunk conically to recei v e the work The stud A i s made of machi ne or tool steel and may in many cases serve as a bu shing for guiding the tool In F ig 7 the s tud is turned coni cally in order to enter into a hole in the work Th e s e two Fig

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Fi g

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7

C ic

l S t ud u s e d o c a t i n g W or k i n R e on

a

L c ti R f L t l ti C t f t th J i wi t h R l ti C t Hl locating appliances are always made s tationary and ar e on ly used for locating the work never for binding or Clamping S c r e w B u s hi ng s an d S li d in g B u s h ing s u s e d a s Loc ati ng S crew bushi ngs may be used for locating and clamp M e ans i ng purposes by making t h e m long en ough to project through t he walls of the ji g and by turning a co nical p o int on them as .

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for in a th e

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LO C AT I NG

PO I NT S

95

shown in F ig 8 or by count e rsi nkin g them as shown in F ig 9 In all ca s e s wh e r e long guide bu hi ngs ar e u sed the hole in the bu shing ought to be counterbored or recessed for a certain d i s tance of its length A nother type of bushing whi ch serve s the same purpose as a screw bu shing is illu s trated in F ig 0 Thi s bu shing together with the forked lever D and d amp ing bolt and wing nut s hown will s erve not only to locate but al s o to Clamp the work in p lace This sliding bu s hing g ives very good re sult s and i s p referable t o th e scr e w bu shi n g in cases where accurate work i s requi red ; but as a rule where extrem e accuracy would be required thi s kind of locating means i s not used In F ig the slidin g bu shing A has a close sl i di ng fi t i n the l inin g bu shin g B In the head of the bushing A there are two .

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c w Bu hin g re

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screws with hardened heads which fit i nto elongated slots i n the forked lever or yoke D which in turn swiv els around pi n The eye bolt F fit s into a slot G in the yoke and the win g E n u t t igh te ns down the bu shi ng a g ai nst the work as c l early i ndi cat e d in the engraving A comparativ ely long b e aring for the bu shi n g i s required in order to produce good re sults On work tha t vari es consi derably in size this arrangement works s ome what quicker than does a screw bushing but it i s clearly e viden t that i t is a rather expensive ap pli ance and that th e constructi on o f th e j ig does n o t always p ermi t of i ts app lication In som e i nstanc e s i t is nece s sary to have the scr ew bushi n g movab le sideways for i n s tance when the p iece of work to be made i s located by some finished urface s and a cylindrica l p art is to be provided with a hole drilled exactly in the center ,

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of a lu g o r p rojecti on th e relation of this hol e to th e finished surfaces used for l ocating b eing imma t eri al The p i ece of work being a cas ting would naturally be liable to v ariation s between the fini shed surface s and the center of the lu g particularly if there are other surface s and lug s to whi ch the already fini shed s urfaces must correspond and in s uch a ca s e the fixed bu sh ing for drillin g a hole that ought to come in the center of the lug mi ght not always su i t the ca s ting In such a case so called floating bushings as shown in F ig are u s ed The screw ,

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L c ti g d C l mpi g W k bu shi n g A i s conically rece s s ed and locate s from the projecti o n on the casting It is fitted into another cyli ndrical piece B provi ded wi th a flange on one side The p iece B ag ain set s into the hole C i n the jig body D this hole being large enou gh to permi t the nece s sary adju tment of the jig bushi n g When the bu shi ng h as been lo c at e d c once nt ic wi th the lu g E on the work the nut F ha ving a wa sher G under it i s tightened The flange on piece B and the washer G mu s t be large enough t o co ver the hole C e v en if B i s b ought o ver again s t the sid e Fig

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i di

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B u hing s

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D E SI GN

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p o ints o f thi s

ki nd ar e often mi s taken for bindi ng or clamping devices and the set screws are tightened up an d loo s en e d to hold and release the work when the intention i s tha t these screws should be fix ed when once adju s ted It is not even po ssible to depend upon the Check nut s topping the operator from u sing the screw as a binding s crew A headle s s scr ew therefore is p referable as i t is le ss apt to be tampered wi th The sliding point as illu s trated in F ig s 3 and 4 i s another adju s table locating point which is u ed to a great extent in j ig work A flat piece of work or a plate whi ch i s not perfectly level will always rock if put down on four s tationary locating -

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L c ti g W k points but the di fficulty thu s enco untered i s v ery easi ly ov er come by making one of the locating p oints adjustable and as a rule the S liding point i s u s ed for th i s purpo s e One de s ign is shown i n F ig 3 where A represents the work to be located B t h e sliding point i tself and C the set screw bindi ng i t i n place when adjusted The sliding p oint B fit s a hole i n the j g wall and i s p rovided with a milled flat s lightly tap ered as shown to p revent its s li di ng back under the p re ssure of the work or the tool operating upon the work Thi s de sign of slidi ng p oint i s frequently us e d but it i s not as e fficient as the one i llustrated in F ig 4 In thi de sign the s lidin g point A con i s ts of a sp lit cylindri cal piece with a hole drilled through it as illustrated in the engrav ing and a we dge or shoe B tap e red on the end to fit the sides of the groov e or s plit i n the sliding point itself This wedge B is forced in by a set screw C for the F ig

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LO CATI NG

POI NTS

99

p urp os e o f b in ding th e

slidi ng p o in t in p lac e E vi d e ntly wh en the screw and wedge are forced in the sli di n g p oint is exp anded and the friction again s t the jig wall D i s s o great that it can wi thstand a very heavy pressure without moving P in E p re v e n ts the sli ding point from s lipping through the hole and into the jig when loo s ened and also makes it mor e convenient to get hold of In the accompan ying table are given the d ime n sions most commonly used for sliding p o ints and bindin g shoes and wedges A dju s table s tops are S pe c i al Typ e s of A d j u s t ab l e S t ops us e d to a greater extent i n milling fixtures than in drill ji g s bu t .

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o int s

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S h oe s

B i nd

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the prin cip l e s emp loyed are the same Th e examp les shown i n connection with the following de s cripti on of adjustable stops hav e bee n applied to milling fixture s and i n some cases to drill jigs In F ig 5 is shown the simplest type of adjustable s top provi ded with a helical spring beneath the plunger to p ress i t agai nst th e work The O bjection to thi s type of stop is tha t the plunger A will slip back under the pres sure of the clamps or cuttin g tools up o n the work There is al s o danger of the milled flat on -the plunger clogging wi th dirt so that th e stop will not work prop erly C onsiderable time i s therefore lo s t in u sin g j igs or fix ture s wi th this typ e of stop The method of clamping th e plunger i s al s o slow as i t i s nec e ssary to use a wrench in tightening or loosening the set screw B In F ig 6 i s shown an adjustable s top which is an improv emen t over that shown i n The flat on the side of plunger A is milled at a sligh t F ig 5 .

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D E SI GN

angl e ins t ead of p arall e l with the c e n t er line as in F ig 1 5 Thi s prev ents the plunger from slippi ng after being clamped A piece of harden e d drill rod B which i s kept from turning by a small pin C engaging a flat milled in piece B is u s ed between the p lunger A and t h e clamp A wi ng nut D i s fa s tened to the -

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end of the screw as s hown in order to elimina t e the u s e of a W rench I n F ig 1 7 is S hown another adju s table stop which presents a further impro vement ov er that s hown i n F i g 6 A bronz e bu shing B is driven i nto the base of the j ig and allowed to pro ,

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A s abo e the base indicated lunger is a liding fit i n P v as j the bu shing A cap C i driv en onto the end of the plunger an d extends down o v er the out side of the bu shi ng as indicated making the s top dirt proof Thi s s top however as well s that shown in F ig 6 i not entirely sati sfactory b e cause it will e ct

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102

D E SI GN

J IG

In order to overcome thi s diffi culty an adjustable stop as h as been de signed shown inF ig The fla t style of wedge i s abandoned and the wedge A i s made of drill rod and slides in a hole drilled in the ba s e of the fixture The stud at the back e nd of the wedge is s crewed into it instead of being riv eted a in the p reviou s example B ushi n g C is p rovi ded wi th a shoulder and a headle ss s e t s crew D is added to p rev ent plunger E from dropping out when the fixture i s not in use The wedge A i s subjected to consi derable fri cti on and the fixture i s therefore n ot S O sen sitiv e to the touch of the operator a would be de ir ,

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able It is di fficult for th e op erator to feel when the stop i s against the work when tighteni ng t h e wedge in po sition F ig s how s a modi fication of the de sign s ho wn in F i g 2 0 the only Change made being in bu shi ng A which has been lengthened so that it will act as a support for the end of wedge B The bu shing i s made of cold rolled steel and ca s ehardened The bottom part of the ba s e i s cut away in order to reduce the friction between the base and the wedge Thi s design i s better than that shown i n F ig 2 0 In F ig 2 2 i s s hown a somewhat compli cated and expensiv e adjustable s top whi ch howev er h as the adv antage s of almo s t p erfect operating condition s B u shi ng A i s lengthen e d and h as .

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L O CATI NG

P O I NT S

1 03

a much larger shoulder in order to take the thrust t o whi ch it will be s ub j ected when the device i s operated A small pin B replaces the headles s set screw used in the de signs in F igs 2 0 and The arrangements for clamping the wedge hav e bee n con iderably changed and bronz e casting C is added A hole i s cut in the ba e into which the ca s ting i s ins e rted clearance .

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W e dg e

19

being permi tted all around s o tha t the casting can be a li gn e d easily with the wedge The casting is held in place by two filli s t e r head s crews and two dowel s ; a hole i s drilled through the lower p art of it which act s as a s upport for the back end of the wedge as indicated The front end is supported in the bushi ng A i n such a manner that the friction i s reduced to a .

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F ig

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f ct y F m f Adj u h w n in F i g th n th t

S at i s a

a

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W e d ge

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mini mum C asting C al s o supports the shoe D and rai ses it from the ba s e of the fixture A ton gue i s cut on the lower side of s hoe D which fit s into a groov e i n casting C thereby prevent ing the shoe from turning when the nut i s tightened or loosened S tud E is screwed into the side of the knurled nut and a small pin F is dri ven into the s hoe Thi s pin act s as a stop for th e .

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J IG

I 04

D E SI GN

tud prev enting the operator from turning the nut more than i s necessary in tightening or loo s en i ng The adjustable s top shown in F ig meets practically all requirements p laced on an adjustable s top It will not S lip back under the pre s sure of the s top ; it will not slip in tighten ing ; it is dirt proof ; all the parts form integral part s of the j ig ; and it will not become loo s e due to v ibration of the machine or spring down under the pressure of the cut due to unevenne s s of the table s of the machine s on which the fixture i s u s ed It c an be rapidly operated and i s so s en iti v e that the operator fe els instantly when plunger G i s in contact with the work s

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The only objecti on to this de sign is that s o much of the metal of the base has been cut away that it is s eri ou s ly weakened and the desi gn shown in F ig 3 i s sup eri or i n thi s respect In the mak ing o f the fixture difficulti es were also encountered in alignin g the hole s in bu shi ng A wi th the hol es in ca s ting C This was remedied by making the bushi ng an easy F ig 2 fit and addi ng a small pin D and the round head s rew C F ig to keep the bushi ng from turning or working loose The 23 wedge was also jointed and made in two parts as indicated in order to take care of the v ari ation s that migh t occur i n drilli ng

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D E SI GN

JIG

of expansion s o that when the s tud B which i s turn e d to fit the tapered hol e i n the bushi ng is screwed down the bu shi ng i s exp anded Locat ing b y K e yway s i n t h e W or k S ometi mes the work t o be finished in the jig i provided wi th a keyway or a slot or with s ome other kind of a s eat by mean s of which it is located on its component part on the machi ne for whi ch i t i s ultimately in ,

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tended and it is alway s e ss ential that the work be located i n the s ame way in the jig as it i s to be located on the machine on which it i s to go ; thu s if the work has a keyway suitable for locating a corre spondi ng keyway ought to be put into the ji g and the work located by mean s of a key as s hown in F igs ,

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M ill d e

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In i

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and 2 6 Instead of a loo s e key a tongue may be p laned or mi lled so li d wi th the ji g but as a rule i t is more satisfactory t o have the loose key as if it should happ e n to wear i t i s pos sible to replace i t ; and if the wi dth of the keyway S hould v ary i n diff erent lots of the p arts made it is po ssible with little ex p ens e to make a new k e y to fi t the variation whereas if th e key is made solid with the jig and found to be e i ther too large or too small the trouble of fixing this would be considerably greater 25

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LO C ATI NG

PO I NT S

I O

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mmon De fe ct s i n J ig D e s ign The fir t co n sideratio n o f the jig designer should be to determi ne what degree of accuracy is essential in the part that i to be produced and al o whether absolute interchangeability i nece sary Thi information will be a guide for the economical production of the jig The de signer mu t also con ider any operation whi ch are to be per forme d on the work prior to the one for whi ch the jig under con iderati on i intended ; for whi le thi preli minary machining may not need to be accurately done inaccuracy or uniformity may re ult in improperly locating the work in the next jig Co

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h w o

H l di o

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P

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should be so desi gned as to l ocate the p ar t wi th the re qui red accuracy Th e locatin g p o ints of an y j i g should b e such as to allow as wi de a range of inaccuracy on any preceding operation as i s compatible in the part F or example if the part h as to be turn e d to say a li mi t of inch it will require more skill and time than i f a li mit of i nch i s allowable A gai n as far the p ortion of the work that requires to be the as pract i cable most accurate should be used in locating it in the j i g for the succ ee di ng Operation O ften a surface i s s elected to locate from which in cons equence mu s t be machi ned to an accurate Thi s of li mi t wh e n accuracy otherwi e would be unnece s sary .

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D E SI GN

course only adds to the co s t of produc ti on A f te r co n si deri ng the p oints mentioned the best method of arranging th e detail s of the j i g so that i t h as as few dimensi on s as p ossible requiring absolute accuracy s hould al s o receive attention ; that i s the ji g should be as simple as p o ssible and still be so desi gned as to accurately locate the p art s to be machined In F igs 8 and 9 are shown two jig de s igns whi ch wi ll serve to illu s trate the s e point s The part for which a j ig is required i s hown in F i g 2 7 In the preliminary machining operation the work is turned to diameters A and B and to lengths C and D The limit of accuracy required on end A is or any 1 diameter from % % inch as a minimum to % inch F o r end B a .

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whi ch wi ll h l d n wh n D i m t o

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i s necessary s o that thi s end s hould be u s ed finer li mit of as the locati ng p art for the next operation ; vi a the milling out of the S lot E which must be central wi th the p art B A de sign such as s hown in F i g 2 8 i s not uncommon for thi s op erati on and with it fairly accurate re sult will be s ecured ; but if the loca t ing diameter on the work i s slightly small say inch then the forcing of the piece over to one side by the locking s crew A will re s ult in an inaccuracy in the milling operat i on The locating hole s B mu s t be the exact size of the locating part of the work and unle s e very piece is a pu sh fit !which i s u n ,

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C H AP T E R VI

J IG

M P IN G

CLA

D EVICE S

The clamping d evi ces used in connectio n with j i gs and fix tures may either Clamp the work to the jig or the jig to t he work but very frequently the clamps simply hold in place a loose or movab l e p ar t i n the jig which can be swun g out of th e way to facilitate removing the work from and inserti ng i t in the jig The work itself is in turn clamped by a se t screw or other mean s pa ssing through the loo s e part commonly called the leaf T Type s of Clam s he s i m p lest form of clamp i ng dev i ce is p the so called clamp of whi ch a number of di fferent form s are commonly us e d P erhap s the mo s t co mmon of all clamp s is the one S hown i n F ig Thi s kind of d amp is al so commonly termed a s trap It is simp le cheap to make and for mo t purpose s i t gives satisfactory s e rvice The clamp shown in F i g 2 is made on practically the s ame principle as the one shown in F ig but several improv ement s hav e been intro The clamp is reces s ed at the bottom for a di s tance b d u ce d to a dep th equal to a so as to giv e a bearing only on the two extreme end s of the clamp E ven i f the strap should bend somewhat on account of the p re ssure of the s crew it would be certain to bear at the ends and exert the required pre ssure on the objec t being clamp ed This strap i s also p rovi ded with a ridge at D located centrally wi th the hol e for the s crew This insures an even bearin g of the screw head on the clamp ev en if th e two beari ng p o in t s a t each e nd of the clamp s hould v ary in hei ght as illustrated in F i g 3 The clamp in F ig would not bind very s ecurely un der such circum s tance s and the col lar of the s crew would be liable to break off as the whole s train when tightening the s crew would be put on one side A further imp rov ement in the construction of thi s clamp may be had b y roun di ng the under si de of the clamping points ,

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LAM P ING D EV I C E S

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hown in F ig 4 When a clamp with such roun ded Clamp ing p oint i s placed in a po sition like that indi cated in F ig 3 i t will bind the object to be held fully as firmly as i f the two clamping surfaces were in the s ame plane The hole in the s e straps is very often elongated as indicated by the dotted line s i n F ig and T hi s allows the strap to

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be pulled back far enough so as to Clear the work makin g it eas ier to in ert and remov e the p iece to be held in the ji g In some cas e s it is neces s ary to extend the elongated hole as shown i n F ig 5 s o that i t becomes a S lot going Clear through to th e end of the Clamp instead of being simply an O blon g hole A si de f rom thi s di fference t he clamp i n F ig 5 work s on exactly the same principle as the clamps prev i ou sly shown ,

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The clamp s described may be given a number of differen t shapes to suit different condition s Instead of having the strap or clamp bear o n only two p oints it is sometimes nece ss ary to have it bear on three points in which cas e it may be designed similar t o the strap shown in F ig 6 In order to get an equal pressure on all the three points a special screw with a half spherical head like the one shown may be u s ed to adv antage The half sph e ri cal head of this scr ew fits into a concave rece s s o f .

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J IG

I I 2

D E SI GN

the same S hap e in the strap When th e bearing for the s crew head i s made i n thi s mann e r th e hole through the clampmu s t have plenty of clearance for the body p art of t h e bolt When de signing clamp s or s traps of the typ e s shown o ne of t he most i mportant con siderations i s to p rovide enough metal around the hole s so that the strap will stand the pre ssure of the s crew without breaking at the weake s t place which naturally i s in a lin e throu gh the center of the hole A s a rule the s e st ap s are made of machi ne s teel although large clamps may sometimes be made from ca s t iron .

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gs 7 and 8 S how Clamps bent to meet the requirements and also i n di cate the appli cati on of thi s type of clamp the p art s hown in cro s s section being the work The s e clamps are commonly used for clamp ing work i n the p laner and milling machi ne but are als o frequently used i n jig and fixture de sign The screws used for clamping these strap s are either s tandard hexagonal screws or standard collar head s crews W hen it i s n ot n ecessary to tighten the screws v ery firmly thumb s crews ar e fre qu en tly used espe cially o n small jigs S ome time s th e s t rap or clamp is arranged as shown in F i g 9 t h e screw pa s sing through it at t he center and bearing upon the work eith e r di rectly as indi cated or through the medium of a collar fitted to the end of the clamping screw as shown in Fi

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D E SI GN

JI G

4

which

are v ery much alik e but tha t of F ig 1 4 i s simp ler and more rapidly operated when the work i s t o b e remov e d When the Clamp i s slotted as s hown in th e p lan Vi ew of F i g 1 4 fixed studs may be u s ed instead of the swinging bolts .

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yp

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of

Cl a

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S tra

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The type shown in F ig 5 is often found in machi ne shops o n milling fix tures dri ll j i gs lathe fixture s etc The clamp and bolts can be removed by loo s ening the n ut s and pulli ng out the sli p washers whi ch allow the nuts to pass through the large 1

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C l mp Ad pt d t B Ji g holes F ig 6 i llustrates a method whi ch i s commonly used on mi lli n g fixtures when li gh t mi lling is to b e don e The design of clamp shown in F ig 7 i s not frequently seen in use as it i s a method whi ch a mech ani c wi ll not u s e if he can se e another way out of i t ; bu t at times it i s found almo s t imp o s sible to us e a clamp of a different type F ig

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LA M P I NG

D E VI C E S

1 1

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styl e of clamp that is som ewhat similar to the one illustrat e d i n F i g 2 i s shown in F i g 8 In thi s ca s e howev er two clamp ing bolts are u sed and the clamp i s removed from the end of the ji g Thi s is a good as well as a quick method of clamp i ng work i n op en end drill jig s F i g 9 illustrate s the u se of bolts only for holdi ng down work The i llu s tration is s elf A

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C l mp wit h S wi gi g B lt explanatory F ig 2 0 shows a good de sign of clamp for holdi ng work in a milling fixture It bind s the work both horizontally and v ertically and i s the v ery best type for its purpo s e wh en it can be used F ig

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C l mp H ook-b olt s The hook bolt shown in F ig 2 i s better adap ted for some classes of work than any other clamp in g de vi ce A t the sam e tim e i t i s very cheap t o make and e asi ly applied Th e bolt A p asses through a hole in the j ig having a good S li di ng fit in thi s hole and is pu shed up until the hook or F ig

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D E SI GN

JIG

Dim

e ns i ons

of

Co

ll ar-h e ad

k —D

D im

e n s i ons

of

Sh ul d o

Sc

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ws

use d

on

Jig s

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er

Th

umb -s c r e w s u s e d

on

Jig s C

D im

e n s i ons

of W in g

or

Th

umb -nu t s

for

Ji g s

I 1

8

JIG

D E SI GN

suited to i t s purpose becau s e the bearing point on the work is clo s er to the bolt body S c r e w Tigh t e ni ng D e vi c e s In a box j g or a j g where the work is entirely or almo s t entirely surrounded by the jig the work i s ea ily held in place by set screws which are us e d when ,

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C l mpi a

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i mpl C l m pin g M t h d

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C l mp t h t h l d th W k F i ml y i pl c ever great clamp ing p ressure is required the square head allow in g the use of the wrench S ometimes s crew s of thi s kind may be tightened enough for the purpose by hand if a pin i s put through the head of the s crew as s hown in F igs and 3 This mean s i s u sed not only when great pres sure is not necessary but also when the work i s liable to spring if the screws ar e F ig

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D EV I C E S

CLAM P I N G

I I

O

tightene d to o hard I n such a cas e if a pin is in s e r te d it i s obvi ous that th e scr ew head i s n ot inten d e d fo r a wr ench bu t that th e pin i s in t en d e d for g et tin g a g o o d grip by the h an d for t ight enin g the screw wi thou t r e sor ting t o any addition al mean s U sually i t i s n o t p ossib l e t o us e an o rdinary machi ne wr en ch o n such a screw Wing-nuts ar e gene rally mos t sa t i sfac tory fo r j ig s whe r e only a ligh t b in ding p r e ssur e i s r e qui r e d Wing nuts are us e d o n h ook -b o l t s or swiveling eye-bo l t s wh en a comp arativ ely ligh t p ressur e i s requir e d Th e thumb .

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H ok-b ol t M e th od o

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o r wing-nut i s p r e f e rab l e to a knur l e d n u t as it giv e s a b ett er grip a n d mak e s it p oss i b l e t o tigh ten the b o l t m o re fi rmly Th e di men si on s o f a n exc e l len t d e sign of h an dwh ee l for use on j ig s , e t c ar e given in a n accomp a nying tabl e Thes e whee ls h ave a ra ther l ong st em o r hub whi ch p rovi d e s a g ood l en gth o f th r e ad and brin gs th e grip or h an dl e f ar en o ugh f romth e jig body t o p r event “ t h e fin g e rs o r knuck l e s f ro m s t rik in g i t The star d e si gn o f han dl e also p e rmi t s a good grip B y having th e casting sol id th e s e handwheel s can be tapp e d out for any siz e thread or a ,

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1 20

D E S I GN l

plai n

hol e can be d rilled when i t is desired to at t ach t h e han dl e s t o round s tock If screws are t o b e fi rmly ti ghte ned wi thou t t he us e o f a wrench the me t hod o f using a pin throu gh the screw h e ad shoul d b e use d o nly on l arge fix tur e s wher e the pin i s 5 i nch .

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B i di g S c w in di ame t er and requi r e s th e use of both hands an app li cati o n of whi ch is shown i n F ig 2 6 On smaller sizes of fix tures wh e r e in ch in ameter by t h e pin is abou t 3 d i 4 inches long a n d must ; be us e d wi th on e hand th e p r e ssure is concentrated across th e F ig

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Pin

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Bi di g S c w p alm of the h an d a n d i f t h e fix t ur e i s us e d f r e qu ently it i s lik e ly to develop a sor e sp o t In t h e case of the hand kn ob shown i n F ig 2 7 however it i s evi d e nt tha t t h e p ressure i s di stributed o ver the p alm of the h an d and therefor e t h e like lihood of producing a sore i s much l e ss Tables of s izes o f two diff eren t typ es of kn obs for differ e n t c l ass e s o f fix t ur e s are g i ven her e wit h F ig

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me nsi ons

Di

D im

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D im n i e

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of

D E SI GN i J g s cre w Latch e s

R e gu

of

l ar

mb -s cre w s

Th u

mb-s cre w s

Th u

w ith Wi d e G rip

Th e qu e s ti on s n aturally arise how much p re ssur e can a man e x e rt wi th hi s finge rs in op erati n g a kn urled-head scr e w how much p res sure can h e d evelop wi th a scr ew and han d knob and how much p re s sure can h e exert in op erating a screw wi th a p in through i t ? It i s qu i te safe t o say that for co n tin uous ope ra ti o n o n jigs or fix tur e s al l that c an b e d epen d e d up o n wi th a knurl ed -h e ad screw i s to b rin g th e scr ew up t o s te ady the work but wi th a scr ew and p in through it i t is not u n commo n ,

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LAM PI NG D EVI CE S

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3

With a hand kno b th e amoun t of p r e ssur e i s doubtful and depen ds largely up o n the p o sition of th e scr ew wh ich gov e rn s th e grip obtainabl e o n th e knob Th e eleme n tary p rinciples invo lve d in S wingi ng Le ave s the swinging leaf Clamp ing construction are s hown in t h e ir sim i 2 F 8 L v form in oose lea es w ch swin g out in order hi t l e s g p to b en d t he pin

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to p ermi t the work to be i ns e r te d an d removed are usual ly constructed in some manner S i milar to tha t sho wn in F ig 2 9 in which A repr e s ent s t h e leaf bei ng p iv o te d a t B an d h e ld b y a p in at C which go e s through th e two lugs on the ji g wall and pas es through the leaf thus binding the leaf and allo wing the ,

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1 24

ti ghtening

D E SI GN

of th e set screw D whi ch bears again s t the work The holes in the lug s of the casting s are lined wi th steel bu sh ing s in order to prevent the ca s t iron holes from b ein g worn out too soon by the constant p ulling out and p uttin g in of the p in Thi s ki nd of leaf when fitted in nicely i s rather expensive but is used not only for binding purpose s but also for gui di n g purp oses makin g a conveni ent seat for the bu shings If leaves are fitted well in place the bushi ng s i n the leaves will gu i d e the cutting tools in a sati s factory manner A nother method of Clamping down the leaf i s shown in F i g 3 i n which A is a thumb s crew screwed directly into the wall B of the jig and holding the leaf C down as indi cated To swing the -

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C l mpi g D ill J i g L f lea f out the thumb s crew i s turned back about a quarter of the turn so that the head of the thumb screw s tand s in line with the s lot in the leaf thi s slot being made wide and long enough to permit the leaf to clear the head of the thumb s crew T hi s i s a v e ry rap i d way of clamp ing and is frequently u s ed The lower side of the head of the screw will wear a long time before th e head finally comes i n line with the slot when binding It can then easily be fixed for binding the leaf again when standi ng in a po ition where the head of the thumb -screw i s at right angles to the slot by turni ng off a portion of the head on the under si d e F ig

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3

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E y e -b ol t

u d se

f or

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ea

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D E SI GN

J IG

to b e dri ll e d can b e p ut i n p lac e in t he j i g This r e qu i r e s a l o cking dev i c e whi ch can b e depen ded upon to hold the bushin g p l a te exactly in p lace whil e dri lli ng Th e locking d evic e shown i n F ig 3 3 an d also shown app lied to a j ig in F ig 3 4 answers this purp ose ad mirab ly To op e n the jig so as to put in the pi e c e to b e drilled all that is nece s sary to do i s to push the .

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A J i g L c ki g T i gg butto n on the e n d of t h e lock trigg e r and li ft th e leaf u p When the p ie c e i s i n place in the j i g the l e af is again p resse d down into place Th e pr e ssure springs the locking device and the trigge r grip s the pin shown The p art of th e trigger which F ig

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L c ki g D i c i F i g 3 3 ppli d t J ig fi t s agains t the pin should tape r sligh t ly This mak e s i t hold much more ti ghtly and also takes up what little w e ar th e re may b e o n i t Th e device can be fitted to a great v ariety of ji g s an d fixtures It i s v ery simple and in exp en sive to make i s qui ck an d si mp l e to O p e rat e an d i s p o sitive in its ac ti on A hi n ged jig cover may also be co nv e ni e n tly held i n p lac e by m e ans of a spring latch of the form shown in F ig 3 5 whi ch i s F ig

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A M PING D E VI CE S

12

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s emi automatic in its action In th i s i llustrati on th e b o dy of th e j i g is sho wn at A and the hinged cover a t B Th i s cov e r swings o n th e pivo t C and drop s on to th e latch D which tak e s th e p lac e of th e l ocking scr ew arrangem e n t shown in F i g 3 6 an d whi ch shows an app li ca tion of th e p rin cip l e i llus trat e d in F ig 3 0 I n cas e s wh e r e the c ov e r i s m e r ely us e d t o carry bush ings a la t ch o f thi s kin d i s en ti rely satisfac t ory al though it is n ot r e comm en d e d f or us e on jigs wh e r e screws f or holdin g down the work ar e carri ed by th e cover The me thod of u sin g i s e vi den t f rom the illustratio n To swing th e cove r clear of -

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L t ch th e work in t h e j i g th e latch D i s p ushed back in th e di r e c ti o n o f th e arrow A ft e r the cover has been rai s e d th e l a t ch sp rings back in to p lac e ready t o ca t ch over th e t op of the cove r wh en i t i s droppe d back onto th e j ig When the cover is droppe d th e l a t ch catch e s it au to mati cally requ i rin g n o atten ti o n from th e O p e ra to r A n umber o f app l i cati o n s tha t vary in d e tai ls only ar e shown in F ig s 3 7 t o 4 0 F ig 3 7 S hows th e styl e o f clamp that is used in conn ecti o n wi th b ox dri ll ji g s wh e n it is desired to supp ort a p art to b e dri ll e d on two point s As wi ll b e s e en th e s e two bearing poi nts are s el f-adjus tin g Th e d e sign of F ig 3 8 is g e ne rally u s e d when it is desir e d to supp or t the work in two place s i n F ig 3 5 .

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J i g wi th Cove r h e l d b y S p ring

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D E SI GN

an open en d dri ll j i g F igs 3 9 an d 4 0 show type s which ar e quit e similar but there are many cases where one type can be u sed to advantage and not the other F or in s tance th e Clamp F ig 3 9 is i nt e nd e d for box ji g s b ut the type sho wn in F i g 4 0 could n ot be used f or s uch a j i g because the lat te r i s alto gether too slow H owever its advantag es over F ig 3 9 in ca s e -

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ove r

J i g C ove r

L ck d e

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wi th

by

Qu

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Two-point S e l -a

S

,

c w re

s t ing

Cl a

mp

desired t o hav e an op en e nd j i g ar e apparent The r e lati on of th e firs t cost o f a ji g to th e quan ti ty of work to b e done is a factor whi ch som e ti mes makes a ji g whi ch i s not p erf e c t from a purely mechani cal standp oin t mor e de si rable than one which rep resent s bett e r de si gn but greatly i ncreased co s t The ordinary jack-screw is employed quite commonly as a clamping device in drill jigs but the obj e cti on to i ts us e is that is

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130

t h e r e by p r o vi ding a c l amping d e vi c e whi ch may b e sai d to p oss e ss doubl e adjus tm ent Thi s d e vi c e mak e s a v e ry con It w orks sa tisfac torily an d has v e ni e nt clamping arra nge m ent the advan t ag e of being easi ly swun g ou t o f th e way Th e p rin cip l e o f clampin g work i n th e W e d ge or Tape r G ib i i 2 F by m e a n s of a w e dg e or tap e r gi b is show n i n a n d 4 j g g two applicati on s are illustra t ed in F igs 4 3 and 44 I n F ig 4 3 .

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C l m pi a

D ic

W or kin g P r i nc ipl e

ng

ev

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on

th e

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Jack -s c e w r

Appli c ti f W d g Cl mp the work is l o ca te d b etween th e wedg e A an d the wa l l B o f the j ig and pressed agai ns t the w all by th e wedge which c an be drive n in by a hammer or screwed i n place wh en th e j i g i s con s truc te d as shown I t i s p r efe rab l e t o hav e the we dg e scr e wed in p lac e as it i s the n l e ss lik e ly t o l oos en by th e c on sta nt vibra ti ons to which i t is subj e c te d and at th e sam e tim e the wedge F ig

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Si

mpl e s t

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on o

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LA M P I NG

D E V I CE S

1

3

1

i s l e ss li k e ly to get l o s t b eing a n integ ra l p ar t of t h e j i g T he e ar fo r t h e scr e w may b e p l ac e d in a ny di r e c tion in r e gard t o th e gi b as i n d i ca te d by th e do t t e d lin e s in th e en d v i ew o f T hi s tightening d evice is i n particular adapte d t o F ig 4 3 work of dove t ai l shape as shown in F ig 44 I n this cas e the we dg e i s mad e s i mi lar to th e co mmo n t ape r gi b us e d f or t aking up th e w e ar in dov et ai l s li d e s I t i s som eti m e s o f advantage to r eliev e th e bearin g surface opp osi t e th e w e dg e as shown in ,

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F ig

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W e d ge

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44

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W e d ge

or

p

Ta

for C

er

G ib

l mping a

u d se

D

for

C l m pi a

ove t ail e d

ng

W or k

do tte d line s in F ig 4 3 in ord e r t o p r ovi d e two di s tin c t b e ar ing p oint s whi ch p r eve nt t h e work f rom r o cking T he ho l e in th e e ar o f th e gi b t hrough whi ch the scr ew p ass e s mus t be oblo ng so that when th e scr ew i s adjus te d an d th e gi b move d in or out th e re i s ampl e allowan ce for th e sid ewi s e mov em en t of the e ar du e to t h e tap er o f th e gi b If it i s r e qu i r e d to get a b e arin g on two point s of a surf ac e th at i s lik e ly to va ry in it s d i m en si o n s a yok e can b e us e d de si gne d on th e prin cip l e o f th a t sh own in F ig 4 5 In th e .

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32

J IG

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D E SI GN

engravi n g A i s th e work t o b e clampe d a n d B i s th e yok e whi ch fits into a slot in t h e c e nt e r of the s trap or clamp C Th e yoke i s h e ld by a pin D around which it can swivel to adjust it s elf to the work It is evident that the amount of p re s sure at the t W O p O lnt S E and F will be equal or at leas t near enough so for all practical purposes even though th e scr ews at the end s of the strap may not be equally tightened In thi s device the ,

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F ig

Fi g 4 6 .

pi n

45

.

.

E

.

E

qu ali zi ng Clam p

cc e ntri c Cl m ping a

B lt o

t akes th e full Clamping strain and shou l d there f ore be designed s trong enough and th e strap which is weakened by the slot and the hole i n the center should be reinforced as indi cat e d a t thi s p lace It is preferable to have spi ral springs at each end of th e strap t o prevent the strap from slipping down whe n the work is take n out The strap may be made either of ca s t i ro n or machine steel the yoke being mad e O f machi ne D

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steel

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D ES I GN

J IG

34

in g p urp os e s ne c e ssary guid e s mus t b e p r ov i d e d for the s t rap so as to hold it in the r e quired p osi ti on Th e s e gu i din g arrang e m en ts may consi st of rigid rods grou n d and fi t te d into dr ill e d and reamed holes in the strap or square bar s held firmly in the ji g and fitted into square slots at the end s of the strap The bars may also b e round an d th e slo t s at the e n ds of th e s trap half round the p rincip le in all cases remaini ng the same ; but the more ri gid the gu i di n g arrangem e nt i s th e mor e may the accuracy of the locating be d epended upo n The ordinary eccentric l ever works on the same p rin cip l e as ,

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the eccentric rods just de s cribed There are a great v ariety of eccentric Clamping device s but they ar e not as commonly u s ed .

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C l m pi g i n p resent day j i g d e si gn as th e y wer e a few y e ars a g o The eccentri c clamp ing levers however p rov i de good and rap id clamp ing acti o n I n F ig 4 8 i s shown o n e espe ci ally i nten ded for clamping fini shed work It i s not advi sab l e t o us e this kind of l ever on rough casting s for the reason that the latter may v ary so much tha t the cam or eccentr i c w ou l d r e qu i re too g r e at a throw for rigid clampi ng to suit th e rough castin gs The extr em e throw of th e e cce ntri c lever should in g eneral n ot exc ee d o ne S ixth of th e leng th o f the radius o f th e ecce nt ri c arc if th e ri s e tak e s p lac e during o ne -quart e r of a comp lete turn of the leve r Thi s wo uld gi ve a n extrem e t hro w of say 3 i n ch for a le ver having 3 inch radius of the camor ecc e ntric It i s plain that as the eccentric cam wi vels about the center A F i gs

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48

and

49

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Ca

m

s

or

E

cc

e ntr i

c u d s

se

for

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s

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CLAM PI N G

D EV I C E S

13

the

5

lev e r being conne c te d t o th e j i g with a s tud o r pin th e f ac e B o f th e cam which is struck wi th the radi us R f rom th e ce nte r C rec e des or approach e s the s i d e of the work t her e by rel e asi n g it from or clamping i t again st the bottom or wall of th e j i g T h e l e ver f or the e ccentri c may be placed in a n y di r e c tion as ,

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F ig

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50

A ppli cati on

.

of

C

l am ping

m

Ca

i n di ca te d b y t h e full and dotted lines in F ig 4 8 I n F ig 4 9 i s S h own a not her e cc en tric l ev er which i s us e d f re q u en tly o n small work fo r holdi ng down strap s or leave s or for pulling togeth e r two sli di ng pi e c e s or on e sli di ng and one s tationary part which i n th eir turn hold the work These s li din g p iec e s may b e .

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C l mpi g V blocks or some k i nd o f jaws Th e cam lev e r i s a tt ach e d t o the jig body the l e af or the jaw by a pin through hol e A The hook B en g ag e s th e s tud or pin C wh i ch i s faste ne d in th e opp osite jaw or p art whi ch i s t o b e c l amp ed to the p ar t into w hi ch th e pin through hol e A i s fast ene d Th e var iety of design of e cc ent ri c cam l ev e rs i s So grea t tha t i t i s impo ss i b l e to S how more than the principles but the examp les s hown F ig

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51

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Th e

“

G ri

pping

M e th od

Dog

of

a

n

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9!

13

6

J IG

D E S I GN

embody th e u n derlyi ng actio n of all the diffe r ent d e sign s A n elementary app lication is shown in F ig 5 0 Irregular shaped cas tings which must b e machi ned ofte n p re s e nt no appar e ntly good mean s of holdi ng by ordinary grip ping appliances for drilling shap ing or milling In such ca s es a gripp ing dog as i llustrated in detail in F ig 5 may be used The bas e block C of the dog is slotted to receive jaw D which i s fulcrumed on a cross —pin In the tail of the dog i s threaded a set-screw E and by turning in thi s set-scr ew the jaw is caused to bite inward and downward at the same time firmly .

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F ig

.

Wor k

5 2.

H

e

ld

cl amps

b y V-

p ing

the cas ting and forcing it down on the tabl e A backstop F i s bolted behi n d each do g so that th e re is no cha n c e for slip p ing away from the work The p recedi ng d e s cri pti on an d Appli cati ons t o J ig De s i gn illu s trations i n dicate the p rin ciples embodi ed i n jig clamping devices The followi ng typical illu s tration s s how a number of applica ti ons that are merely modifi cation s of the v arious methods already revi ewed M o s t of the devi ces de s cribed may be quickly opera t ed the purpose being to show a col l ection of effici ent designs that will hold the work s ecurely They posse ss th e further advantage of being relati vely simple so that the jigs can be made at a mod e rat e cost in all cas e s where th er e are .

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D E S I GN

on the end of the adjus tin g scr ew e n t e rs a hole in th e V block the two members being held together by a p in which fits i n a g roove i n the p ilot The movable V block i s held to th e body of th e jig by two s t eel strap s F ig 5 3 i llustrates i n th e upp er View another method of attachi ng a s crew to a s li d i ng clamp m e mb e r In thi s ca s e the sli di n g p iece is used for f orci ng th e work down i nto p lace T hi s screw run s i n a tapp ed hole in a stationary part of the fixture whi le the collar at the end of the screw fits into the movable wedge to pu sh it forward or draw it back The lower View hows a mov able c l amp A

p ilot

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s

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ECCEN RIC IN T

B

DER

R

WO K

F ig

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55

.

Hi nge d

Cove r

wi th

Fl oat i ng S tu

d

member that has a tapp ed hole to receiv e the adju s ting s crew H ere two collars on t h e screw are located at each side of a boss on the fixture and t h e adjustment i s Obtai n e d b y the screw turni ng in th e tapp ed hole Two example s of hi nged covers ar e sh own in F igs 5 4 and 5 5 Th e cover show n i n F ig 5 4 !s ame p rin ciple as i n F igs 3 0 and 3 6) is h e l d in p lace by a lockin g screw whi le the work is secured by a s et screw carri ed by the co v e r Th e hi nged cove r i llustrated in F ig 5 5 is provided wi th a floati ng s tud that secures th e work the cover whi ch carries the stud being held in place by a n e ccentric binder wi th a hook which slide s under the p in A .

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L AMPI NG

D EV I CE S

13

9

Thi s p rovi d e s a v e ry qu i ck acting j i g Th e lu g B a t th e opp o sit e e nd of the cover p r ev e nts it from s wi n gi ng back too far and br e aki ng the hi ng e F i g 5 6 shows the app li cation of a bell mouthed bushing which is screwed down o nt o t h e hub of a l ev e r ther eby lo cating -

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F ig

56

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F ig

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B

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57

.

e

ll -m ou t h e d

l

S i pon

Knob

S

c e w B u hi ng r

for Cla

s

mping

th e work and at the sam e tim e p rovidin g a guide for the drill whi ch i s to op erate up on it The objectio n to thi s type of bushi ng i s that i t requi res an ex t ra lon g drill an d if made with two S izes of holes as shown particular care wil l have to b e take n in using sma l l dri lls t o prev en t br e ak in g a n um ber of th em .

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40

D E SI GN

An other

obj e c ti o n able feature of this clamping d evi c e i s tha t chi p s work into the threads and prevent turning the bushing easily whi ch also shorten s the life of the thread Thi s diffi culty c an be overcome howev er by not tapping the hole all of the way through as indicated at A ; by counterboring the hole at the top marked B ; an d then grinding the p ilot C an d shoulder D on the bu shing to a snug i unning fit The bushing i s then held true and chip s are excluded from the thread Th e av erage tool desi gner n ever theless avoids screw bushi ng s wh eneve r p os .

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F ig

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58

.

mprove m e nt

An I

on

th e S

cr e w B u hing s

sible but such bu shi ng s are frequently selected after carefu l consideration because of their neat ap pea rance an d eff ective op eration F i g 5 8 shows a clamp i ng devi ce whi ch although a l i ttle more expen siv e than a screw bu shi ng would probably pay for i ts elf i n saving the breaking of drills as the bushing o n thi s jig can be made shorter an d with a one size hole The s crew A swings the lever B abou t pin C an d pu she s down the bushing D whi ch is a s lip fit i n the body of the jig A rather unusual method of d am p ing is illu s trated in F ig 5 7 ,

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D ESI GN

b e tigh tene d in th e fixtur e wi th gr e at rap i di ty F ig 60 shows a spe ci al nu t fo r a box wr en ch the p urp os e of whi ch is to permit li f tin g the wren ch off the h ex an d moving i t back f or a new grip The round p ar t of t he n ut serves to k eep th e wr en ch in p lac e t o b e slippe d back o nt o t he hexa go n nut whi l e th e pin a t t h e top of the n u t makes th e wre n ch a n integral p art of th e fix tur e so tha t it cann o t g e t lost Two unusual examples of jig and fixture de sign are illu s trated in F i g s 6 1 and 6 2 Th e di stanc e that the clamp had to b e .

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A gm t ’ raise d i n removi ng the work from betwe en the V s of th e s e fix tur e s made i t de sirable to provide some method of releasing the clamp more quickly than by turni ng the screw back through the ne c e ssary distance The way in which thi s was a e com li s h e d i s clearly show n in th e illustrat i o n s a n d will be seen t o p con si s t o f loose nin g th e scr ew and then swinging th e block whi ch carri e s the screw o n th e pivot A the dir e ctio n being indi Thi s moves the s crew off its bearing o n c at e d by the arrow F ig

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62

u c k l i Q

r e e a s i ng

.

Cl a

mping

r ran

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e

en

C

LAM PI NG

D EVI C ES

143

th e casting in th e cas e o f th e jig shown in F ig 6 1 whi l e i n F ig The clamp 6 2 th e b in ding screw is r e mov e d from th e clamp shown in F ig 6 2 h as been c ut away at B to permit the point of th e scr e w t o cl e ar it ; a sp ring-p in holds the clamp against th e scr ew a t all times F ig 6 3 shows a hing e d cov e r wi th the clamp at t ached to i t Thi s is a conveni e n t arran geme n t to r emember when consi der ing th e d e sign Of ji g s a n d fix tur e s Th e clamp an d c ov e r are .

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x

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F ig

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63

.

Hi

ng

ed

C ove r

wit h Att ch a

ed

mp

Cl a

h e ld by the S ame p in a n d bo th parts are swung out of the way a t the sam e time by means of the corner of the clamp which ca t ch e s o n th e hing e d cov e r at B The design is such that the fix ture has su ffici e n t clamping ran ge whe n the cover i s held i n p lac e by th e scr e w C The clamp in g is e ff ected by m e ans of th e s cre w in th e cov e r whi ch f orc e s the Clamp do wn on th e work F ig 64 shows a cl amp b eveled a t th e en d to p ul l the work down flush and p ush it i nt o th e V at th e sam e tim e Th e clamp is tigh t e n ed by a scr ew an d a sp ring forces it open wh e n ,

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J IG

1 44

D E SI GN

th e scr ew i s loosen e d Thi s type i s oft en us e d whe n it i s d e si r able to keep th e clamp out of th e way of the cutter Two examp le s of the us e tha t can b e mad e of cams ar e shown .

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F ig

Fi g

.

65

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64

V-b

.

l c k Cl am p o

m Cl amping

Ca

D ic ev

e

i n F igs 6 5 and 6 6 Th e d evi ce shown in F ig 6 5 i s simply an ecc en tri c stud op era te d by a handl e Thi s devi ce p ush e s the clamp agains t the work ; a hol e i s dri ll e d in th e clamp t o sli d e .

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14

D E SI GN

J IG

6

by th e arrow th e work i s securely clampe d an d if ne ce s sary ordinary straps may be added for holding the work When making tool for thin ca s ting of odd shapes it is oft en desirable to u se an adju s table clamp ing device that can be cat e d

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s

s

B

,

INDING S CREW

S I EL ST D W V

F ig

OC ING S D

L

U

.

F ig

.

67

.

68

.

- c ti n u i c k Q g a

Si

mp l

e

F or

m

Cl a

of

mp

of

G an g

S

K

TU

i mpl D ig e

es

n

M illi ng F ixt u

re

easily mov ed out of th e way when reloading the fixture S uch a floating Clamp i s s hown in F ig 7 where the piece of work to be drilled was properly located and clamped with the excep tio n of one arm E for which no ordinary clamp could be B y p ushi n g the supp ort A down a g ainst th e work and u sed .

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LAM PI N G D E V I C E S

1

47

clampin g th e strap B the work is held ti g ht wit hou t springing it ; an d by ti ghtening the nut C t he Clamp i s h e ld i n place by the bun te r an d the work i s s e curely s upported Whe n reload in g th e fixture the clamp i s brou gh t out o f the way by m e ans of the handle D In F ig 7 is shown a s mall cla ping devi ce u s ed when drill ing the riv et hole s through the beadi ng A and the plate B The steel bracket C i s fa s tened by s crews to the s i d e of the fixture The front face of the clamp bracket is u s ed as a s top f or t he p late ,

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C l mpi g D i c f H l di g L g W k and the beading and th e Clam p D with a small h ole drill e d in one end i s fitted loosely in the mi ll e d slot i n the bracket The s e t -screw i s located a l i ttle h ig her than th e hol e in th e clam p and by a few turns o f the screw t he Clamp i s brought down against th e work and f orc e s th e bea di n g up again s t the stop ready to b e drilled S pr i ng bunter s are O ften used i n designi n g fixtures where adjustable supports ar e n ecessary and the form of bunter sho wn in F ig 7 2 has p roved very e ffi cie n t The bun t e r A and t he binder B fit freely in the hole s in the castin g The bunter i s F ig

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69

a

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n

ev

e

or

o

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ar

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148

J IG

D E SI GN

1

J IG

0 5

D E SI GN

wi th th e r e su l t that th e work wi ll f r e qu en t ly be sp rung by th e clampi n g devi c e an d dri lled in thi s p osition whi ch would n a turally spo i l the accuracy of the location of the hole after the work was released from the jig and had expanded back to its normal shape It should b e furth e r born e in mind when clamp i ng rough cast i n g s in a fix tur e that they can be supp ort e d only on three p o i nts and adju s table s t ops should be p lac e d o n the fourth point of the support and also under any weak p ortions of the p iece through which holes are to be dri lled or machining op erati ons are to be perform e d in ord e r to resist the springing action of the cutter P o s t s in which d ampi ng an d locating screws op er ate should be oi liberal p rop ortions an d should not p roject abov e the fixture body an y furth e r than i s necessary i n order to kee p down the tilting action to a minimum ; an d all handle s for clamping devi ce s should b e so located that they will not be awkward to ope ra te i j g,

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CH A P T E R V I I

XAM PLE S O F D R ILL J IG DE S IG N A s j i gs and fixtures are now us e d wh e rev e r machines and t ools are constructed the number of d e signs in use is p ract i call y e nd l e ss although a great many of the s im p ler jigs are con structed on the same general p rin ciple and differ chi efly in regard to form Th e r e are however many di st inct typ es which have b ee n develop ed to handle different class e s of work to the best ad vantage S in ce the jig or fixture is designe d around th e part for whi ch it i s intended the form and size naturally va ry accordi ngly ; but aside from such Changes th e re are many details for in surin g accuracy of locat i on and rapidity of cl amp ing or releasing which give the designer an opportuni ty for the di sp lay of jud gment and ingenu i ty in producing a jig that i s effect ive and at the same t ime not unnecessarily comp li cated and exp en sive In order to i llu strate the relation between the work to be don e and the de sign of the jig or fixture for that work t hi s chapt er and tho s e which follow will be confined largely to illustrat e d d e s cripti ons of de signs tak e n from practic e I n th e obj e ct has b een to show as man y s electi ng th e se d e s i gns typ es of j ig s and fix tures as p os sible I n F ig 1 Dr ill Jig h avin g A u t o m at i c Lo cat in g D e vi c e s i s shown a combinat i on flywh e el and driving p inio n A wh i ch i s to be drilled and tapp ed for four hollow p o int se t screws as shown All th e surfaces mark e d wi th do tte d lines as w e ll as the bor e ar e fini sh e d before the wh e e l com e s t o the drilling machi ne The p roblem was to construct a j i g by which any u nskill ed laborer or boy could drill and tap these wh eel s qu i ckly and correct ly wi thout any pre vi ous layi ng out of the holes The jig had to be constructed so that it would be p ract i cally im p oss ible to make any m i stake in drillin g wh en th e w ork was p roper l y cl amped E

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D E S I GN

jiG

2

The j i g shown in F ig 2 fulfill s all t h e s e co n diti o n s and gives very good re s ults It con sists of a cast i ron angle p late base B which is fastened u p on the dril ling machin e table A bracket C n k fi l li s r t e head screw s is fastened to this base by countersu This bracket wh i ch i s of U shap e is provi ded wi th a stud L fitting into th e finish e d bore O f whee l A The two arms of the U sha p ed bracket serv e as su pp orts for t he dril l guides M A t one s i d e the pin P passes throu g h bracket C w h i le the oppo site side of C i s p rovi ded wi th an indentat i on to r e ce ive the pin N wh i ch con ne cts the drill gui des M P in N i s held in .

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mbinati

Co

Fig 1 .

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on

y h

Fl w

ee

l

and

Di

r ving

Pini on

plac e by he adless set screws S which also hold the dr ill gu id e s to pin P as shown One end of pin N forms a handle by means of wh i ch the guides may b e conveniently swung out about pin P as a fulcrum B racket C fits tightly between dr ill guid e s M a t both end s thus holdin g th e m firmly in p la ce A scr e w 0 having i ts c e nt e r located som ewha t above the center of p in N pr eve nts this p in an d also th e drill gu i des from comi n g u p wi th th e drill and breaki n g the l atter B racket C i s provi ded wi th a slot in wh i ch sl i des a rack D a detail Vi ew of whi ch i s shown at Y whi ch is provi ded with teeth of the s ame pitch as thos e in pinion A that are cut before the wheel com e s to the drilling -

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J IG

54

D E S I GN

hold the drill and tap Th e whe e l is now r evolved causing the rack the t e eth of which m e sh wi th those of the p in ion to move unti l the sto p pin E t erm in ates i ts motion at p oint G The wheel will then have turned 3 5 degr e es an d i s ready for the drilling and tapping of the other two holes A fter thes e are fin i shed the wheel is turned back u n ti l stop p in E Comes agai n st po int F The operator cannot t ake the wheel off nor .

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F ig 3 .

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J i g for

H l d ing C o

i

as t - r o n

B l ck whi l d illin g o

s

e

r

p ut i t o n until th e rack is in the correct starting positi on b e cause s af e ty latch H wil l be lift e d by rack D thus p r eve n t ing the pinio n which just p asses i t wh en in th e l ow e st p osit i on from bein g taken off or put on The operator must therefore start at the proper point for turning the full 1 3 5 degree s and can n ot make the mi s take of n ot turning the wheel back far enough to ach i eve tha t r e sult -o e rat e d C l am in Cam i l Two j i gs w e re li n D r i l S d e o p J g p g re quir e d for drilling blocks of the S iz e shown at A in ,

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F ig

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3

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The s e block s were of gray iron and when received ,

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D R I LL

i G s j

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were machined ll o ver and accurate wi thin inch Th e drilling was performed in two operati o n s ; the two % inCh holes a n d the i inch hole we re drilled simultan e ously in the firs t operation the { inch hole b eing dri lled in the s econd operation Thi s order of drill ing was nec e ssary as the g in ch drills would have been deflected by cutt ing i nto th e lar ge r hol e but the { inch drill having a large r di amet e r was not affec te d by cutting into the s maller holes The first problem was to design j i gs for holding the blocks that would require the minimum amount of tim e in loadin g and unloading A t B is shown the jig tha t was us e d successfully for dril lin g the inch hole It i s similar in d e s i gn a n d ope ra tio n to th e one that was used for drilling th e two g in ch hole s and the i inch hole The jig con si sts of the cast i ron body C whi ch is set on legs five inches hi gh in order to p ro vi de han d room for using th e handle D an d also t o give a sharpe r angle to th e dis charg e chu te E a n d at the same t im e to provi d e cl e arance for t he receiving box a t the e nd O f th e Chute The s lide or movable jaw F i s made a clos e S l i ding fit in the body C and i s held in p lace by p i eces G J aw F carri es at th e forward end th e hardened wearing p ie ce H a n d th e t emp let K for gu i ding th e drill the t emp l e t K b eing attach e d to the movabl e jaw in thi s cas e to allow great e r freedom in loadin g S li ding jaw F i s clos e d up on th e w ork by the mo vement of the c am I which i s of such shap e as to gi v e a p owerful g ri p to the jaws a wi de loadin g space a n d a qui ck moveme n t Ten s i on sp rin g I holds the sli d e back l e avin g th e jaws always in a n op en posi tion excep t wh e n forc e d to ge th e r by means of p res s ur e exert ing o n the hand -l ev e r D A carbo n st e el locat i ng p i e ce L i s dowe l e d t o t h e body to r e c ei v e the blocks ; i t is aC Th e block when c ur at e ly lin e d u p wi th the hol e i n te m p l e t K in place rests on a half floor extendi n g across and in front of the o penin g in L Just in front of thi s i s the large o p ening into whi ch the blocks fall and b eneath whi ch th e chut e E i s p lac e d A li ght s p rin g not shown kn ocks th e b lo cks O ff into th e o pen in g when the slide F is wi thdrawn and th e y slide down the Chute into the recei ving box It is only nece ss a y for th e O perator i

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to place th e block in the j i g an d f ee d the drill to the work B rushe s are unnec e ssary as the Chip s clear themsel ve s and th e blocks are fr ee d from chi ps as they slide o ver the perfora t ed section of chute E F or drilling the three holes in the sides a multiple dri ll head is us e d and the piece i s held in a jig which is a duplicate of the one S hown except that the templet whi ch gu i des the drills is .

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S EC ION X X

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Ma c h i ner y F ig 4 .

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J i g for

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ing whil d illing r

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attached to t h e stat i onary jaw an d is pro vided with thr ee hol e s for gui ding the three dri lls i for ri l n n g The sho n in i D l i Ri F at A and w B 4 J g g j g g i s used for drilling the ring shown at C R eferring to the illus t rat i on at B i t wi ll be seen that there are three plung e r s D held against the con i cal point of wing screw E by S prings F In operat i on the wing s crew E i s turned back un til the plungers The ri ng C is then D are just wi thin the body G at po in ts H s lipped on and the wing screw turned down until the plunger s D are forced out and in to contact wi th the in side surface of th e ring The ring i s then drilled on a sensiti ve drilling machine Ind e xi ng J ig op e r at e d by H and l eve r and F oot-t r e a d l e The drill j ig shown in F ig 5 was designed for drilling four angular holes in a bras s time fu s e cap !S e e s ectional view of The principle of thi s j g can cap at lower part of illu s tration ) .

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one end of whi ch is round e d and engag e s with th e n otches in the index plat e B ack of th e pin and held in p lac e by a headless set s crew K i s a co i l sp ring J whi ch ho l ds th e lockin g p i n against th e in d ex p late The t en si o n of thi s S pring is just enough to hold the work from turning whi l e be in g dri lled but not enou gh t o p r e vent i ts b eing r e adi ly in d exed by a qu i ck pull on the indexing lever The work is held in p o si t i o n aga ins t th e l ocat ing p l ate A by the plunger L whi ch r e sts on a s ingl e in ch hardened ste e l .

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ball that acts as a b e ar ing while the work i s bei ng index e d P lunger L is carr i ed in a second plunger M wh i ch i s held u p by a powerful coil sp ri ng N This spring should be l onger and stiffer than the o ne shown as an e normou s p r e s sure can b e obtained with drills as small as the N o 3 0 used wi th thi s work The outer plu nge r M i s op erated by a foot -t r e adle co nn ected to the lever 0 I n operati on th e foot treadl e i s depressed and a piece of work i s plac e d betwe en the plung e r L and th e locating plat e A Wh e n the treadle is released the work i s held by the tension of the spri ng N whi le th e i ndexing i s done by t he lever E The locating plate A has slot s milled in it .

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wi th a radi u s cutter of the sam e ra d ius as th e dril l t o be us e d Th i s fe a ture in co nn e ction wi th th e lip o n th e work a n swers the sam e purp ose as a dril l bushi ng no other m e a n s of guiding th e drill be in g n e c e ssary Th e p ro duct ion of thi s j ig was about 4 000 ca p s per day s i v i r n e m b e i n L v r r n l i M r h a e e n d S O e a t e d C a m a g g p J g p p g — The jig shown i n F i 6 is us e d for dr i l l in g 0 in ch hol e s g 5 in th e motor truck steering arms shown in F ig 7 Owi ng to the means provi ded for securi ng work in thi s jig ready to be .

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dril led and for releas ing th e fini she d p ar t aft e r t he op erat ion B ushin g ha s b ee n p erformed t hi s i s kn own as a pum p j i g A i s be ll mouth e d on the low e r sid e a n d dro p s d own over t h e top of the boss at the end of the steerin g arm The t hread e d en d of th e wo rk i s sup ported by m e an s of a s l otted block B car ri ed a t th e e nd of bracket C Wh en it is d e sired to se t u p a pie c e of work in t he j i g p ump ha ndl e D i s p ush e d down ; thi s handle swin g s o n pivots E wi th the re sult tha t rods F ra i s e jig bushing A against th e p r e ssure app lied by coil springs G The piece of work is th en S lip p e d in to place a n d handle D i s rel e as e d so t h a t s p r in gs G apply sufficien t pressur e to enable bushi ng A t o hold th e work in th e desired position to be drilled Thi s arrang ement wi ll be ,

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rea di ly understood by comp aring the j i g wi th the work After the drillin g o p eration has been completed it i s a simple matter to relea s e the work from the j i g by pu shing down the handle D and withdrawing the piece from under the bell mouthed bushi ng The drill j ig s hown in F ig 8 was D rill Jig for F or k L inks de signed for drilling fork links The form of these link s i s indicated by dot and da sh lines in both views The link h as a round boss at one end and rounded forks at the other end It .

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accurately held between two V block s one being adjustable and the other stat i onary The adjustable V block A is clamped against the work by the star wheel and screw shown and it travels between fini shed ways thus provi din g an accurate as well as rap id method of clamping These V blocks have inserted steel plates B and C The latter which is in the s tationary V block car ie s a drill bushi ng for drilli ng the lower fork and an upper shoulder on t hi s plate provi des a support for the upper fork ; thus there are two bu shi ngs i n alignment for drill ing the two end s The in s erted plate B in the ad j u s table block supports the oppo s i te end of the fork link With thi s arrange -

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flat of the work and then tapping it lightly the j ig i held s ecurely in place When drilling one of these half holes it i s found that if an or di nary twist drill is u s ed there i s a tendency for it to hog in which is likely to re sult in breaking the tool ’ F or thi s rea s on it i s de sirable to u se a s traight flu t e d or farmer s drill although good result s may also be obtained by grinding a twi s t drill i n such a way that i t h as no rake or hook re sult ing from the spiral form of the flutes A drill which is ground in thi s way pre sent s a s quare or slightly obtu se cutting edge to the work thu s doing away with the trouble experienced f om d ill breaking when ground in the u sual way ,

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drilling t h e hole the work is set up on end on the drill pre ss table and the drill is fed th ough the bu shing in t h e u sual way the bu hing ho ldi ng the drill in po sition until it s tart s to cut A s the drill i s fed down there i s a tendency to force it away from the work but thi s tendency is re sis ted by the hardened stud A so that the half hole i s drilled parallel with the axi s of the work Thi s jig a fford s a convenient mean s of quickly accompli shing thi s work and having the two half hole s match up accurately so that no di fficulty i experienced in as sembling the work v e havi g o ers u o n whi h i is ur ne d o r The box n c t t R c k p Jig drill j ig shown in F ig was u s ed for d illing three hole s in a certain piece that was to be produce d in quantity The j g is ,

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made from a forging two stationary bushi ngs b ei ng i n serted in the top and one in th e bottom A s the jig and work weighed about twelve pounds i t was hard for the workmen to be con s t ant ly lifting the jig and turning it o ver for the o pe rat i on o n the other side ; therefore two p iec e s of st ee l we r e mach ined to a radiu s and attach e d to th e j ig be twe en the four fe et on the s ide oppo s ite th e lea f With t he a i d of these rockers the jig They do not i s ea sily turned ove r f rom on e s i de t o the other interfere in any way wi th the worki ng part s and when changing ,

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F i g 11 .

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D ill J i g d r

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work the j g i s supp orted by the rock e rs In thi s way the j g i s always on the dril l ing tab l e and there i s l e ss l ikelihood of the op erator l ett ing i t fal l to the ground or throwin g i t down and snappin g the bushi ng or le gs whi ch are harden e d to glas hardn e ss I n addi tion th e op era t or does not have to work so hard and the p roduction is consi derably increased D r i ll Jig d e s igne d for R api d In d e xin g The necess i ty for a drill jig of the indexi ng typ e was brought about by a cert a i n desi gn of motorcycle dri ve pulley Thi s pull ey is of t he flat belt flanged type having co k in s ert ov e it entire periphery i

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i s shown a completed pulley wi th the To the ri ght in F ig cork in sert s in place M ounted on the drill j ig i shown a pulley being drilled The pulley i 4 5 inches in diameter and has 4 2 hole s 5 inch deep arranged in three rows of 4 equally spaced around the p erip hery The drill j ig is built in such a manner that it will take a large variety of sizes o f pulleys A t the left of the jig is s hown a larg e drum whi ch serves as a means of indexin g the d ill j ig readily and has three annular groo ve s on its periphery spaced the s ame d i st ance ap ar t lon gi t u d inally as it i s desired to ha v e the hole s drilled on the pulleys D irectly in the center of th e se groo ves and spaced equ i di s tantly around the p eriphery are 4 tapered index pin holes A t th e base of the dri ll jig is an index pin !not S hown) which i s tapered on the end to fit the tapered index hole A t the back of thi s index pin is a light S p ring which holds it con s tantly in contact with the index drum In operati on the firs t row of hole s i s drilled When enough pre ssure is app lied to the drum to rotate it the index pin being correctly tape red will jump out and allow the drum to r evolve to the next i ndex hole A fter the firs t row of hole s h as been drilled in thi s manner the s econd row is placed i n line wi th the revolving drill by forcibly s li ding the index drum and i t s shaft longitudinally until the index pin jump s into the mid dle groove In thi s position the 4 central hole s are drilled as before To drill the las t row of holes it is only n e cessary to move the index drum over as in the second c ase Where i t is essential to drill holes accurately spaced around th e p eriphery thi s form of index drum and pin might not b e accurate enough H owe ver in t his case and in many other cases i t i s sufficiently accurate It h as the advantage of being qui ckly index e d whi ch is not always true of the ordi nary index pin that has to be grasped by one hand while the other hand is employed in rotat ing the fix ture In thi s case the right hand i s n ever moved from the drill sp indle le ver The In d e xing J ig pr ovi d e d wi th W or k lo c a ting D e vi c e f i i hown in 2 s for drilling di ferential s pider arms i F s g j g B efore the drilling O peration the forging i s chucked and rough 11

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tud D In order to locate the spider c entrally in th e j i g tha t is so that the arm s will come in average alignment with th e four bu shin gs the centering device E is emp loyed B y mea n s of a spring F the e nd of which i s attached to the bent end of the part E the two aligning fingers are brought to b e ar S imul s

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again s t oppo site arms of th e spi der thus locating the spider in a central po sition i n the jig A fter thi s i t is a s imple matter to drill and countersink the spider arms o n e after another indexing the j g by hand for each arm A n idea of the facility with which thi s j ig i s operated can be gat hered from the fact that 5 00 of the s e pider are drilled t ane o u sly

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and cou nt e rsunk i n a day of nin e hours maki ng a tota l of 2 000 hol e s per d ay The most impo rta nt part how eve r i s th e fac t that th e m et hod insure s that th e c enterin g is do ne wi th r e fer e n c e to th e hard e ned sp ider arms thus in suring that th e amou nt of m eta l r emoved in grinding will be p ract i ca lly e qual a t all po in ts — Ind e xing Jigs mount e d on Trunnions A box dri ll j i g for us e in drillin g r e am in g tapping chamf e ring a n d sp ot facing hol e s in automobil e r e ar-axl e hous ings is i llustrat e d in F ig 1 3 ,

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It wi ll b e s ee n from the illustratio n that th e j i g swi ngs on tru n nion s fitted in the cradl e or bas e a n d th a t t he base i s equipped wi th i ndex pin s for locat ing t h e j ig in an y of five p ositions The r e i s a n in d ex pin at e ach s i de of th e base and th e s e pin s are op erated s imultan e ously by a S ingl e ha n d l e ver The r e ar axle hous in g i s p ut in th e ji g through a n open ing covered b y a h in ged an d latched l i d ; and the work is held in plac e by m e an s of hardened steel plugs whi ch insure p ositive locat io n All p arts of the j i g which ar e subject to w e ar are hard ene d a n d grou n d to size thus gr e atly reducin g th e po s si bilit y of i naccuracy o f th e work as a resu l t of wear The weight of the j i g is and it is equipp ed with rollers carried 0 pound ,

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by hardene d and ground steel pins These rollers run on tracks whi ch carry the j ig under the machi ne and also enabl e it to be ea sily run back to remove th e work It i s necessary to drill quit e a number of hol e s in the castin g shown in place in t h e jig illustrated in F ig 4 an d the s e holes .

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D i ll J ig f Y k E d ar e locate d on different si de s and at various angles to one anoth e r F or t hi s reason an i ndexing jig is employ e d Thi s particu lar illustration shows the cover A of the j ig removed in order to illustrate more clearly the position of th e ca st i ng whi ch i s located in the j ig by it s trunni ons The ma in body of F i g 15 .

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F ig 1 6 show s a j i g for drilling and A Vi s e Dr illi ng J ig milli ng an elon gated hole in a p iece of work wher e the limit of —

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in ch A flanged accuracy r e qui re d is not less than mil ling machine Vi se was fitt e d wi th a spe ci al j aw havi ng a P in C was put in to V groo ve c u t lengt hwi s e as shown at B i

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Vi D ill J ig with S wi li g L f f F mi g O bl g H l a soft jaw on the movable s lide of the vise and located so that th e m il led surface of shaft A would rest on the upper surface of the pin and hold the shaft level for drilling B ushing plate D was n ext p ut o n a n d h e ld in plac e by a cap s cr e w E B ushin g plat e D was th en lai d out and dri lled a n d reamed i n positio n for th e locat ing pin F an d the dri ll and cou nterbore bu s hings G The s top pin H was locat e d in the bu shing plate D to in ure F i g 16 .

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obtainin g the right locat i o n of the dri ll e d hol e from the e n d of th e shaft A A fter th e ho l e was dri l l ed the locat ing pin F was p u ll ed out a nd t he p late D swu ng arou n d from the first p os i t i on as sh own by th e dotted line s to the s e co n d p osi t i o n a n d pin F was ih E ach ho l e for pi n F was loca te d so as se r t e d i n a n oth e r hol e to bring th e bushi ng p late D in to the p rope r p osi ti ons for dril l in g a n d coun t e rbori ng A spe c i al count e rbor e or m i ll was t h e n us e d through t h e bushi n g G to el o ng ate the ho l e t o the p rope r s ize and d ep th Thi s counterbore was mad e from drill rod of th e sam e diam e t e r as th e wi dth o f t he e l on g at e d slot in the shaft F our t ee th we r e cut in the en d a n d i t was th en hard ene d a n d t emp ere d A ft e r the shaft A was p r ope rl y dri ll ed a n d cou nte rbor e d i t was rem o ved from th e vi se an d th e bushi n g p late D swung back in to the dr il ling p os i t i o n ; t hi s also bring s th e stop pin H in to po s i t i o n for locat ing t he n e xt S ha ft An other sha f t i s n ow p u t int o t h e vi s e a g a in st t h e sto p pin a n d the p revio us o pe rat i ons are repe at e d Thi s d e vi ce has be en us e d wi th new bushing p late s to sui t many di ffe r en t kinds of wo rk F or dr il ling a n d tapping when using a r eve rs ib l e t appin g chuck o r a drill p r e ss tha t has a r eve rsibl e spind l e i t wi ll b e foun d to b e a ve ry h andy t o ol A ft e r th e ta p h ol e i s dri ll e d in th e w ork pin F i s p ul l e d out a n d bushi ng p la te D can b e swung ou t o f th e w ay f i D i l li n D e H o l e s i n t u d s Th e j ig to b e d e o r e S r J g g p s cri b e d was des ign ed for dr i l l in g brass studs whi ch w e r e t urne d from a g in ch squar e bar w i th a S hort sect i o n of th e origina l squar e bar left at th e c ent e r of th e fini sh e d stud Th e drilling o pe rati o n could n o t b e do n e c o nven i ently on the aut o mat i c scr ew machin e as i t was n ecessary t o drill a 5 inch hol e t o a d ep th of 2 2 in che s Th e machi ne us e d i s a spe ed la the w hi ch i s p rovi d e d wi th bo t h wh ee l and leve r f e ed for the tai lstock F or thi s work th e ta il stock spin dl e was remove d an d rep lac e d by a spe cia l s pin dle whi ch i s shown at A in th e cross-s e ct i onal View F ig 7 In th e i llustrat i on i t wi l l be s ee n that th e sp in d le i s provid e d .

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with a threaded nose on whi ch the bracket B is screwed The spindle was bored out to such a size that the work holder C is a sliding fit in the spindle the mo vement of the work holder being accompli shed by means of the le ver D which is pivoted to the bracket B The quadrant E is pro vided with teeth for the purpose of locking the le ver i n the closed po sition One of the s tuds to be drilled is s hown in po s ition at F in the work holder It is accurately centered between the tapered drill bu shing G at one end of the work holder and the tapered end of the rod H at the oppo site end of the holder The drill .

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D illi g D p H l i S t u d bushing is pressed into the end of the work holder and the de sign of the work holder and the manner in which the rod H In i s thread e d into t h e tailstock screw are all clearly shown setting up a piece of work in the jig the rod H i s held stationary by it s threaded connect ion with the tail stock screw and a movement of the lever D r e leas e s or re centers the work by sliding the work holder C in the spindle A the work holder being prevented from turn ing by mean s of a clamp J which engage s th e square which is left at the center of the stud The drills u s ed for thi s operation were of exceptional length and made with an increase in the angle of twi st They were held in the lath e spindle and the work was fed up to the drill by means of the tailstock le ver The u se of this lever feed made pos sible the quick return of the work whi ch enabled F i g 17 .

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75

th e work is such that i t must b e located in mor e than o ne dirc e t i on a n d clampe d a t s eve ral p o in ts If th e ne c e ssary clamp s could b e p osit i vely o p erated by a S ingl e le ver th e gr e atest possible sp eed w ould be obta in e d but this i deal co n di t i on may n o t b e p ract icabl e owing t o the fac t that the hol di n g p osi t i o n of e ach clam p is l ikely to vary wi th th e siz e of the work t hus making an y combine d p osit iv e moveme nt of th e clamp s ine f fe ct ual Th e clamp s may b e r e l e as e d by a s in gl e l e ver bu t wh en ho l d ing th e w ork thei r pos i t i o n is fixed by th e work i ts el f and thi s con d it i o n coupl e d with vari atio n s in the size of th e work .

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F i g 20 .

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W ork

t o b e d ri

ll d in J ig s h wn in F i g e

o

19

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mak e s th e o p eration of the clamp s by a single lev er a d iffi cu l t mat te r If it w e r e always p ossible to reve rs e thi s condition maki n g each clam p ind epen d e nt of th e o t hers in i ts closing moveme n t an d thus com pen sat in g fo r varying s iz es of work a s ingl e l eve r mi gh t b e arrange d to r el e as e all th e clam p s a t o n c e Thi s d e si rabl e r e sult has be en accomp l i sh e d i n the jig shown in F ig 9 by emp loyi ng sp rin g p r e s sure to clos e th e locatin g an d hold ing m e chani sms The p o sit i on o f the work i s fix e d in two di re c t i ons a n d the wo rk i s clampe d at two po in t s by a S ingl e move m e nt of th e ope rat ing l e ver to the right whil e movi ng t hi s l ever to th e l e ft re l e as e s th e work from the clam ping and l ocatin g d evic e s Th e work !w hi ch i s shown o n a r e duced scal e in F ig 2 0) lies on three harde ne d st ee l blocks A and is locate d b e hi nd pins B moun t e d in th e se blocks an d to the left of the pin C i n the base of the j i g Th e block D forms a s e at for th e cove r plat e and th e l a t ch whi ch holds t h e cove r-p lat e down i s pivot e d in thi s block Th e lat ch is he ld down by a sprin g p lu n ger The be llcrank le ver E .

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whi ch carri es the fourt h locating p in is pivoted to the base of the fixture and pro vided with a lug which en ters an op ening through the ba s e and receives the pre s sure of the spring plunger F Th e bracket s G are attached to the bas e of the fix ture and the cover plate is hinged to these brackets Th e brackets are al s o bored out to receive two sp ring plungers The ope rating le ver is fastened to a hub H and a link I is pivoted on thi s hub th e oppo site end of th e link being att ached to the hub J The screw s whi ch hold the op erating le ver to the hub H and the link I to the hub J ar e exten ded to form p in s which engage the l ever s K The jig is shown closed wi th all parts in th e p os itions th ey would occup y when holding a piece of work To rais e th e cover p late the latch is p re s sed back when th e thrust of a spring p lu nger rai s es i t su ffici e ntly to p re vent the latch r e engaging the co ver plate Th e cover plate i s ra i sed to th e l imit of its movement which is a few degrees beyond the p e r i s then swung to the left until The operat i ng le e r i l r v n d u a c e p it s trikes a limit pin Thi s mo vement of the lever turns the hubs H and J bringing the pins again s t the tail ends of th e leve rs K and compres sing the springs behi nd the plungers carried in the bracket s G Thus the end s of the le vers K whi ch engage the work are swung back relea sing the i r grip The final movement of the left hand lever K brings the ad s u s t a l v b stop screw carried by thi le er aga i n t a lug p ro e L s j i n e c t above the le v er E thus compres s ing the spring F j g and relea sing the work from the pre ssure of the p in carried by the lever E The s crew L limits the mo v ement of the lever E to the m in imum amount nece ss ary to release the work and the stop s crew may be adj u sted to accompli sh this after the jig has been locked open A fter removin g the work from th e jig an undrilled piece i s placed in po sition and the ope rating lever thrown to the right T his cau se s the different holding members to go through the i r sequence of movements in the oppo site order to that described for relea s ing the work from the jig The re sult is that the work i s clamped in place in a minimum amount of time ,

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DE S I GN

is in d ex e d to the p ositi on shown in F ig 2 2 Whi l e in thi s position 2 2 hol e s are drilled in th e crankcas e a n d after th e s e ar e compl eted the mil ling i s do ne The millin g attachm en t for this drill jig con sist s of two m emb e rs D and C P art C con si sts of a body member for the millin g at t achmen t I n th i s memb e r ar e cut ve rtical ways in whi ch th e cutter carryin g m emb e r D trave l s u p an d down The movable m e mber D carrie s a horizo ntal cutt e r arbor having a gang of thr e e cutters J an d G on each e nd In the center of this arbor is a bevel gear whi ch m e shes with an oth e r b ev el g e ar carrie d by a vert i ca l i j g

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Fi g 22 .

J i g in

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P

o s iti on

for

D i lli r

ng and

M illing O p e

rat i ons

sha ft th e u ppe r e nd of which t e rminates in a M orse ta p er shank E The movable m ember D is held normally in the upp er p os i t i on by s p ring s I n o pe rat i o n the dri ll sp indle i s brought down in co n tact wi th the t ap er shank E unt i l i t is seated i nto the ta p er dri ll socket Th en th e drill spindle i s rotated and the mil l ing arbor of course rotates also through the b evel g e ars The dr ill spin dle i s fe d down ward the sam e as f or drilling a n d i n so do in g the en t i r e m e mber D is low e r e d unti l the ri gh t hand set of cu t t e rs G i s brought in to con tact wi th th e boss to b e m il led a t th e ri ght han d side of th e crankcase Th e cutt e rs continue t o b e low e r e d u n t i l they com e aga i nst a p r e vi ously s e t stop i n wh i ch p osi ti on t h e m illing of the right han d bo s i complet e d ,

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To p roc e ed with the m il l ing of th e left -hand boss it i s ne ce s sary to l o os e n the strap s that hold the milling fixture i n place grasp the han dl e s H and li ft th e mill in g attachmen t o ver to th e l e ft hand si d e of the dri ll j i g where there are dowel pi n s whi ch accurately l ocate i t i n i ts corr e ct r e l ati ve p ositi o n The ope rat i on i s rep eat e d in th e same way as for the right han d boss exc ep t that cutters J are used in s te ad of cutt e rs G This milli ng at t ach m ent i s n eve r remo ved from th e drill ji g except as exp la in ed for m illing th e right and left han d bosses The movab l e member D is mo ve d up ou t of the way by sp ring p res sure wh en a new cra nkcas e i s be ing p laced in the jig It would b e p ossi ble of course to equip thi s drill j i g with two m il ling attachm en ts on e at e ach end so that i t would not be nece s sary to mov e t he attachment from one S id e to the other but as the ch anging of the fix t ure from one S i de to another was such a S im p l e matter i t was not de e med ad visable to go to t h e extra expen s e that thi s would invol v e i n s i C r rillin P is o The shown in s f o r o s d t F ig 2 3 g J g j g i s us e d succe ss fully in cro ss dri lling pistons Th e piston is drilled from both s i d e s and not all th e way through from one s i d e which i s th e common p ractice e specially wh e n the work i s done o n some k in d of lath e It i s n o t an easy matter to drill a n d r e am a true hole by starting on one s ide of the pi s ton dril ling through one bo s s and then advancing the tool acros s th e o pening between the boss e s and exp ect ing the tool to secure a true start i n the s e cond boss Thi s jig was made in the follow ing manner to insure accuracy A block of cast i ro n was milled squar e and the large hole rough bored t o withi n T g inch of s iz e Thi s block was then milled across one end to receive the stop -bar A A fter fitting the stop-bar i t was removed and th e seat for th e clamp bar B was bored by using a fly cutter i n the milling machi ne This clamp bar was a p i ece of two inch cold rolled stock m illed D uring the suc fla t to form a little more than a half rou n d c e e di ng bori ng and grinding operations th e clamp bar was held to it s s e at by the two screw s C which had wash e rs under their h e ad s in s tead of the springs S hown in the illu stration A p iece ,

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D E S I GN

I J G

of in ch stock was placed betwee n th e c l amp bar a n d s ea t whi le borin g and grinding ; t hi s s him was take n out la t e r to allow for a little clearance A fter the clamp bar was fitted and bored the holes for the hardened bushin g s D were bored and the bu shing s fitted The s e bushings were long enough to reach through the large bore so that they could be ground flush with the in side of the jig The jig was next se t up on the table of a H e ald cylinder grinder and the holes in the bushings ground in l ine and true -

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F i g 23 .

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J ig

u df se

or

C

d

r o s s - ri

lli ng

P

i

s t on s

to s ize The j i g was then placed on one side with the bush ings in a horizontal plane and the large hole fin i shed to s ize by grinding To be sure that the hole s in the bu shings would be perfectly central wi th the large bore an arbor was groun d to a snug fit for the bu shin gs and the large hole was gaged from it m e asurin g from the wall of t h e large hole to the arbor until both side s were exactly the s ame The hole was then fini shed inch la ger than the pi ston to be worked on Two sli p bu s hings E were made to fit the bushings in the j g .

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a p air of jaws bored to the p roper s ize to fit the piston to be worked on The sp rings o n the up right studs h o l d up the upp er or clamping jaw whi le the work is being put in or take n out In op e ratio n a pis t on is slipp ed between the jaws th e fac in g bar run down through the cro ss drilled holes the cutt e r fitted into the bar and the to p j aw set by a half turn of the lever hand l ed nut A feature of the facing bar i s the mann er in .

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B which the cutt e r is h e ld It will be s e en that the cutt e r h as a half round notch in the c en te r of th e bottom e dge that r egisters with a steel ball L in the center of th e cutter s lot A s t iff sp rin g holds th e ball to it s sea t in the bar The cutte r is also provided wi th two hole s near each end that are u s ed for pull ing i t out of the bar with a s tout wire hook It i s double e dged so that both bo s ses can be faced wi thout rever sing i t or stopping th e machi n e Thi s method of holding the cutter would n ot be de sirable in the ca s e of a boring tool but for a facing tool i t s e rv e v ery well O f course the cutter mu s t be a ni ce fit in the F i g 24 .

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J ig

u df se

or

c

F a ing t h e Pi st on

os s e s

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D RI LL J I GS

1

83

bar Whe n t he facing j g is used it can be clamped to th e machine table while the cros s drilling jig is not clamp ed b e cau s e it i s necessary to turn it over and over Unive rs al Jig s While a large perc e ntage of th e j i gs in common use are designed espe ci ally for some part a n d ar e used exclu sively for that particular part occasionally j igs are so constructed that they are adju stable and adapted for a variety of work F o this reason they are often called un iv ers al jigs Jigs of this typ e may re s emble an ordinary j g som ewhat i

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D i ll J ig and s imply b e arranged to locat e th e gui d e bush ing s !in the case of a dr ill jig) in differe n t p os i t i o n s ; or th e j ig may b e in the form of a sp eci al a t tach m e nt for th e dr illi n g mach in e An e xamp l e of un i v e rsal jig co n struct i o n i s shown i n F ig 5 This i s a very s im p le design and cons i sts of a p lat e conta ini ng o ne or more dri ll bushi ngs and adjustabl e loca tin g rods It may be used for accurately locat ing and dr il lin g hol e s in j i gs d i es and temp lets A hard en e d and ground block A i s pro vi d e d w i th four sl i d i ng p in s B a s e t of removab l e bushi ngs C and eigh t headl e ss s e t screws B us hi ngs C may be mad e u p with vari ous sized holes to provi de for gu i ding different sizes of drill s S mall S lugs of brass or copper are used between the set screws and the pins B so that ad j ust ing th e scr ews wil l n ot tend to change the position of the p ins F ig 25 .

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m ak

Tool

e rs

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U ni ve r s al

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T0 il lustrate the us e of thi s j i g suppose t ha t a number of holes must be accurately located drilled and reamed in a di e block A fter the block h as been p lan e d up p erfectly squar e p arallels are clamp ed to the edges so tha t they overhan g in the manner shown i n F ig 2 6 allow ing the pin s B t o enga ge with these p arallel s when the jig is laid fla t again st the die block The bushin g C is located at a known di stance from the e dge s of the j ig a n d by s etting the p in s B in the required po sition by means of a micrometer or m i crometer depth gage ,

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F i g 26 .

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M th d e

o

of

u ing U niv

e r s al

s

D ill J ig h w r

s

o

n

in F i g 25 .

the bushi ng i s located in po sition for drillin g the hole in the di e block F or thi s purpo s e the j g i s clamped to the die block wi th a pair of p arallel clamp s after whi ch the hole i s spotted dril led and ream e d in the u sual way It will of course be evi dent that any number of holes that come within the range of the ji g can be located on the di e block in the same way The useful ne ss of thi s tool wil l be apparent to any toolmaker and many uses wil l be found for it that may not be s een at the first glanc e A uni versal jig whi ch is in the form of an attachment whi ch i s clamped to the table O f a drilling machine i s shown in F ig 7 The dri ll bushing is in l ine with the axi s of the machine spin dl e so that holes may be dr illed as in the ca e of an ordinary jig and there is a compound table with slide s at right angle s which .

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ment to l oca te an y n umber of ho l es in th e work in th e desired relat i on to each oth e r as th e table sli des may b e mani p ulated and fin al s e tt ing s ma d e wi th the mi crometer h e ads and d i s tanc e bars so t ha t each ho l e i s l oca te d in the p ro pe r relati on to th e p r e cedi n g ho l e C lamps are p rovi ded to l ock the t ab l e in e ach p os it i o n befor e th e drilling operat i on i s starte d Th e di stanc e bars ar e supported by bushi n g s hel d in V shaped s e ats whi ch su pp ort them at th e proper hei gh t to line up properly b e twe en the micrometer spindles and stops o n th e tab l e whi ch com e in contact with th e micromet e r spindl e s ,

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F i g 28 .

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Vi

se

wit h J i g

Att chm a

e nt

whe n the t ab l e i s se t in th e z ero p os iti on J ohan sson or oth e r gages may b e us e d in p lac e of the di stanc e bars i f so d e s ir e d — il n s f D r i n T e i g i h e mac ne V i ses A c h m t o r l n V s e s hi tt a Jig s uch as ar e us e d f or m illin g or p l anin g o pe rat i ons ma y b e used for drilling when th ey ar e p rovi d e d with at tachments for h old ing dr ill bushings or l ocat ing st op s Th e r e ar e n ow o n th e market Vi ses furni sh e d wi th j ig at t achments r e ady for us e O ne of the s e Vi ses i s il lus t ra te d in F ig 2 8 where it will b e see n tha t a s t o p A may b e used t o l ocate th e work whil e the bracke t B ho l ds th e bushin g whi ch gui des the dri ll A S a Simp l e i llustrat i on of th e p rin cip l e in vo l ve d in us in g a jig of thi s type ref e rence is made to F ig 2 9 in whi ch the part be ing machi n ed is a round collar Thi s collar A i s grippe d aga in st a ve e in th e s o li d j aw and the bracket conta in ing th e .

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F i g 29 .

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Vi

se e

qui pp

ed

Att chm C ylind ic l P

wi th J i g

a

r

F ig 3 0 .

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D illi r

ng

lH l

S e ve ra

o es

a

wi t h

187

e nt and

b lo V—

ck

s

for G ri

ppi ng

ar t

a

Te

m pl

ch d t

e t att a

e

o

Vi

se

1 88

I J G

D E S I GN

bu shi ng B i s adjuste d to t h e correct p osition for guiding the drill into the work It i s clamped in p lac e on the solid jaw by means of bo lts C To op erate the jig the movable jaw is open e d and a pi ece of work inserted in the V block ; then i t is only nece s sary to tighten the jaws and proc e ed to dr ill In thi s way duplicate parts are obtained without an elaborate j ig B y using suitable plates in these jigs many odd shaped pieces can be drilled of which F ig 3 0 is a typical examp le The method of u sing thi s plate is shown by the illu stration B ushings A are placed in the p late B at the proper locat i on to guide the drills into the work The plate i s screwed on t op of t he vi se the stop C is adjusted to the p roper locat i on and the work D placed in the vi se agains t the s top after whi ch the holes are drilled This jig con struction adapted to drillin g holes on an angle In thi s case a swive l vi se is fitted i s illustrated in F ig 3 with a p late A set at the prop er angle in relat ion to the ba s e B Then by swing in g the vi se up to the p rop er angle the part s may b e drilled in duplicate as in the previous case ci ted That there are infin ite p o ssib il it i e s in the fitt ing of vi ses wi th bu sh ing plates when these are intelligently used wil l be readi ly seen by con siderin g the methods of drilling il lustrated in F ig 3 2 This i llu strates a swivel vise used as an index ing jig and where extreme speed or accuracy is not requ ir ed it works out very satis factorily The fir s t drilli n g i s done w ith the vi s e in the po sit i on illustrated The subsequent drillin g i s accompli shed by tilt in g the S wivel vise to the right an d left the de sired number of degrees A noth e r exam p le of dri ll ing in a vi s e i s shown in F ig 3 3 a number of holes be ing drilled around a circl e The work i s gripped between the jaw s in the vi s e proper a n d a bushi ng plate is located by pins A and B in the vi se B y sli d ing the vi s e to various posit i ons the hole s are dril led in the u sual manner This bushin g plate is removable for taki ng out the work The vi ses here illustrated are not always the most economical means Of handl ing work but they are often the be s t that the extent of the j ob will warrant They mu s t not be confused with more elaborate j i gs and fixture s which although vi s es .

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I G J

1 90

in pri ncip le are sp eci al in construct i on N ot al l shop s can a ff ord the costly design that the manufacture of guns or auto mobile s will warrant They must comp rom i s e on the cheaper and le s s effective equipment that can be adap ted qui ckl y to a wide ran ge of work and the machi ne Vi se as S hown in the foregoing can be made a universal fixture w ithin i ts l im it s The drill ing of M ultiple D rilli ng Jig of R e ve r s ib l e Typ e the spok e holes in the hubs of motorcycl es i s illustrated in F ig 3 4 .

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Fi g 3 3 .

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Vi p se

wi t h R m

rovi d e d

e

H

l

l

ovab e

o e s on a

Bu hing P l at e

C i cl r

s

for

D illi r

.

ng

e

These hubs are made of low carbon ste el and the end flanges through which the hol e s are drilled are 3 inch thick Through e ach fla n g e S ixteen N O 5 holes are drilled at a slight angle s o that the directio n of the drilli ng i s a l ong the l in es of a cone The di stance b e tween the h ole s is about one half inch The spin dl es of the multiple spindle drillin g machi ne in whi ch th e work i s done are guided in their inclin ation by a stee l ring support ed from the head of the machi ne The j g i s of the swi veling type permitting the hole s in one end of t h e hub to be drilled after whi ch the work hold in g part of .

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DRI LL

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1 91

D ill J ig f M t cycl Hub the j i g i s swi ve l ed 8 0 d e gr ee s a n d t he hol e s in the o pp os ite en d are drill ed T he dr ill in g i s p e rform e d by running the h e ad and dril ls down t o the work whi ch o n accou nt of th e in clin a tion of the spindl e s i s the o n ly way poss i b l e F i g 34 .

l

S wi ve ing

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1 92

D E S I GN

In order that the work may be quickly in s erted and removed the j g is made in halve s A s the illu s tration shows these halve s are hi nged at the left and held together for the drilling by a latch that appears at the right of the illustration The drill bushings are located in the faces of the halve s of the jig A fter the hole s in one flange of the hub hav e been drilled the steel plate that takes the thru t i s remov ed from beneath

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D illi g H l i P w P D i l P l t the work Then by withdrawing the index pin at the left the worki ng part of the jig can be turn e d 8 0 degrees to p re sent the other face of the hub to the dri lls The heavy stud on which the jig swi vels is directly behind the work and there fore not vi ible in the illu stration The index p in is inserted the thrust plate is replaced and the drilling of the hub is com l t s 6 The hubs each hav i ng hole in each end e e d p 3 are drilled at the rate of 3 per ten hour day F ig 3 5 .

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D E S I GN

on the table of a drill p ress and th e center p un ch was s et in the chuck in the drill spindle so that the prick—pun ch mark on the dial could be lined up wi th the spindle The plate was then s trapped to the t able and stud C dr i ven i n t o the center hole The top of the s tud C i s mach ined to fi t the pi vot hole in the arm D of the j i g The next step con si sted of l inin g u p the bu shin g A of t he fixture wi th the center pun ch in the dr ill spindle It wi ll be noted that the bu shing i s made adju s table relat ive to the center C about whi ch the arm s win gs so that i t may be se t i n the required posi t i on before clamping the b indin g bolt Th e bu sh ing is locat ed i n the proper relat i on to the notches in the di al plate by mean s of the lockin g pawl E and the eccentric s crew F adjust s th e positi on of the p awl relat ive to the arm D of the jig Th e p awl i s held i n the proper notch i n the d i al by the spring G which i s moun ted on the pins H and I and stud J is u s ed to hold the arm of the fix ture true wi th the fac e of the di al plate It will be e vi dent that after thi s setting has been made the bu s hi n g A i s located directly o v er the center punch mark whi ch was mad e on the dial plate whil e the pri ck punch was mounted in the punch block of the power press The hole ca n now be drilled i n the dial p lat e after whi ch succe ssive holes are drilled by simply swin ging the dial around the piv ot C and locking it for drilling each hole by dropping the pawl E into succes sive notches in the dial plate D u pl e x C lamping Ar r ang e m ent on D rill Jig The j g shown in F ig 3 6 is u ed for drilling and tapping s tud A which is made from by i inch cold drawn steel The end of the s tud enters h ole B in the locat ing block and thi s hole i s mi lled to provide clearance for the head of the s tud The work rest s on the drill bu hing which is sli ghtly counterbored to provi de clear ance for the tap The most intere s ting feature of the jig is that the cover and clamp ing mechani sm are both s ecured by the same knob ; clamp C holds the stud s ecurely in place when the knob is s crewed down and the same operation tighten s the co ver It will be readily s een that thi s principle could be employed on jigs and fix ture s u s ed for holding a great variety of part .

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CH AP T E R V III B O R IN G

I J GS

oring j i gs are g ene rally us e d for machi n in g ho l es where accuracy of alignmen t and Siz e ar e p art icularly essent i al and al s o for holes of large S izes where dri lli ng woul d be ou t of the que s tion Two or more ho l es in the same li n e ar e also as a rule fin i sh e d wi th t he a i d of bori n g j i gs Th e boring o p erat i o n i s pe rformed by bori ng bars havin g i ns e rt e d cu tte rs of vari ous ki nds and bori ng j i gs ar e almost always used in connection wi th thi s ki nd of borin g too l although bori n g o p erat i o n s may be sat i sfactori ly accompl ished wi th thre e or four lip ped drills and reamers The reamers may b e made so li d althou gh most frequently shell reamers mount e d o n a bar and gu i ded by bu sh i ng s are used The majori ty of holes p roduced in bor in g jigs whether dri lled or bor e d ou t are r e qu ir e d to be of such accuracy that they are ream e d ou t in th e last o pe rat i on The boring bars are usually gui ded by two bushi ngs one on each si de of the bored hole and l ocat e d as cl ose as p ossible to each end o f t h e hol e be ing bored The bar i s rotated and s imultan e ously fed through t h e work or the w ork wi th i ts j i g i s fed over the rotat ing bar : B oring j i gs may b e used e i ther in re gu la r boring lath e s in horiz o nta l borin g a n d dri l ling machi nes or i n radi a l dri lls The jig body is made e ither in o ne sol id p ie c e or com p osed of several members the sam e as in drill jigs The stra in on boring jigs i s usually heavy whi ch ne ce ssi ta te s a very ri gi dly de signed body wi th ribb e d and braced walls a n d members so as to allow the least pos s ible spring As bor ing j i gs wh e n i n operat i o n must be securely fastened to the machin e table means must also be provided in convenient and acce s sibl e p lace s for clamp ing the jig wi thout appreci ably spri ng ing i t B

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1 95

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6 9

JI G

D E S I GN

The p laces in th e j i g wh e re the bu shi ngs are located should b e provi ded wi th p lenty of metal so as to give the bu shings a S maller jig s sh o uld be s ubstant i a l b e arin g i n th e j i g body provid e d with a ton gue or lip o n th e surfac e whi ch i s clamped to the machin e table ; thi s permi ts th e o pe rator to quickly locate th e ji g in t h e ri gh t position As an a l t e rnat ive fin i shed lugs locatin g a gainst a p arallel or squar e may b e p rovided It is frequently advan tageou s to have small Size d bori ng jigs provi ded with feet S O that they can be used on a regular drill .

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F ig 1 .

u

G e n e ral O t li n e

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of

Si

m pl B e

ori ng

J ig

pre ss table in ca s e s where hole s to be bored out are to be o p ened up wi th a drill pierc ing the s olid m e tal It i s bo th e as ie r and Cheaper to do thi s rough drillin g in a drill p ress The gu ide bu shi ngs o f the same typ e as th e bushi ngs for drill jigs are made e i ther of cast iron or stee l and groun d to fit the boring bar which is also ground The bushin g s should be made rather long to in sure good b e ari ng The most common type o f B oring Jig o f S impl e D e s i gn boring jig for small and medium S ize work i s s hown i n F ig In thi s engravi ng A repre s ent s the work which i s held down by straps or clamps In many in stance s when the work is .

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D E S I GN

I G J

which case t h e fini sh e d bosses of cours e must stand in a ce r tain relation to the loca t ing poin t ; such boss e s are indi cated at E from whi ch measurements B can be taken to surfaces G on the work Th e thre e lugs H are p rovi ded for clamp in g pur pos e s the jig being clampe d in three p lace s onl y to avo i d unne ce s sary spr ingin g action If the jig i s in constant use i t would be advisab l e to ha ve sp ecial clamping arran gem ents as comp onent parts of t h e j ig for clamping it to the table ther e by avo i din g loss of time in fin ding suitable clamps The walls or standards K of large j i gs of thi s type ar e fre quently made i n loose p iec e s and secured and doweled in p lace In such a cas e the most important thi ng i s to fasten these ,

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F ig 2 .

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S

impl D ign e

es

of

Adju

l

s t ab e

B

oring

J ig

memb e rs firmly to th e base preventing shift ing by t on gues keys or dowels It is evi dent that when the standards are made loose i t i s e asi er t o fini sh the pad of th e base and t hi s i s of importance part i cularly when diffi cu l t locat in g arrange ’ ments are p laned or m illed in the base ; t h e patternmaker s ’ an d the molder s work is also simpl ified A s a rule the standards are screwed t o the bas e p ermanently and then the bu shi ng holes are bor e d In some ca s es however i t may be easi er to first bore th e h ol e in a l o os e p art an d th en a tt ach i t to th e main body Ad j u s table B o ring Jig s When bori n g j i gs ar e desi gn ed for machine p art s o f a S imilar design but of differen t dim ensi ons arran g ements ar e oft en made to ma k e one j ig take vari ou s size s In such a case one or both s tandards may have to be move d an d ext ra pads are provided o n th e fac e Thi s shi ft ing ,

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B O RI NG

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1

99

of the standards wil l take care of di fferen t l en gths of work S hould th e work di ff er in height a blocking pi ece may be made S ometimes sp ec i al loose brackets may be more sui table for replacing the regul ar sta n dards for S horter work If there i s a long di stance between two bearings of the work a thi rd standard may be placed in between the two out s i de ones i f the de sign of the bored work permit s ; thi s may th e n be u s ed for shorter work together with one of the e nd standard s In F ig 2 is H ere the jig con s i s ts of two S hown an adju s table bor ing jig part s A mounted on a common baseplate or large table pro The work B is located between the standard s vi d e d with T slots A numb e r of di fferent s tandard s su i table for d i fferent pieces of .

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F ig 3 .

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J ig

l c

o at e

d

o n and s

upp

ort e

d by th

e

W or k

work may be u s ed on the s ame ba s eplate The jig s or stand ard s are held down on the ba s eplate by Screws or bolt s and gen e ally located by a ton gue enterin g the upper p art of the T s lot s B oring Jig s u ppor t e d o n W or k B orin g jigs are frequently made whi ch are located and supported on the work F ig 3 shows such a j i g The work A whi ch in thi s case rep resent s some kind of a machi n e bed has two holes bored through the walls B and C Thi s j i g may gu i de the bar p ro p erly i f there be but one gu i de bu shi ng at E but i t is bett e r if i t ca n b e ar ranged to carry down the j ig member D as indi cated to give support for the bar n e ar t h e wal l B It may somet imes be more conveni ent to have two separa t e j igs located from the same surfaces on the top or si des In other ca s es i t may be better to have the members D and E s crewed in place instead .

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D E S I GN

of being solid wi th F and in some cas e s adjustabl e Of course these vari ations in de sign dep end up on the conditions involved but the p rinciples remain the sam e The ji g or jigs ar e held to the machine on whi ch they ar e used by clamping arrange ment s of sui table type Jig s for S upporting B ar on O ne S i d e of H ol e O nly The type of boring jigs previously described supp orts the bar in two or more p laces and the cutting tools are placed at certain predeterm i ned di s tance s from the e nd s of the bars depending upon the shape and size of the work S omet ime s it may prove n ecessary however to have a cutting tool i nserted just at the end of the bar F or example a boring jig may consi s t of .

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F ig 4 .

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m pl

E xa

e s of

Gu

idi

ng

O ne

m nt wh Hl t b

Arran ge S e of

id

s

e

o e

o

e

e r e no

b or e

d

S

uppo t i r

l

s ob t ai nab e on

imply one bracket as shown at the left in F ig 4 A v e ry lon g beari ng A i s then provi ded s o as to gui d e the bar tru e Th e arrangement shown at the ri ght in F ig 4 is som etimes used to in sure a long bearing for the bar A sp ecial bracket E i s moun t e d on the jig and bored out at th e sam e t ime as the jig p rop er i s machi ned Thi s p rovi des in effect two b e ar ings In these ca s e s bars wi th a cutti ng t ool at the end are u s e d There are everal r e a s ons why a boring j ig of thi s kind may b e required F or i nstance there i s a wa ll B im mediately back of th e wall C in whi ch th e hole i s to b e bored O ther obstacle s may be in the way to p revent p lacing a bearin g on o n e si de of the hol e to be finished In stead of havin g a sp ac e D betwe en the j ig an d the work the jig can oftentime s b e brought up Cl os e to th e work and clamped to it from the bu shing si d e E ach of the diff er e nt holes i n boring jig s has o f course i t s own outfit of boring -bars reamers and facing tools I n mak ing s

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2o 2

D E S I GN

may not be n ecessary wh e n uni ve rsa l jo ints are us e d between the spindle and the bar Jigs for M ultipl e B oring A s a rule but one hole is bored out at a time owin g to the fact that machi n e s for boring generally hav e bu t one sp indle S everal holes however could be bored out in a large size multiple spindle drill in whi ch ca se the jigs naturally ought to be de signed somewhat s tronger Another method of des i gn in g j i gs for boring two or more holes .

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F ig 7 .

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J i g for

B

ori ng

H ol

es

t

h ugh W k b ro

or

ot h

f m Sid ro

e s and

End s

a t the s ame t ime i s illustrated in F ig 6 the outlines only b eing shown in thi s illustration The gear box A contains the main driving gear whi ch is mounted on a shaft B which in turn is driven by the sp indle of the machi ne The gear on shaft B drives the gears and shaft s connected with the boring bars pas sing through the bushi ngs C D E F G and H The gears are proportioned according to the speed required for each bar whi ch in turn i s determ ined by the sizes of the holes The housing or gear-box A slide s on a do vetail s lide K A p art i cu la ly good fit should b e provi ded and the gear-box c an be fed along in relati on to the work either by table or spindle feed If .

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boring operat i on s are to be p e rformed in two direct i ons a J l g on the l ines indicated in F ig 7 is designe d Thi s jig may be mo unted on a special revolving table perm i tt ing the work and the j i g to be turned and indexed s o as to s ave r e sett ing and readjusting th e work a n d j ig when once plac e d in p os i tion on the machi ne The foregoing outl ine of boring j i g s i l lus t ra te s onl y t he funda mental principles i nvolve d it bein g co n s id e red more im p ortant to stat e the fundame ntal p rin cip l es in thi s co nn ecti on than to describe comp l i cated d e signs of tools i n whi ch the ap pli cati o n of such p rinciples may be m o re or less obscure or hidden ,

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F ig 8 .

mp l

E xa

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mall B ri ng J ig wit h R m ov b l H l di ng G ui d Bu hings

e of

S

o

e

o

a

e

,

e

L

e af

for

s

or ing Jig D e sign s I n F ig 8 are shown two vi ews of a small jig supported d i r e ct l y o n the work to be bored Thi s Jl g i s us e d for bori ng out a cross sl i de carr i a g e and is located on the work b y the dove ta i l sl i de a n d h e ld in p lac e by the two set screws A The two bushi n gs B ar e d riven into t he solid part of the jig a n d the two corre sp on di n g bushi ngs C ar e p laced in the loo s e leaf D whi ch is r emoved when the jig i s p laced in position on or removed from th e work The two set screws A do not bear di rectly o n the s i de of the carri age but are p rovided wi th brass or steel shoe s The leaf D ca nn ot be attached p erma ne nt ly to the jig and s imply s wung out of the way when the i s located on the work becau s e i t could n ot be swung i n fig place after the j g is applie d on accoun t of the small clearance —

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2 04

D E S I GN

in the cross sli de carri ag e The leaf is therefore made loo s e which i s an objectionable feature but lugs hav e been carried up on the casting o n both s ides of the leaf as shown to giv e good support ; these lugs are carefully fini shed to fit the leaf and the latter i s located and held in place b y ground p lugs In F ig 9 i s shown a borin g ji g which receives th e work A between two up rights The work in thi s ca s e is the tailstock of a lathe where two holes B and C are to be bored out The bottom surfac e of th e tailstock i s fini shed before borin g and i s located on the fin i shed bottom of the jig by m e ans of a k e y -

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F ig 9 .

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Co

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on

yp

T

e of

M

e di

um- i z s

e

B

ori ng

J ig

and keyway The keyway is cut in the J g and is a li ttle wi der than the key in the work and the s e t screws D brin g the key against on e si de o f the keyway that si de being in accurate relation to th e hol e B to be bor e d in the tailstock Longi — l the work i s l ocated b y a sto p pin aga inst whi ch i t i s t udi nal y brought up by a set screw from the opp osi te s i de The tail s tock i s he l d t o the j ig b y bo l ts E exactly as i t i s h e ld on the lathe bed The placin g of the set screws D at di fferent hei ghts i s one of the feature s of the jig ; this make s i t po ssible for the jig to take tailstocks of vari ous heights for different sizes of lathes raising blocks be in g used for the smaller sizes The rai s ing l

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D E S I GN

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to be bor e d and i t involves more or le s s work to get the J g in order The jig in F ig doe s not need to be as heavy as would be inferred from the illu stration becau s e a large portion of the bottom can be cored out The bor ing j g i llustrat e d i n F ig F our -par t B oring Jig con sis ts of four p arts ; the up right members A B and C and the baseplate D whi ch l atter may b e used for all jig s of similar construction Thi s typ e of borin g j ig i s used only for ve ry large work In th e cas e il lustrated larg e l ath e heads are to b e bored The work i s located on the baseplate between the two m e mbers The member B is only used when the di s tanc e b e A and C l

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F i g 11 .

B

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i i U p i ght c yi

ori ng

J ig r

c

ons s t ng o f s

arr

ng

B

p l t nd S p G ui d B u hi ng

as e

th e

a e a e

e

s

ar at e

Re

movab l e

s

tween A and C i s very long so that an auxiliary s upport for the boring bar is required or when s ome ob s tacle prevent s the bar from p ass ing through the work from one of the out side members to t h e ot h e r AS a rule these members are located on the basep late by a t on gue fitt ing into one of the S lots as S hown a t E The members are brought as close as po ssible to the work su ffici ent spac e of course being permitted for the cutting tools to be in s ert ed The s tandard s are cored out and ribbed and lugs provided so as to giv e the bearing bu shings long and sub s tantial s upport G ood re ult s will be obtained ,

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B O RI NG J I GS

207

wi th

this type of j i gs provi ded they are carefully set up on the baseplate A t F in the member B i S hown a bo s s ; thi s i s pro vided with a tapped hol e for a hook or eye bolt to facili tate moving th e j g member by an overhead crane The other members have tapp ed hol e on th e t op for the same p urp ose 2 Align me nt of Jig wh en H ol e s ar e at an Angl e I n F ig i s S hown a bori ng j i g for bor i n g out th e to p fram e A f or a di al drills Th e design of th e jig i s S imp le but e ffectiv e ; the hole s

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F i g 12 .

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J i g h avi ng

W e d ge -s h ap e d at an

Lc

o ati ng

Angl

Pie

c

e

for

B ing H or

l

o es

e

i s p aral le l w ith the fini shed S i de C of t he j i g and i s bored out after the ji g has been brought up squar e aga ins t a parallel and strappe d to the machi n e t ab l e The hole D i s bored at an angle w i th the hole B and t h e s et t ing of the j ig for the boring out o f thi s h ol e i s fac il ita t ed by provi din g a wedge shap ed p i ece E of such a n an g le that the jig wi ll be s et i n the p ro p er p o si t i on wh en move d up again s t the wedg e If universal jo ints are used f or connect ing the boring bar wit h the driving spindl e the s e tt ing of the work a t an angle could be omitted although i t i s p referable even when us ing un ive rsal joint s t o have the boring -bars as nearly as p o ssible in line with the S pindle This elim inate s a great deal of the eccentric stress e specially when taking a heavy cut with coarse feed B

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I G J

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B orin g o p erations are Us ing Work t o G ui d e B oring-b ar s omet imes carried out u s ing p art s of the machine itself as g uid ing means for the boring bars and in s ome instances it is very e ss ential that boring operation s be p erformed in this way i n order to obtain perfect alignment In F ig 3 i s S hown a ma chi ne bed with the headstock soli d wi th the bed In th e top view is shown a method for boring out a hole at B b y the use ’ of two j igs C and D whi ch are located on the V s of the machi ne and held down by hook bolts If the hole B only passes through the part E of the head this would be the p referabl e way of .

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F i g 13 .

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m pl

Exa

e

i ll

u

s tr at ing

Use

W or k

of

as a

ud

G i

e

for t h e

B

oringb ar

boring i t In some instance s however the hole B may be requ ir e d to be in ali gnm ent wi th the holes in a carriage or in a bracket as at F and G These hol e s of cours e can th en b e u s ed t o great advanta ge as guid in g means S hould the ho le s be too large to fit the boring bar cas t i ron bushi ngs can b e mad e to fit the hol e s and the bar The front el evat i on in F ig 3 shows how a cross sl ide carri age and ap ron I whi ch h as a hole J i n l ine wi th the holes in bearings K L and M and travels between K and L can be bored out by using the brackets K L an d M to guide the boring bar B y k e ying the trave lin g .

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D E S I GN

locat in g th e work in a sep arate drill j i g I n oth e r case s i t may be better to do the drillin g first and l ocat e the work for the borin g operations from the drill e d holes The designer should decide whi ch method would be preferable con sid ering the time requi red and the accuracy of th e work It is impossible to gi ve any defini te rules for this work ; but i t may be s ai d that com binat ion jigs S hould be used only when the drilled and bored hole s have nearly the same di ameters As a general rule when the hole s are of wi dely different di ameters two jigs are pref e r able F or examp le if a few holes of small diameter for holding a collar or bracket w e re located around a large bored hole and were drilled wi th the same jig used for the large hole the jig when used on a small drill pre s s would be entirely too heavy to manip ulate It is likely that in such a ca s e a small separate drill j ig could be attached d irectly to the work In many other ca s es however it will prove a di s tinct s aving to combine the boring and drilli ng jig in one In F i gs 4 and 5 i s S hown a comb inatio n drill and boring i of large S ize The work con s i s t s of a headstock for a lathe j g with a number of holes to be drilled The large hole B F ig 5 at both ends of the head s tock are cored as usual and allow the boring bar to enter for takin g the roughing cut The holes at C and D are open e d up by dr ills p revi ou s to the boring opera tion AS there i s considerable di stance between the end of the headstock and the uprights of the jig long bushings are u s ed to give the tool s a good bearing close to the work B oth the drilling and boring operations may b e p erformed o n a hori nt a l boring and drilling mac hi n e A s the horizontal boring and drilling machine s usually have adju stment i n all di e c tion s the only moving of the j g nece ary i s to turn it around for drilling the hole s on the oppo site side s .

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CH A P T E R I X

M ILLIN G

X

AN D P LAN IN G F I TURE S

M illin g

machin es ar e n ow used for s o many diff erent p urp oses that the fixtures us e d for holding p arts to be milled diff er con s i d e r ab ly in form and s ize and there are several dist i nct types The simp les t form of mi lling fixture i s r epresented by the type whi ch s imp ly hol ds and l ocates a s in gle pi ece for a milling op erat i on Then there are mult ip le or gan g fix tures for hold i ng a row of dup licate cast i ngs or for gings Thi s type may be intended either for machines having a strai ght line feed ing movemen t or a circular mot ion as in the case of mach ines “ O ther mi l ling fix tures de signed for continuous m illing which often are more complicated i n de sign than the work holding fixtures are arranged to hold the work in different p osit i ons e i ther for milling su rfaces whi ch are at an angle or for milling at vari ous po ints around a ci rcular p ar t The p ath followed by the mill ing cutter i s al s o controlled by som e fix tures e specially i n connect i on wi th profile mill ing ; or the fixture ay be con s tructed to gi v e th e work a rotary feed i ng mo v e ment a s when milling a curved slot or groov e o n a cyli ndri cal part S ome idea of the variation in diff e rent types may be obtained from the de sign s illustrated i n thi s chapter il lin g and other fix t ur e s in C are S hould be taken to des i gn m such a way tha t the p ar t s to be machin ed will be p rop erly located and so tha t th e o pera t or who us e s the tools cann ot get t h e work in wron g and thu s sp oil th e p arts The fix ture should b e e a sily loaded and un load e d a n d i t S hould b e as o p en a s poss i ble to make cl eanin g easy a n d to p revent p ock e ts for chi p s H ardened st e el sea t s should be ground p aralle l wi th the base after ass embl ing to obtain the be s t results T 0 brin g the cost as low as po s sible the tool parts should be standardized wherever practi cable The bodies and ba s e s of fixture s S hould .

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212

be made of cas t i ro n a n d kept in stock in various s iz e s to m eet the requi rements of the sho p whene ver thi s i s p racti cabl e C lamping cams dowel p i ns bolts and screws S hould be mad e up in large quantity and steel s eat blocks s traps a n d other steel parts should be made of standard stock siz es i f p ossibl e to pr e vent unne cessary machi ni ng .

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F ig 1 .

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Jaws for Vi s e The ch e ap est k in d o f mil li ng fixture that can be bu ilt i s a p ai r of d e tachable vi se jaws as S hown i n F ig Th e se jaws are mad e of cold rolled st ee l a nd casehardened They can be r emoved from the vi se qui ckl y an d rep laced by other jaws It i s advi sabl e howeve r to us e vi se jaws onl y where gr e at accuracy i s not r e quir e d such as —

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ixtur e for Angular Work O ccasi onally in every line of manufacture th ere are p arts whi ch are S im p le in appearance but di fficult to mach in e F ig 5 shows a p art of a belt shifter used on an automat i c machi ne the mak e rs of whi ch u se eight diff erent S hap ed p ieces of thi s kind Th e stock is flat and one-half inch thi ck If the S i des of the slots wer e perpendicular the manufactur e of the s e piec e s would be ve ry simple but the S id e s are not perpen di cular and the angle s they form with the bottom differ wi th each different shaped piece As a result these p i ece s are difii cult to manufactur e without th e p rop e r form of fixtur e Ad j us table

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The fixture shown in F igs 6 to 8 con si s t s of two parts A and B whi ch are clamp ed tog e ther when in the proper posi tion by bolts p a s s ing through holes in th e lower casting A and S lots i n the upper ca sting B A tongue planed in the bottom of the base A fit s a s lot in the m illing machi ne table to which the ba s e is bolted The upper part B is turned to fit the lower part so that no gib i s r e qui red The part s to be milled are held in place by a set scr ew whi ch is not S hown E ach sh ape h as i t s own number and thes e numbers are stamped upon the top surface of the ba s e A The upper part of the fix tu e can move in either direction from the cente s that by placing .

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F ig 5 .

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XTURE S

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P art s e d in F i gs 6 t o 8 , .

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P t h w i F ig 5 t h e l ocating pin C in the p ro pe r hole as shown by the number the fixture can be qui ckly set for machining any shape F ig 6 shows the diff e ren t S ize cutt e rs milling projectio n s D and E F ig 5 ; in F i g 7 the central S lot F F ig 5 i s being cut F ig 8 F ig 6 .

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D E S I GN

I G J

and pin F in th e ho l e 0 Thi s s e ts th e swive l p l at e A a t the requi r e d angl e and a l so l ocates th e cross S li de C a t the requi red di st ance off center to enable th e work to b e mil l e d by the ou t er e dg e o f th e cutter Aft e r thi s operat i on has b e e n com the sw i v el plate A i s swung o v er to enab l e the pin E t o d l t e e p enter the hole K S imilarly the cro ss S l i de C is moved so tha t the pin F w il l enter the hole M Thi s brings the work in po si

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tion to enabl e the angul ar side B to be mi lled by the outer edg e of the other cutter on th e arbor i L e ve r op er at e d F ixt ur e for M lling O il gr oove in B u s hing F igs and 2 S how a sp e cial m i llin g fix tur e d e signed to hold the brass bushing A wh ile mil ling the oil-groove B The fix tur e wi th the bushing in place may be se en in F ig The deta il ed constructi on of the fix ture however will b e more clearly .

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un d e rst oo d b y r eferr ing t o F ig 2 Th e fixtur e con s i sts of a base C whi ch carri es a s li d e D se t a t an a ngl e of about 3 0 — de gre e s wi th th e bas e Th e V b l ock E supp or t s the work whi ch i s he l d b etwee n th e a n gl e p la t es F a n d G P la te F forms a s t o p for th e w ork whil e p la te G is mi ll e d t o mak e p rovi si on f or the in ser ti o n o f th e we d g e H T h e ha n d l eve r J i s mor e clearl y s h own in F ig I I To o pe ra te t h i s fix t ur e whi ch may be used o n any m illing machi ne th e cu tte r K i s p l aced in th e horizo nt a l spin dl e of the machine a n d t h e fix t ur e s e t up facing i t Th e method o f ho l din g the bush ing durin g the machi n ing of the groove i s ap p are n t from the i llustrat i ons wh i ch S how i t s e ated in the V block and held firmly betw e en the a ngl e 1

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F i g 11 .

p l ates

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M illi ng O il -gr oove

b y th e wed ge Aft e r the wedge has b ee n dr i ven into place the cu tte r i s f ed in t o the work to t h e requ i red dep th and sli de D i s op era t ed by m e an s of h a n d-l e v e r J advan cing the bushing unti l t h e p r ope r l ength o f groove h as b een m ill ed Thi s fix ture cou l d n o doub t b e gr e a t l y imp roved up o n b y th e addi t i on o f bet te r m e ans of clampi n g t h e work a n d coul d also be mad e to han dl e a wi d e r range of work by the addi ti o n of sui tab l e s top s fo r c o n tro lling the l en gth o f th e cut H ow e ver for the p art i cular wo rk f or whi ch the fixtur e w as de si gned thi s w as n o t tho ugh t ne cessary as t h e qua ntity o f pi ec e s to be machined di d not w arra n t i t In d e xing M illing F ixt ur e for Roll e r S e par at or Th e bronz e roller sep arator s s een i n F ig 3 form part of the roller bear i ng of a gun moun t upo n which the carriage turns when tra in .

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2 20

D E S I GN

ing t he gun or adjustin g it horizontally Thes e sep ara t ors have twenty four hol e s and oppo si te holes must b e in a lignment and in a radial position as otherwise th e re wi ll be a creep ing acti on of the rollers relative to their bearing rin g s or tracks A m i l li ng mach in e equ ipp ed wi th a s im p le typ e of indexin g fix ture i s u s ed for thi s work The base A of the fixture i s bolted to the machin e table and the upper p art B i s free to revolve Thi s revol ving member has accurately spaced hol e s whi ch are engaged by indexing plunger C A fter the hole s have been .

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D t i l Vi w f M illi g F i t u h w i F ig 11 drilled and reamed they are counterbored by the u se of su i t able tool s The separator rin g s are located on the fixture by mean s of the central bore In d e xing F ixt ure for M illing C lut ch e s The de sign and con s truction of a special form of fixture used for cutting the clutche s on transmission drive p inion s and S liding gears i s s hown in F i i Th ture consi ts of a frame into which fi x A s 4 g the sp indle B is fitted The spindle i s de signed to s erve as a collet chuck on the upper end and is arranged to carry the large index plate C at its lower end The index plate h as a s eries of holes E dr illed in it at a con v eni ent angle to recei ve F i g 12 .

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222

fixture i t is customary to put a sheet metal washer between the lower face of the pinion and the top surface of the chuck ring I in order to keep chips and oil from runn ing down into the divi di ng head When milling the clutch gear J the sp l i t co ll et i s re p laced by t he expan sion chuck K The body of thi s chuck fit s into the spindle and is locked in posi tion by the chucking ring I The work is held on thi s chuck by expanding i t by mean s of the taper headed screw L which is turned by a square key -

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F i g 14 .

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Cros s -s e ti onal

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D t il f W The hard e ned ste e l collar M is fitted on the chuck to p ro vi de a good beari ng s urfac e and re si st wear Th e clu t ch gear is shown in position on the chuck by dotted lin e s E ight cuts are required to com p l et e the m i ll in g o pe rat i ons on one of these clutch gears and con s equently i t i s neces s ary to us e an eight point index p late A fter sett in g to bring the cutter to the requi r e d depth th e mi l lin g machi ne saddle is move d in un til one e dge of th e cut te r regi sters wi th a p oint inch to the left of the c e nt e r ; fo ur cuts are then made complet ing o n e S ide of the clutch tee th To m ill th e other side of the teeth th e milli ng machin e saddle i s move d out until th e other side of the cutter re gis t ers wi th a point inch e a

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MI LL I NG

FI

X TURE S

2 23

t o the ri ght of the cent e r The head is th e n ind exed i re volu t i on to m i ll t h e S ide of the fir s t tooth and the n i revolution for takin g each of the three rema ining cu t s Th e clu t ch t e eth a r e cut a li ttle off cent e r i n ord e r t o gi v e th e c l u t c he s th e r e quire d amount of clearanc e The i deas embodi ed in th e design o f thi s spe cia l fix t ur e may sugge s t oth e r us e s for a t oo l of thi s kin d wher e it i s r e qu ired to p erform millin g dril ling a n d oth e r o pe rati ons o n work for whi ch the regular mi llin g mach in e di vi din g h e ad i s not sui table .

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F i g 15 .

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u ou s M illing F ixt ur C nn ct ing- d

Contin

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Lib t y M er

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Milling F ixtur e F ig I 5 shows a cont in uous mill in g fix t ur e whi ch i s emp l oyed f or the mil l ing of connecting rods o n a doub l e spindl e ve rtica l mi lling machi n e F our sur faces ou the rods are m il l e d at once the top and bottom surfaces at each en d bein g m ill e d simultaneously The main spindle whi ch i s p ro vi ded wi th t wo cutters one for the upper and on e for the l ower surf ace m ills the outer end of the rod whi le the auxi liary spindl e wit h cutters mounted in a S imilar manner mill s the ins id e end of th e rods F ourtee n connecting-rod s ar e m oun te d in th e fixtur e a t a tim e a n d as th e fixture rota te s o n th e tabl e th e fini sh e d rods ar e t ak en ou t and n ew rods ar e i nsert e d b y the op erator whi l e the work progr e sses E very Co nti nuou s

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other jaw for holding the connecting rods is fixed while e very a l ternate jaw is pivoted at one end B y clamping against one -

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2 24

D E S I GN

rod with a clamping screw at th e extreme end of the pivo te d clamp pre s sure is brough t to b e ar upon the ends of th e c on i rods o n e ach i d e of the pi vot e d clamp thus mak ng S ne c t in g the clamping v e ry rapi d A t the in side end one cl am p a l so holds two rods in p lace This clamp is provided wi th a sma ll pin which fits into a slot in the clamping stud so tha t wh en tightened th e clamp must always be in one po sition and cann ot com e out far enough to interfere with the milling cut t ers ,

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F i g 16 .

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F

i

xt ur e

u

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for Ro gh - ini ng

a

Cir

cul ar S l ot in S ight -b ar

R adial fixture s are so called ial Milling F ixt ure s becau s e they are u s ed for machining parts to a gi v en radiu s In general the work holding part of the fixture is eithe pivoted or i s guided by a curved track so that i t i s given a circular mo tion when i n us e S ome ingeni ou s ra di al fixture s u s ed for machi ni ng the S ight bars o f naval gun moun ts at the plant of the M ead M orri s on M fg C o E ast B o s ton M as s will be de s cribed The radial or circular surface of the sight bar mu s t be so nearly perfect that the sight may be operated through its complete range of adju s tment s without any binding action and without perceptible lo t motion between the mo ving part s Th e curved surface s of the sight —bar and of the bearing in the sight bar bracket mu s t be exactly concentric with the axi s Rad

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th e same radi us as the S lot B in th e fix t ur e A we ight i s at t ach e d to the sad dl e of the machi ne by means of a wi r e cabl e which is con ne cted at D The obj e ct of u sing a weight i s to hold block C in contact wi th the slot on one side and thus by eliminating all p lay it is po ssible to secure a higher degre e of accuracy A two lipped end mi ll is used for thi s operat i on The slot is mi lled in ch wide a n d 3 inch deep An other ra di al fix t ure of th e gen era l t ype just d e scri b e d i s .

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D iff t O p ti S ight -b shown in F ig 7 Thi s fixture i s for the bronze bracket through which the S ight bar slides whe n be ing elevated or lowered It h as a curved slot which must b e mi lled to the same radiu s as the sight bar to avoid any cramp in g or b inding action A fini shed s urface on the bracket A is clamp ed again s t a top plate or bridge B of th e fixture and it i s further located by a plug C at the right The ba s e of the fixture fits between curved track s or gui ding strips D A t one end of the fixture a tran sv ers e slot is formed and thi s i s engaged by a block pivoted t o a nut through whi ch the feed screw pa ss e s The feed s crew i s con ne c t e d by gearing E with the regular feed rod of the machine F i g 18 .

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MI LL I NG

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FI

XTU RE S

22

7

and as t h e ovabl e secti o n of th e fixtur e i s f e d along a slot is milled to the s ame radius as the tracks T he curved si des of th e P ivot e d Typ e of Ra d ial F ixtur e S i ght bar and also the b e veled surface s along one edge ar e milled by mean s of a radial fixture of the typ e shown in F ig 8 Thi s g eneral s tyle of fixture is u s e d extensi vely in connection wi th oth e r o p erations on the si ghting mechan i sm It has a very heavy base casting A wh i ch is bolted to the tabl e of th e ma ch ine Th e sight bar B i s held on the sw inging part C of the fix ture whi ch i s p ivot e d at D At th e work holding end of t he swmgi ng member there is a swi vel ing nut through which p asses a f e ed screw Thi s feed screw i s connected by gearing l oca te d a t th e en d of the table wi th the regular feed screw of the machi n e th e nut in the m illing mach ine havin g been re move d ; consequently , whe n a sight bar is be ing milled the p art C of t he fixture i s gi ven a circular mo vement about the pivot D as t he p ower f eed trav e rses i t from one end of its swing to the oth e r Th e i llustrati on shows the machin e m illing the beve l e d ed g es on the top o f t he S igh t bar Wh e n the S ides are bein g m ill e d the cutter S hown at E is us e d A fter o n e s ide h as be e n milled the stops F are transf e rred to the opposite side so t hat th e y wi ll not in t e rfer e with the cutter The gage u s ed for t e st ing th e radius of the inner surface forms part of the fixtur e and consi sts of a bar G whi ch is free to S lide through a block H Th is block i s also free to turn about the sam e p ivot which i s us e d for th e swingin g p art of the fixture The radi us of the sight bar i s t e sted by bringing the g ag e p o int into con tact w i th i t and the n not ing th e p ositi o n of the end of bar G relat ive to the outer surface of b l ock H When the e nd of the bar and the surfac e of the block are exactly in the sam e plane as indicat e d by tests made wi th a d i al gage the work i s correct The S ight-bar i s located in th e fix ture b y th e fini shed face of the head which also s e rve s as a common locat ing point for many other operat i ons Th e re is considerable o v erha n g of the fixtur e relative to the machi ne table and i n order to avoid sag the overhangin g part is counterbalanced by a heavy weight attached to one end of the wi re cable J which p asses over p ulleys fastened to the ceiling ,

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D E S I GN

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MI LLI NG

FI

XTURE S

23 1

with thi s fixtur e the attach e d cables E an d F p ass in g ove r pul leys abo ve Thes e weights not only counterbalance the ove rhanging parts of th e h e avy fixture but also make it easier to el evate t he kne e for fee di ng th e cutter down past t h e work n i ix r h ving H a d a n d P ow r F u e a e Ope r at e d F e e d t Rad al Th e yoke of the sight mechani sm is a cast steel member which c arr ie s the telescopes at i ts forward e nd and is attac h ed at the ,

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Li rear to the sight-bar There are some ra di al m illin g operati ons on the rear end of th e yoke The cur ved surface s at the end of the yoke are m ill e d to the requi red radius by a typ e of fix ture whi ch in many respects is s imil ar to the radial desi gns already referred to in connect i o n wi th th e si ght bar Th e base of the fixture !se e F ig 2 ) is bolted to the t able of a column and knee typ e of mi l lin g machi ne and the upper part B is free to swing about a p ivot located at the requ i red ra di al di stance One radi al mill ing O peration is t h at of form -mi l ling the worm -gear segm en t in wh ch worm teeth ar e cut later to mesh wi th a worm whi ch enab les th e yok e to b e adjusted horizontally S evera l Fi g 21 .

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J IG

234

D E S I GN

again t the roller ; therefore when the mi ll ing machi ne table i s fed in a lengthwi s e direction the former and liner turn in uni on as the curved section of the openi ng is mil led Two lugs on the hub of the weight le ver alternately engage a s top and in as the le ver i s turned from one po s ition to the other this way either the lower or upper side s in the ma s ter former are held again st the roller C The liner h as a similar opening on the oppo site S ide which is milled by S imply connecting the upper end of link D wi th the oppo site end F of the double exten sion arm !se e end view F ig D u pl e x F ixt u re for Rou ti ng O il-gr oove s A duplex type of fixture u s ed for routing oil groov e s in bronze bu shi ngs is shown in F ig 2 3 The rout ing operation is performed on two bu shing s imultaneously and a drilling machi ne i s used for the operation The oil groove s of the bu shings in thi s par t i cu lar ca s e extend around about two thi rd s of the circum ference of the bu shing and branch out into a Y shape at each end The horizontal spindle of the fixture is rotated for feeding the bushing past the routing tool s by handwheel A which serves to revolve a worm me shin g wi th wheel B The axi al movement of the fix ture spindl e is derived from cam groove s on each side of gear B The S hafts C and D carryi ng the roll e rs have rack teeth whi ch engage the segment gears formed on the pivoted lev er E B y swinging this lever in o n e di rection or the other the rollers are altern ately engaged When th e left hand roller i s engaged with its cam gr oove the left ha nd branches of the Y S haped oil groo ve s on each bushing ar e milled and when the right hand roller is mo ved inward the ri ght hand bran che s of the o il groov e s are milled P l aning F ixt ur e s F ixture for plani n g are as e ss ential for interchangeable manufacturing as are drilling jigs or mill ing fixture s P laning fix ture s s erve primarily the purpo s e of locating and holdi ng the work but they are often provi ded with s etting pieces or templet s whi ch are u ed for s etting the cutting tools so that the work is always machined in a certain relation to th e locating means o n the fixture itself S ome mi lli ng fixtures al s o have thi s tool sett ing feature The strength of fixtures S hould be gov e rne d by the kind of s

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P LAN I NG

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XTU RE S

23

5

operat i o n to b e carrie d out o n th e w ork whi l e in t he fix ture whether p la ning m il ling slotting e t c a n d how much stock i s to b e r emo v e d A m ill in g fixtur e as a rul e mus t b e made strong e r tha n a p l ani ng fix tur e b e caus e a m illi ng cu tt er or M a n y of the d inarily t akes a h e avi er ou t than a p lani n g t oo l f e atur e s of te n found on mil l ing fix tures may b e app lie d to p l aner fix tures wi th whatever cha nge may b e ne c e ssary o n accou n t of the parti cular ope rati on r e qui r e d A s a rule mi ll ing and p lan ing fixtures are provi d e d wi th a t o ngu e o r k e y in th e base for locatin g them o n the ma chi ne tabl e S uit abl e lu g s sho u l d a l so be provided for clamping th e fixtur e t o th e p lat en The most commonly used fix ture for p l a ning S haping an d milling is th e vi se S tandard vi ses ar e indi sp e n sab l e in p l ane r or mil lin g machin e work or o n the shap er a n d by slight cha n g e s they can be us e d for a large vari ety of small e r pi ec e s Th e regular vi se jaws ar e often r ep l aced by fal s e jaws whi ch may be fitted wi th locating p in s a n d s e a t s a n d h e l d t o t h e vi s e t h e same as the re gul ar jaws Vi s e s wi th fa l s e vi s e jaws ar e e s i l ada p ted for m i l l i ng o pe rat i o n s but v i ses are n o t usually l e c a y p employ e d for long work sp ecial fixtur e s b eing commonly used P lan ing F ixtu r e s fo r Lath e Carr i ag e Cas ting A ssume t hat a s e t of planing fixtur e s for the p iece s hown in F ig 2 4 is re quired Th e work i s a S lide or carri age for a lath e The finish in g marks gi ven o n a n umb e r of th e surfac e s in di cate where th e work i s t o be fin i shed In t h e first p lace i t must b e con s i der e d from whi ch sid e s to l ocate and how to l ocat e and hold th e work without springin g it a n d in wha t ord e r th e o pe rat i ons should be p erformed to b e st advan tag e F ig 2 5 S hows a fixtur e for roughin g out th e w ays on th e bot t om Th e s lid e i s l ocat e d on three fixed l oca t ing p oint s A a n d the s l i d in g p o in t B Thi s lat t e r is adjustable in ord e r to en ab l e p l aning t h e s li d e as ne arly as p ossibl e to uni form thi ckne ss S ometim e s i f t h e p arts A F ig 2 4 b e vel toward the en ds lugs G may b e added ; t h e s e can th en b e fini shed a n d us e d for locatin g purpos e s Th e car riage as shown in F ig 2 i s furth e r located aga in st th e p in s C 5 in ord e r t o in sur e t ha t th e cross s li d e of t he carri ag e wil l b e squar e with th e bot t om ways The S l id e i s brough t up s i d e wi s e again s t t h e pin D an d th en cl ampe d do wn i n co n venient

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236

I J G

F i g 24 .

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L th a

F i g 25 .

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e

C arr

i

age

C as t

i ng

in P l an e r

F ixt

ur

e

D E S I GN

m pl

An E xa F xt r e

u hp

e of

i u D ign

for Ro g - l ani ng

W or k i ll u s tr at i ng

es

Way s

for Carri age Cast ing

Po

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nt s

23 8

JIG

D E S I GN

The fix ture for th e next o pe ration is S hown in F ig 2 6 Thi s fixtur e is made to receive th e carri age and locate it by the n ow rough-finish e d ways ; in t his fixture t h e cross slid e dove tail is plan e d Th e S lide rests on four fin ished p ads A an d th e s traight S i d e B o f th e w ays in th e sl i d e brou gh t u p a g a in s t t h e fin i sh e d .

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B tt m W y surfac e s C If no other part i s ava il able for clamping th e fixtur e on the machi ne t able lugs E ar e added If ther e ar e no ta per ing surfaces th e fixture can b e loca te d o n th e machin e tabl e by a ton gue or by placing a fini sh e d side again st a parallel Th e slid e or dove t ail is now rough e d out an d it i s usually suffi ci e nt ly accurate practice to fini s h it in t h e sam e s e tt in g e s F i g 27 .

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F ixt

ure

for F ini s

h-pl

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P LAN I NG

FI

XTUR E S

239

as S l ides mus t always be scrap e d and fit t ed t o suit the machi n e o n which th ey ar e to be us e d The nex t ope ra tio n woul d b e pe rform e d in th e fix tur e illus Th e ca rriag e i s h e r e l o cat e d b y t h e dovetail t ra t e d in F ig 2 7 an d by th e pin B an d he l d b y a gib C or by strap s a n d scr ews as S hown It will b e n ot i ced t hat with t h e gi ven d e sign th e s t rap s an d scr ews mus t be r emove d e ach t ime a n ew p ie c e is in sert e d whi ch i s a n u n d e s i rabl e fe atur e of t h e fixture If parts A in F ig 2 4 p roj e c t out t oo f ar so t hat a light fini sh in g cut would caus e sp rin ging t h e y are supp orted by S li ding po ints or other adjus t abl e l oca ting m e an s h a d I f t h e doveta il in th e S l id e S im pl y b een rough finish e d in t h e fix t ure in F ig 2 6 th e fini sh ing o f the b otto m ways could have b een do ne in th e fixture in F ig 2 7 a n d the n after h avin g fin ish e d t h e b otto m w ay s in thi s fixture the work could again have b een l ocat ed in t h e fix t ure in F ig 2 6 an d th e dovetail fin i sh e d ; thi s mi ght in sure mor e accura te work in some cas e s In t h e cas e jus t descri bed the work r e quire s three d iff e r en t fixt ur e s to b e compl e t e d The numb e r of fix tures to use i n each cas e i s en t ir ely d epen d ent upon t he n a ture of th e work Wh en t h e r e i s a l arg e amoun t o f work of th e sam e kin d to b e done s ev er al fix tures o f t h e sam e type ar e made up for th e sam e piece and wh en in us e t h e s e fixtur e s ar e p l ac e d in a row o n the tab l e of t h e machin e G ang-plani ng F ixt ur e s It i s very commo n in pl ane r p rac ti ce to loca te a n umb e r o f dupl i cate cast in gs or f or ging s in a row extending l engt hwi s e o f t h e t ab l e a n d then p l an e t h em all a t th e sam e tim e Gan g p l ani n g i s oft e n don e wit hou t a spe c ial fix ture by simp ly cl amp ing th e work d i rectly up on the t abl e bu t fix ture s mak e it po ssibl e to s e t up work mor e rapidly and accura tely B es id e s ma n y p iec e s ar e o f such a shap e t ha t a fixtur e i s ne c e ssary in order to hold t h em in t h e corr e ct p osit i on for planin g An examp l e of w ork r e qui ring a fix tur e i s S hown in F ig 2 8 Twenty three for gin gs ar e p l ane d at o ne t im e and four cu tting t ools ar e us e d two b ein g h el d in th e s id e h e ads whi le two are a t tached t o t h e h e ads of th e cross ra il The forg in g s are l o ca t e d at ri ght a ngl e s to th e l e ng t h of the p lane r tab l e i ally c e p

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2 40

J IG

D E S I GN

C H AP T ER X

AD J US TAB LE

X

F I TURE S F O R TURRET I VE RTI C B O RI N G S

M LL

AL

LATHE S

AND

When p i ec e s of th e sam e type but of vari ous s izes are to be mach ined on the turret lathe or verti cal boring mill it is somet imes de sirable to design t h e t ools and fixtur e s in such a way that they can be adap t e d t o handle the d iff e rent p i eces thus avo idin g the n e c e ssi ty of p rovi ding a s ep arate tool or fix ture for each pi ec e N aturally wh en th e p roduct i on i s la rg e such a p rocedure as thi s would b e unp rofitable becau s e th e t ools could only be used o n on e pi ece a t a t ime and a lot o f piec e s of one size m ight b e held up f or a consi derable tim e wai t ing for a lot of anoth e r S iz e to be mach ined When however the work comes along in lots of from I 00 to 2 00 pie ces a gr ea t saving in tool cost can be eff ect e d by the us e of adjustabl e tools and fixtures providing the de sign of the p arts is such tha t i t wil l perm i t of followin g thi s p racti c e Much depends upo n the shape of the work to be held and its machin ing requiremen ts There ar e in s tances wh en the desi red results may be obta in ed by simple means and there ar e other ca s es which requir e th e application of considerable ingenu it y in order to avoid com plication s in the de sign P roperly design e d an d car eful ly bu ilt tool s and fixtures of th e adju s table typ e ar e profitable invest ments on certain classes of work and the ir advi sability should ,

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be carefully con sidered when several pieces of the same general type are to be handl e d The great e s t forethought i s neces sary in de signing fixtures of thi s kind in order to make sure that e very point for e very piece h as rece iv ed proper con siderati on There is probably no other type of fixture whi ch requi res so much care in i t s design and for that reas on the important p oint s given herewi th should be mo s t carefully noted Important P oint s in D e s ign The number of pieces to be machin ed should be the firs t po in t consider e d as thi s natu rally has an eff e ct on th e d e sign of th e tools and fixtures .

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242

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AD J U STAB LE

FI

XTUR E S

243

The l arge st and small e st pie c e s in t h e group should be and the machi ne on which the work is to be done s e lect e d S hould be determ in ed accordi ng to the s iz e s of th e se p i eces If the variat i on in size i s con siderable it may be economical t o do a p art of the work on one machine and th e rema inder o n another in which ca s e the fixture should be so made that i t can be adapted for u se on both machines Th e re may even be ca s es when the range of sizes is s o great that two or more fix tures may b e nece s sary one of which can b e us e d on one machi ne and the ot her on a diff erent one ; or they can be made inter changeable providi ng the speeds on both machi nes gi ve r ang e enough to handl e the w ork Th e se p o int s should b e car e fully consider e d The accuracy r e qu i r e d in t h e fi n i sh e d work S hould b e 3 n oted a n d care taken to provid e mea n s of up keep o n surfaces or locating p o i nts that are subject to wear There may be occasi onal in s tances on work requi ring extreme accuracy whe n i t may be nece ss ary to pro vi de mea n s of adjustm e nt for truing u p the fixture so that it wi ll a lway s run pe rf e ct ly conc en tri c wi th the sp in dl e o f th e machi n e 4 Rigi dity in work hol di ng d e vi c e s a n d t ools sh o uld r e ce i v e ca reful attenti on ; an d overhan g from the spin dl e turr e t or c u t off s li de S hould be ke p t dow n t o a m inimum so that chatt e r will not r e sult from lack of supp or t These po int s ne e d mor e consi derat i on when the tools a n d fixtur e s ar e t o b e us e d o n the horizontal typ e of machi ne t han wh e n a ve rti cal machin e is to be emp loyed n C lamp i g d e v i ces f or adjus t ab l e fi x tur e s shou l d b e l a i d 5 out !by m e ans of a p ie c e of trac ing p ap er) for e ach pie c e t o be handled so that there wi ll be no chance of clamp s b ein g t oo long too short or imprope rly p ro p ort i oned for som e of th e work E rrors are v e ry l ikely to occur in t hi s p art of the d e s i gn unless the greatest care is used ; and ther e are also ca s e s when the work varie s in thi ckn ess as well as in d iam ete r ; therefor e thi s p o in t mu st be ca reful ly con sider e d 6 P rovi s i on for clea nin g the fixt ur e mus t b e mad e so tha t all loca ting po int s an d su rfac es wil l be rea d ily accessible I f 2

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D E S I GN

JIG

2 44

several sizes of s tuds or l ocatin g rin g s ar e to b e us e d t hey mus t be so arranged that chi p s and dirt wi ll not int e rfere with the p roper location of the work They must also b e p lac e d so t h at they can be easily replace d or remove d The adjustments w h i ch are necessary to prov i d e for 7 handling variou s sizes of work should be carefully studied an d sui table provi sion should be made so that the changes from o n e and vari atio n s i n s etting to another wi ll always be un i form the work cannot occur due to errors in adjustment If n e cessary setting gage s can be made for the vari ous p i eces to be handled or a s ep arate set of screws or other adjustable locat ing members id m i s c an be made for each p iece and pro p erly stamped to a vo takes The nature Of the work h a s a grea t deal to do with the method used to secure uni form adjustmen ts and sp ecifi c cas e s will be noted in followin g p aragrap hs 8 C on venience and rap i d i ty of o p eration S hou ld b e gi ve n con sideration and provision S hould be made for setting up the work in as short a time as possible The fixture s hould b e so arranged that the work can o nly b e set up in the correct way and it S hould b e as ne arly fool proof as p ossible The cost of the fixture shou l d be ke p t down to the low e st 9 figure that i s con sis tent wi th go o d d e sign because the numb e r of p ieces to b e machi ned is comp arat ively small If th e work for whi ch the fixture i s mad e i s of such a nature that it i s not li k e ly to be changed a little mor e latitude is p ermiss i ble ; but as changes in design are always possib l e i t i s advi s able n ot t o make an elaborat e fix tur e 0 Th e safety of t he op era t or sh ou l d a lways b e cons id e re d n and p rojecti g lugs s e t screws or other parts wh i ch mi ght catch in hi s cl othi ng should be elim inated from the design O ther p o ints i n de sign not mentioned in the fore g o in g wil l be sp ec ifically mentioned throughout thi s chap ter ; commen ts will be made and faulty points criticiz ed and discussed The three or four jawed chuck is perhap s t h e most fre quently used of all th e holding devi ces which are adjustable to tak e vari ous s izes of work There are als o collet s of numer o us kin ds whi ch are adjustable wi thin certa in limi ts and s tep ,

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D E S I GN

J IG

246

and fin i shed pi ec e s principally for bar work or som e thing of a similar character Wh en a round piec e of work is to be mad e up in s everal S izes and is of simple form it may often be handled to good advantage in a set of soft jaws appli ed to a three jawed universal chuck These jaws are bored out on the machine to the exact diameter of the finished work and when s e t up o n the piece they p resent a good holding surface with su fficien t accuracy for the ordi nary run of commercial work Ad j u st ab l e F ix t ur e for H ol d ing Ca stings of D iffe r ent D iam S hows at A and L the smallest and larg e s t S izes F ig e t e rs of castings to be machined on a horizontal turre t lath e ; and there were two intermediate S izes whi ch were also handled on the same fix tures A special nose piece C i s scr ewed to the end of the spindle and has a hub at its forward end on which the locatin g ring B !upper view) is fix ed The fini sh e d portion of the work fits this ring at D and is drawn back aga in st i t by the collar G ; th e rod E pa ss es through the sp indl e and i s pulled back by m e ans of a handwheel at th e end whil e th e key F prevents it from turning The forward end of the rod is threaded to receive the knurled finge r nut H whi ch has a In S pherical b e ar i ng i n the collar G to e qualize th e pressure setting up th e work the piece is placed o n the locat ing ring the collar G i s slipped over the end of th e rod E and the knurled nut H is rapidly scr ewed on wi th the fingers after which the handwh eel at th e end of the sp indle is u s ed to tighten th e collar A long boring tool J is us e d to rough out the shoulder e d portion of the work and t o bore the bearing and it wi ll b e not e d that although thi s tool has considerable overhang it is well s e t up in the tool holder K an d given addi t ional strength by th e us e of two t o olp os t s The larger p ie c e L sh own in the lower part of t h e illustra ti o n i s s e t up o n th e rin g M locat ing on the surfac e 0 whi ch ha s b e en p revi ously bored A larger collar N i s used for clamp ing thi s p ie c e With th e exception of the locating rin g and collar all of the other parts of the holdi ng devi ce are the sam e as in the p rece d ing insta n c e A ddit ional rings and collar s f or th e inte rmed i at e S ize s make t h e fixture comp l e t e It wi ll be .

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AD JU S TAB LE

FI

XTUR E S

247

n ot e d

that th e re are two holes in the front of th e nose piece whi ch are so p laced that a r od may b e u s ed to dr i ve off the locat ing rin gs when chang in g o ver th e fixture for anoth e r s ize of work Thi s fix ture i s S impl e and comparatively inexp e ns iv e -

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H l d i g B l-g Bl k f V i u S iz y et i t i s adap t e d for use on four piece s of work of different S izes and th e chang e s required are of such a nature that they may be perform ed quickly so that th e re i s very little loss of time It may fut h e r be noted that the boring tool is the same in F ig 2 .

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F ixt

ur

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for

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e ve

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ar o

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248

J IG

D E S I GN

each ca se and that the adj u s tment for diff er e nt diameters is obtained by the cross sliding mo vement of the t urret B Ad j u stab le F ixtur e for S pe cial e ve l g e ar B lanks The work A shown in F ig is a special be vel gear blank and these gears are us e d in a gr e at number of s ize s on textile machinery The pieces were held in the firs t setting by the i nterior and were machined on the sid e having the be veled surface and on the periphery ; they were al so partially under cut along the edge of the rim in order to p rovide a clamping s urface during the second s etting E xtreme accuracy was required i n the work and yet there w e re so many S izes to be handled that the con of s ep arat e fixtures was deemed inad vi sable A s tructio n S pecial fac e plate B was therefore de s i gned having thre e radial doveta il slot s C !uppe r vi ew) in i ts face ; and a small portion F of each of thes e slots was l e ft straight to assi st in locating the movabl e jaws D These jaws were mad e of steel and were radially adjustable t o vari ous di am e ters be ing clamp ed in any d e sired posi tion by means of the screws G and the do vetail s hoes E A numb e r of set s of soft steel supplem e ntary j aws H were drawn back into a seat on the main jaws by the two screws J and were bored in place to the d i ameter of the out side of the gear the main j aws being set in place to a n approximation of the correct diameter in each instance The clamps K were drawn down upon th e fini sh e d portion of the work by means of th e screws L in the j aws A bushing M was set in the c e nter of the faceplate and us e d as a guide for the pilot N of the boring bar P which was held in the turret The tool 0 was used to bore the hole whi le the tool Q faced the unfini sh e d portion of the gear blank the latter tool being held in two t oolp ost s R on th e cut off S lide In handling some of the larger g e ar blanks a supplem entary h e ad T !lower vi ew) was placed on the end of the boring bar and held in place by the screws U on th e fiat t e d portion of the bar Thi s head gave good support to the tool S wh i ch was used for boring the larger sizes of gear blanks Thi s tool was held in pla ce by the s crews X and V the latter pa ss ing through the hole pro vided for it in the bar F ine adj u s tment s were provi ded for in the .

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F ig 4 .

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bo ri ng ,

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H l di o

f cing a

,

ng

and

D E S I GN

h S iz f S t l Fl cutt ing P cking G v

T

re e

es o

a

ee

ange s ,

wh il

e

roo e s

The s crews N are set in to the ring from th e rear a n d ar e located in different place s for the variou s rings The fixture has three T s lots G in order that the clamp s E may be con ve ni e nt ly adjustable by means of th e T bolts F wh i ch en ter .

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S ABLE

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the se slots The boring and shoulder work performed o n the p i e c e i s accomplish e d by th e shove l nos e d tool 0 wh i ch i s moun t e d in the tool holder P o n the turr et T hi s is an example o f a fix t ur e d e s igne d for sta n dard work of various S izes coming t hrough in small lots and wh i ch requ i r e s extreme accuracy in machinin g The fix t ure i s a comp act desi gn and i t i s built cl ose in to t h e sp indle so that a l though the fix ture i tself is heavy th e re i s so li tt l e ove rhan g t hat the we ight i s of small imp ort a n ce Th e Ad j u s t ab l e Fixt ur e s for th e Ve r t i c al B or ing Mill t ab l e of a vert i cal boring m il l i s so arra n ged that i t may be us e d ei ther as a facep lat e or as a chuck wi th provi sion for clamp ing in t h e T-S l ots wh en ne c e ssary Th i s i s a di sti n ct advantage in ma ny kinds of work and espe c ially so wher e a numb e r of pie ces of s im i l ar co n struct i o n a n d d iffer e nt siz e s are t o b e h a n dl e d F ig 4 shows a s imp l e fix tur e for ha n dling thr ee S iz e s o f s t e e l flanges A Th e bas e C o f the fixt ure is made of ca s t ir o n an d i s c e nt e red by a p lu g D in th e table hole ; a n d i t is f as tene d down to th e t ab l e by m e a n s of th e scr ews F which enter sh oes in the T sl o t s I n th e upp er i llustrati on the work A has be e n pr e vi ousl y turne d fac e d a n d partially under cut t o pro vi de f or cl amp in g and i t i s h e ld during th e first s e tt ing by means o f jaws o n t h e in si d e of the flan ge On the s e co n d s e t tin g !shown in th e up p er i llustrat i o n) the ope ra ti on s p erform e d consist o f bor ing t h e hole facing the flange as far as th e cl amp s and cutt ing the packing groo ves O The loca ting rin g B i s slippe d o n th e fini shed port i on of the bas e a n d i s drawn down by th e screws E The clamps H are supp or te d a t th e ou te r e n d b y th e wood en blocks K and are drawn down upon the work by nuts and wash e rs J through t he m e d i um of the T -bolts G wh i ch ar e adju s tabl e rad i ally in t he t abl e S lots The bori ng bar L i s us e d for borin g th e interior of the flan ge wi th th e tool M w hil e th e s ide h e ad !not shown) f ac e s the fla nge a n d cuts the p ack ing groov e Th e l ow e r illus t rat ion shows the fixture adapt e d for hold in g t h e larg e st piece i wh ch i t handles In this case the r i ng i s made of some N Q wha t d iff erent shape so tha t i t wil l locate properly on the .

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2

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z

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W or k whi c h h as b e e n b or e d ol e s d r ill e d in F l an g e

of

H fini shed portion of the ba s e C All other portion s of the fixture are th e same as in the preceding in s tance the clamp s H being moved outward in the T slot s a su fficient amount to take care of the work of larger diameter The tool s for boring facing an d cutting the packing groo ves P are al s o the same .

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54

DE S I GN

tion cut approx imately central with th e cored ho l e at Y F our hole shav e also be e n jig drilled at J Two S izes of the s e brack e t s were made several time s each year in lots of t e n or twelve so that the expen s e of a comp l ete fix tur e f or machini n g e ach pi ece .

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would hav e been excessive in view of the number Of pi e ces produced The following equipment proved s atis factory : An angle plate B is tongued on the under side F to fit one of the table T slot s and is held down by s crews !not s hown ) The .

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AD JU S TABLE di stanc e E

FI

X TUR E S

2

55

f or

the two s izes of bracke ts is e asily d e t e rmi ned by placing a stud G i n the cent e r hole of the table and locating the angl e plate B from it The bracket i s placed in position on the angle plat e so t hat the to ngu e H fits into th e groo ve -

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an d the bolts J ar e passed through th e hol e s in the brack et a n d tightened by the nut s at K A l i ttle freedom is a l lowed in the bolt holes and the finished e dge of the bracket res t s on the pins C Two special j aws Q ar e .

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fix ed in p osi tio n o n th e t ab l e bu t may b e adjuste d radi ally when nece ssary to brin g t h em int o the corr e ct p osi ti o n for the other s iz e of bracket Th e jaws are p rovi d e d wi th set scr ews O whi ch are adjusted t o supp ort th e ove rhanging e n d o f t h e bracket a ft e r which they are l ocke d by th e ch e ck nu t s a t P The j aws are k eyed at S to th e sub jaws of th e table ; a n d th e clamps N ar e used o n th e unfi ni shed port i on of the bracket being t ighten e d by the nuts a t R so that t h e surfac e t o b e ma chined is clear of int erfer en c e s Th e boring bar L i s u s ed to bore the hole an d th e S i de head t ool M fac e s t h e p ad Thi s is another example of a table bein g us e d wi th a fac ep lat e havi ng adjustable moving parts on i t The Ad j u s t ab l e F ixt ur e for a B r onz e Wormge ar S e c t o r fixture S hown i n F ig 7 was d e signe d t o ha n dl e t hr e e size s of the bronz e worm gear sectors A Th e bas e B of the fixture i s c ent ere d on th e t able by m e an s o f th e s tud G in the c enter hole and i t i s clampe d secur el y by m e an s of thr ee scr ews P which ent e r shoes in the table T slots An adjustab l e V block C i s mou n ted on a fini shed pad a n d ton gued o n th e u n der s i de to fit the slo t D All the jaws o n th e tabl e chuck ar e removed and a special jaw K i s substi tut e d for one of th e m Thi s jaw is S lightly u n der cu t o n i ts fac e to ass i st in hold in g down th e work an d at the sam e t ime i t forc e s the hub of th e cas t in g up into the ve e locating b l ock A S lot 0 i s cu t in t h e bas e of the fixture in order to allow the n ecessary movem en t for thi s jaw The hub rests o n a h eadl e ss set-scr ew H whi ch i s tapp ed in to the bas e and two oth e r adjusti ng screws ar e provi ded at J These are adjusted by m ean s of a wr e nch after the jaw has b ee n tightened The set screw H howeve r rema in s set after it has been adjus te d to su i t th e parti cular pi ece which i s b eing ma chined A dri ving screw at L takes t h e thrust of th e cu t and may be remove d a n d place d in either of t h e holes M or N when u s ed for the oth e r p i eces In settin g th e V block for an other dia me te r of hub it is o nl y ne cessary to loosen the screws F and move th e block radially to the desi r e d p osition The jaw K is readil y set to siz e while th e scr e ws J an d L ar e p lac e d in hol e s provided for them -

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de signs wi ll be described so that the vari ous de vice s shown may be applied to a wide range of work It is well to state that i n conn e ction wi th the applicati on of the floating p rincip le the greatest care must be u s ed in the de sign in order to mak e sure that it is correctly applied as i t is quit e po s sible to obtain a float in s ome portio n of a devi ce or tool which bein g of faulty con s truction w il l not produce the results de sired Important P oint s in th e Applic ation of th e F loating P rincipl e In order to obt ai n the mo s t s atis factory r e sult s in it s app li ca t ion a few point s are here noted which are worthy of attention As appl i ed to clamping or holding methods the greate s t car e must be u s ed in order to make sure that the float ing action i s not constra ine d in any one direction but w il l o p erate equally well a n d wi th uni form pre ssure on the requir e d area F ric t ional res i s tance may at time s be s u ffi cient in cases of this k ind to cau s e imp erfect work by reason of unequal pre s sures o n the work itself When the clamp ing action is appli ed to a rough surface still greater care mu s t be used in t hi s regard a nd th e amoun t of float must be so proportioned that i t will tak e care of a consi derab l e vari ation in the ca s tings or forgings Wh en a great number of p ieces are to be handled s everal pattern s are often used and the s e will be found to v ary s omewhat so that there are slight diffe rences i n the re sulting castings F or thi s reaso n due al lowanc e must b e made 2 Whe n app l ied to methods of locating th e work or as supp ort ing p oints on whi ch i t re s ts the con s truct ion mus t b e su ch that i t wil l not by any p o ssibility cause di stortion If s p ri n g s are us e d under sup porting plug s which are afterward t o b e l o ck e d in p ositio n the spri ng s mu s t be proport i oned so that they wi ll n o t be strong enough to cau s e a n y trouble by forcing the p i e ce out of its tru e p ositi on Al so when support s are placed against fini shed surface s they S hould be so arranged t ha t t hey wi ll not injure them In locat ing a p iece of work from two pr evi ou sly machined surface s whi ch are i n di fferent planes the float action mu s t be very carefully studi ed so that the con t acts are pos i ti ve ly a s sured and no til ting of t h e work will .

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re sult There are occasional in stances which requi re t h e l oca tion of a p iece of work from a p reviously machined surface in connection wi th a thr e aded p orti o n by which i t must be clamped “ In a case of thi s ki nd th e float mus t be made so t hat i t will .

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Pi t D il l J ig h ing F l ti g Cl mp take car e of a p ossible la ck of co n centri ci ty between the thr ead and t h e oth e r fini sh e d surfac e s and a t the same t im e p rovi de means of equalizin g var iati ons i n th e al ignmen t o f th e t hr e ad L ock i ng dev i c e s for float i ng m e mb e rs must b e so ar 3 ranged that the members can be pos it ively locked or clam p ed wi thout cau sing any change in the i r po si ti on s A turni ng F ig 1 .

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2 60

JIG

D E S I GN

action such as m ight b e caused by th e e n d of a scr ew agains t a locat ing point is often sufli cie nt to throw the work out of i ts correct position The interp o sing of sho e s between screw s an d floatin g m e mbers wi ll p r e vent any t rouble of t hi s k ind O th e r p o ints in construct i on and de s ig n will b e note d in conn e ct ion wi th the examples to be descri b e d P i s t on Dr ill J ig with F lo ati ng Clamps A v e ry g o o d ex ample of a drill jig whi ch i s p rovi ded wi th a float ing cl amp to work on a rough surface i s shown in F ig the work b ein g a pis ton cast ing A whi ch has bee n p revi ousl y mach ine d at B The body of the j i g G is of sem i box sect i on and i s p rovi ded wi th feet D on whi ch i t may b e rested both during the l oading and when under the drill A hardened and groun d s te el s t ud E is let into the casting at one end and serves as a locat in g p o in t for the machi ned int e ri or of the p i ston B A stud C i s f urt her p ro vid e d to gi ve the correc t locat i o n to th e wr i s t p i n boss e s As t h e e nd of the p i ston i s of sp herical shape and in the rough stat e al so it i s ne cessary to p rovi de a means of clamping whi ch will so adjus t it s elf t o t h e inequali t ies of th e cas ting that an equa l p ressur e will b e obtai ned so that there will be no t e ndency to t ilt the work A heavy latch M i s p ivoted on the p in L and i s slo t ted at the other e nd t o allow the passa ge of the thumb screw N whi ch i s used to clamp i t i n posi ti on A sp e ci al screw 0 i s t h re ad e d in to t h e lat ch and i s bal l en ded at P s o that it has a spheri cal beari ng aga inst the float in g c lamp Q The screw S keep s i t in p osition but i t wi ll be noted tha t clearance i ded t o a l low for the float in g moveme n t around the body is pro v of the scr ew Thre e p in s R are set 1 2 de gr e es ap art in th e face of the float in g clamp so tha t a firm thr e e -p o in t b e aring is assured In order t o a ssi s t i n s upporting the work un der th e p re s sure of the dri ll two s pring p ins T are provi ded these bein g set in t h e form of a ve e near the front end of the pi s ton They are encased in a screw bu sh ing U and are l ocked in p osi t ion by m e ans of set screws not shown aft e r they have b een allowed to sp ring up against th e p i ston casting !In order to avoid confus ion in the drawing one of the s e p in s is shown at an angle of 4 5 degree s from i t s actual posi tion ) .

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other work has been don e upon i t the S i des b eing l ef t in th ei r natural forged shape Six holes ar e t o be dr il led around the rim as S hown at N and it will b e s een that som e care i s ne ce s s ary i n th e locat ing and clam pin g arrangem e nts so that the resulting hol e s will be parallel wi th th e axi s of t h e col lar The j ig body C i s of cast i ron and i s p rovided wi th a harden e d a n d ground st eel l ocating col l ar B on whi ch the p revi ously machi ned interi or of the ring i s locat e d Th e ring i s p laced o n this steel collar restin g again s t the single s teel bush i n g D whi ch i s i ns e rted in t h e body of th e j ig Two oth e r bush in g s E ar e arranged h t c oil sp rings 2 0 d e grees apart a n d are provid e d wi th very li g whi ch forc e them u p against th e un d e r s ide of t h e ring Th e shoes F ar e then set up aga inst th e angu l ar cut o n t h e s e bush ings H by m e an s of the scr ews Th e smal l s et scr ews G b e ar aga in s t th e fla t t ene d s ide of th e shoes and p r event th em from turn ing I t will b e n o te d that the angula r cut on th e body of the bushings is such as t o preven t th em from p ushi ng down under the pres sure of th e drill The bushin g plat e J i s locat e d o n t h e s t ud Q an d i s p r e v ent e d from turn in g by the pin K whi ch fits th e slot L i n th e bod y of the jig S ix bushings N ar e set in to the plat e at e qual in tervals A nu t P a n d a C washer 0 p ro vid e for r e ady removal of the plate an d draw i t down solidl y o n th e top of th e locat ing rin g B Th e three pointed screws M are s et in to t h e work sl ightly to prevent any change in its location It i s w ell to n o te that i t would have cost no more to machi n e one si de of th e work while it was being bored thus obvi ating th e n e ce s si ty of th e floating locat ing bushings Dr ill J ig with F l oat ing B u sh i ngs and Lo cati ng Ve e s A somewhat p eculiar condit i on i s S hown in F ig 3 the work A being a be llcr ank of ordinary constructi on such as is used i n large quantiti es in automobile work There are som e in s tances o n work of thi s k ind when a vari at i on of 5 7 inch or mor e i n th e c ente r to c enter di stances i s not consi dered of ext reme imp ort anc e but i t i s quite i mportan t t o have the holes as near t h e cent e r of the bo ss e s a s po ssible In order to counteract variation s in the ca s tings and s till obtain hole s which are central .

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THE

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on th e bosses it was n e cessary to adopt s ome sort of float ing co n structi o n such as that S hown in th e illustratio n A number of jigs of t hi s kin d ar e in us e in a l arg e automob il e factory and their act i on i s ve ry sat i sfactory In t he instanc e shown the work i s l ocated o n a stud J from th e previ ously r e amed hole in the hub It s hould al s o b e noted that both hub s and bos s e s have been faced to S ize previous to the drilling operation A ,

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D ill J ig wit h F l ti g B u hi g d L c t i g V sliding V block Q i s carefully fitted to the slot E in the body of th e jig and on i t is mounted the bush ing plate P in which the bushing D i s carried A fter the piece has been p laced in posi tio n th e S lidi ng block is p u shed forward by the operator unt il th e ve e C com e s up again s t th e boss on th e cast ing and locat e s i t Th e thumb scr e w F locks the block firmly i n p o si t i on an d the sli d ing clamp G holds th e work A nother block S i s a l so cut out i n the form of a ve e at L but i s no t F ig 3 .

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tongued on its lower side to fit a S lot a s in th e oth e r insta n c e A bus hi n g p lat e R i s mounte d on i t wi th a bushi ng K a t the forward end The under si d e o f th e block has two n arrow bear ing surfac e s N an d M an d it i s free to swivel in any d ire c t ion re quire d by the slightly varying p osi ti ons of the bos s ,

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F ig 4 .

M illi ng F ixt ur wi th F l e

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C l mp a

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The thumb crew 0 holds it in place after i t has b e e n located by the operator Th e other clamp H i s then us e d to hold the piece firmly A drill j ig of thi s kind i s n o t su it e d t o a ll classes of work but i t pro v ed s atisfactory in thi s case ; the fl o a tin g action gives excellent results when absolute accuracy in the product is not requi red -s

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ing Pr e s s ur e Compe n s ato r The work A shown in F ig 5 h a s been part ially machined in a p revious operat i on and th e flange has also been drilled so that one of the holes can b e used for dri ving purpos e s The machi ne to whi ch thi s d e vi c e i s applied i s a turret lath e of the horizontal typ e and th e body B is s crewed to th e spin dl e en d C in the u sual man ne r The pin T i s set into a boss in th e face of the fix ture and acts as a dri ver in o ne of the flange hol e s Two steel rin gs F and G ac t as approximat e locators for the work when it i s first p lac e d on the fix ture Two cy lind ri ca l st ee l cams H and J are accurately ground to fit the cen tral hole in the fixtur e an d ar e op erated by the rod M whi ch i s threaded right an d l e ft hand respecti vely at N and 0 E ach cam is mi lled to a 2 0 degr ee angle at K and L three of these S lots be in g equally spaced around the periphery so that the i r angular surfac e s control the mo vem en t of the locat i ng pin s D and E The coil springs retur n the pins to an in act ive p osi ti on wh en released by the cams A plug P i s placed in the sp indl e as shown i n th e illustration for the purpose of providing a s e at for the co il sp ring Q whi ch assi sts in th e r e leasing of th e pins a f ter the machi ning h as been done The two s top pin s R an d S lim i t the movement of th e cams and tak e all th e thrust o f th e twistin g actio n of the operating s crew In thi s co nne ctio n it i s well to not e that th e s e stop p in s are a ni ce fit in the cam slots while th e locating pins have a S ide Cleara n c e in the an gular slots of inch so that th ere i s no p oss ib ili ty of trouble be in g caused by frictio n a t these p oint s A tt en t i o n i s f urth e r called to the fact that the actio n of the cams i s such that a true floating moti o n i s produced wh en the screw i s op era t ed so that all of th e locat in g pins are set up wi th a n equal amoun t of pressure A floatin g acti o n of this n atur e may b e rea di ly app l i ed to ho l din g fix t ur e s for a great v ar i ety of work L ca t i Ch ucking F ixt u r e wi th F l o at i ng C l am s a n d T a e r o n g p p Plug A som e what u n usual co n di tio n i s shown in F ig 6 t h e work A b eing a sp eci al clutch flywheel which has been Lo cati ng

D e vi c e

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lugs on the int e ri or of the castin g pre vent e d th e work from be ing held in a three jaw chuck on account of interference s with the jaws A two jaw chuck was therefore utilized and inter A s the centering action of a chuck fe re nc e s thereby a voided of thi typ e is very unc ertain wh e n used for holding work by an interior surface of comparatively large diameter som e method of locating was necessary which would at the same t ime center the casting and yet not cause troub l e by i nterferin g wi th the lugs on the interi or of the flywh e e l !The lugs on th e interior of the casting are not shown i n th e il lus t rat i on in ord e r to avoid confu si on ) The chuck body B is s crewed to the spindle C in th e usual —

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manner and is provided with two special jaws one of whi ch E i of plain de ign ha vin g two bearing surfaces on the in ner rim of the fly wheel ca s ting The other D is groove d to fit the chuck like the regular jaw but i s very much wider as i t comes above the face of the chuck Thi s portion i s turn e d to a radius at H and given an angle of 0 degree s at the same t ime in order to counteract the li fting tendency which might cau s e trouble when the j aws were tightened The floating member or rocker F i s mounted on thi s jaw as shown in the illu stration and i s limited in i t s movement by the two s crews G and the elongated hole s in the rocker Thi con truction gi ve s a very good center ,

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2

D E S I GN

ing action and the rocker jaw h as sufficient float to take care of variations in the ca s ting Pi s t on Ch uc k h aving F lo ati ng Clamping F e atur e s The work A shown in F ig 8 is a large automob ile pi s ton which h as been bored and faced o n th e open e nd to a predetermined concentri c s ize and whi ch is to be completed in thi s sett i ng and s quare wi th the fini shed porti on P revi ous to this s etting and after the borin g and facing operation th e wrist pin hol e i s rough drill e d in a j ig in order to facilitat e th e holding of the work on the fixture The cas ting is located on a hard ened and ground st e el r in g F which i s forced o n the body of the fix ture B and a small annular groov e on the ring prev ents trouble or e rrors in lo cat ing whi ch might be caused by the presence of chi p s or dir t on the locating surface The body of the fixtur e is held in place on the table of the machine by th e bolt s C whi ch enter the table T-slots and it is ce nter e d on th e table by the plug D whi ch is forced into it at S The clamp ing p in L is ball ended and h as a spherical p ortion in the center also It is slott e d at N so tha t the pin M i n th e draw bar G will enter the S lot as i t i s pas s ed t hr ough the wr i st p in holes and bring up aga in st the shoulder so as to center the clamping pin in the p i ston A great deal of strain is taken by thi s clamp ing p in and for this reason it i s made of tool s te el and spring tempe r ed so tha t ther e wil l be le ss chance of br eakage The draw bar G is also of tool steel and i t is ke yed with a Woodruff key at H to prevent it s turn ing the key being a slidi ng fit i n the body of the fix ture The lower end of the rod i s threaded wi th a 4 pi tch A cme thread double left ha n d to fit the op eratin g nut Q thi s latter b eing provi ded with a handl e R whi ch ext end s out through a cored openi ng 0 i n the fixture Th e p e rm i s sibl e movement of thi s handle is suf ficie nt to produce a vertical mo v ement of fig inch o f the draw bar which is ample for the purpose of clamping and releasing A thru s t collar P i s interposed between the operat in g nut and the boss on the under side of the fixture and a coil spring J keep s the rod up so that the clamping pin may be ea sily placed ,

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2 74

D E S I GN

as the float ing action of the pin with i t s three point bearing equalizes all pres sures and at th e same time provide s a very s ecure method of clamp ing the work The work A Ch u ck Jaw s wi th F loa t in g Lo c a t i ng P oi nt s s hown i n F ig 9 is to be bored shouldered and faced complete in one settin g and on account of its length it was considered nece ss ary to provi de addi tional supporting po in ts bes i des the j aw surfaces A set of special jaws B is keyed to the sub jaws in the table at D ea ch speci al jaw be ing shoul d e r e d at C to support the work The brackets E are tongued at F to fit the speci al jaws and ar e secured thereto by the screws G The e bracket s act as a -

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s

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F i g 10 .

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inding F i t u

Gr

x

re

for S t e e l

C

o

ll ar s

supp ort for the steel floating ring M in which the thre e spri ng pins J are p laced E longated holes at p oints N allow t he required floating acti on the ring bein g clamped by the collar head screws The brackets on whi ch th e ring rests are p ro vi d e d with a S helf H whi ch i s o ffset s li ghtly from the c en ter so as to give the nec e ssary wi dth for th e screws In using the device the screws L and N are l oosened an d the work placed i n the jaws which ar e t hen t ightened while the ri ng float s suffici ently to allow for vari ati ons It will be not e d that the n p in s be in g sp ri g co n trolled adapt themselves to the ca s ting an d are there locked by the s crew s L after which the ring it elf is clamped by the collar head s crews N .

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TH E F

Al though

LO ATING PRI N CI P LE

27

the

5

floating acti o n of thi s d e vi c e was sat i sfac to ry t h e dri ving or gri pp in g p ower was foun d insufli cie nt to hold t h e work securel y and i t b e came ne c e ssary to re p lace the sp ring pin s wi th square h e ad set scr ews cup p o in t e d th e rin g b eing ta ppe d out to r e ce ive th em The ring was th en all owe d t o float whil e t h e s e scr ews we r e lightl y s et up o n th e w ork af te r whi ch th e c lampin g scr ew s N wer e tight ene d A f te r t h i s chang e in constructi o n th e act i on o f th e m e chani sm was much imp ro ved and th e dri ving p ower was fo un d su fficient Th e w o rk A F loat ing Clam pi ng Ring o n G r ind ing F ixt ur e shown in F ig 0 is a st ee l casting whi ch i s t o be gro un d on th e tw o ext e ri or surfac e s A n ose pi ece D i s screwe d t o t he e nd of th e spindl e E and i s p rovi d e d with a hard e ned a n d grou n d locat ing rin g B on whi ch the work locates Th e s t ud C i s forc e d i n t o the n os e-pie c e and is threaded on i ts ou te r e n d to r e c ei v e a sph e ri cal nut F The collar G is concaved t o th e sam e radi us as the spherical portio n of th e nut so t ha t it floa t s aga in s t the en d of the work

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C H AP T E R X I I

APPLICATI O N

OF

TH E T IN F I

HR

— EE

XT URE S

P O IN T P RIN C IPLE

The three point principle is illustrated by a s tool having thre e legs S uch a stool wi ll be firmly sup ported even when placed upon an uneven surface which is not the case if a s tool having four legs i s used If a jig having four feet is placed upon th e table of a machine and there is a chip under on e of the feet this will cause the jig to rock wh en pressure is applied to the upper side ; but if there were only three feet and the s e were located with one foot on a line mi d way between the two feet at the opposite end of th e jig a chip under one foot would not cause a rocking mo vem e nt The jig howe ver would be tilted upward and as explain e d in C hap ter I thi s might not be noticed by the operator F or thi s reason four feet are generally con sidered preferable when they S imply s erve to support the jig or fix ture In the mechanical field however the principle of three point support is applicable to many clas ses of work and its importance is understood and made u s e of in various kinds of machine and fixture work In the auto mobile industry alignment of the working parts is pre s erved by making the power plant a self contained unit and h ay i ng it supported on three point s in order to equalize or neutralize the twi sting action caused by the pas sage of the car over the more or less uneven surface of the road If s ome pro vis ion of this kind were not made distortion of the parts would res ult and they would consequently fail to operate properly In machine design the three point principle is utiliz ed in numerou s ways S ometimes the bed of a lath e is supported on two points at one end of the machine while the o th e r has a single swiv el bearing or its equivalent The machines pro vi d e d with this feature are ea s ily set up without danger of -

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276

2

78

JIG

D E S I GN

piece on three strips instead of on a cont inuous surface in order to facili tate a s sembling When this is necessary it is advi s able to make the strip s in such a way that they can be readily replaced when worn The supporting po ints shou l d b e so locat e d that they can be e asily r e ached for cl eaning in order that locat i o n s will not be a ffect e d by an accumulation of chip s or dirt at important points A djustable p oints S ho uld b e so arranged that d irt and chip s will not c l o g the screws a n d thus mak e th e m d i ffi cult to opera te Thi s p o in t in d e sign should r e c eive car e ful attentio n when fix tur e s are de si gne d for us e on the ver ti cal t urret l athe or verti cal bori ng mill On mach in es of th e horiz ontal typ e l ess trouble i s likely to b e exp e ri enc e d in thi s r e spect b e cause th e chips do not tend to fall o n the scr ews In e i ther case however it i s always well to provi de against a ny t rouble from thi s source It is frequently desirabl e to i ns e rt hard ene d s tee l bu t to n s of uniform height in the jaw scr ew hol e s in order to ra i s e a p ortion of th e work above th e top s of th e s t an dard jaws so that t h e work can be faced or under cut The s e buttons form an excel lent thre e p o int supp ort for th e work in addit i on to pe rf orm ing th e fun cti on already m en ti on e d S hort p arallels cut from cold roll e d st eel may b e used on a ve rti cal turr e t la th e and are somewhat ch e ape r t han th e button s but they ar e O pen to the obj e cti on of becomin g easily di splaced and lost Whe n it is n e cessary to arran ge p o ints to a c t as a ve e on long cyl indri cal surfaces i t i s good practi ce t o make them so that th ey can be adjust e d t o t ake up w e ar Thi s can e asily be done by mean s of h e adless set-screws wi th check-nuts to lock them securely in any p osi ti on ; and i t i s a bett e r co n st ruction to p lac e one check nut o n th e outs id e an d another one inside than t o have both nuts on on e si de of th e fix tur e wall The const ruction of the fixture will not al ways pe rmi t of u sing thi s m ethod but when i t will very sati sfac t ory resul ts are obtained Wh e n the three po int support i s appli ed to th e fix ture i t s elf the clamp screws whi ch hold th e fixture in place on the table should be arrang e d at the po ints where the supports are placed ,

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THR E E

Appli c

P O I N T P R I N C I P LE

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p

P i ci pl

279

h l di ng F l ywh l whi l n d F cing O p p f m B ti n any clamp s for th e work it sel f shou l d b e as ne ar th e same Fi g 1

Th r e e - oint ing oring or

at i on of er

and

—

r n

a

a

e

in

a

o

e ra

ee

e

o s

plac e as p ossible Th r e e po int S upport for F lywh e e l F ixt ur e Th e fix ture for the motor flywheel S hown at A in t h e upp e r p ar t of F ig has a three po int support Th e flywheel is of such a d iameter that a s in gl e supporting po int i n on e of th e chuck jaws wou l d .

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2 80

J IG

D E S I GN

not b e sufficien t to resis t th e p re ssur e of th e cuttin g ac ti o n of the variou s tools us ed in mach i ning The work is h el d by the insid e in the sp e cial jaws B whi ch are r e lieved at E to p ermit th e back-facin g of the rim Th e tools L and K whi ch ar e held in a sp eci al tool b l ock o n the cut off sli d e ar e us e d for back facing and fini sh in g the p ad ; a n d othe r tool s !n o t shown) in the turre t fac e the p orti on W of th e flywh eel Th e bor ing bar I has a pil ot H whi ch ente rs th e gui d e bushi ng G in th e chuck to give gr e ater accuracy an d rigi di ty Two o f th e jaws are provi ded wi th spring p ins C whi ch are re l e ased an d l ocked by the action of the screws F o n the sho e s D The stop -pin in the third jaw i s fix e d in ord e r t o give p osi ti ve l ongi tud in al loca tion of the work Work of thi s ki n d i s ve ry frequ en tly l ocat e d on the thr ee fixed en ds o f t h e jaw s a nd grippe d b y th e in si de as shown but wh en thi s i s d one the r e i s always a chan ce of in correct holding and p ossi b l e s lipp ag e du e t o spring o f the casting S ometim e s t hi s resul ts in the p roducti o n of grooves or a wavy surface on th e outsi d e of th e work In the seco n d s e tting of t h e work a fiXt ure i s us e d an d th e p o in t of locati o n is th e r e c e ss whi ch has bee n machi n ed in the firs t settin g Thi s locates th e pi ec e on a p lug M which is shouldered at N and fits a ho l e p rovi ded for it i n th e cen ter of the fixtur e Th e p re vi ously machine d surface W r e sts o n three pin s P whi ch ar e of unif orm h ei ght and so arrang e d that they leave a sl ight cl e aranc e b e tween t h e fac e of the p lu g M and the face of the S houlder o n th e work Th e fixtur e body 0 is screwed to the spindle and i ts exteri or forms a con t in uous rin g S so as to make thi s surfac e cl e an an d avo id danger t o the op erator through project in g lu gs e t c The work i s drawn back agains t the pin s P by means of th e clamp s R throu gh the medi um of the screws Q Work of this kind i s fr e quently held and drawn down upon a cont inuous fin i shed surface in st e ad of a s eries of p in s The d isadvan ta ge of a cont inuous surface i s that dir t collects upon i t and ren d e rs loca tion un certain u nless great care is taken to keep the fixture clean The fixtur e shown h r T e e point F i xt ur e for a P ot C a s t i ng at H in F ig was arranged to hold the ca s ting A which is .

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2

D E S I GN

I J G

282

taken t o s ee t ha t th e amount o f cl e aran c e i s amp l e to tak e care of any co n dit ion whi ch might b e foun d An in ch of clear The p ot ance all around is none too much o n a large cast ing fix t ur e H is centrally locat e d on th e table by the plug J and i s fastened down by the T bolts O in the table s lots Th e set screws at B and C se r ve as locat ing p o ints for th e casting There are two screws at B and one at C the la tter being locat e d mi dway v ert i cally bet ween th e ot h e r two and degrees from them Thi s is somewha t contrary to th e usual 0 9 custom and in some cas e s might n ot b e found d esirab l e for example when con siderable dep endenc e has to b e p laced on the locating s crews to a s si st in dri ving the work In th i s case however ample provisi on for dri vin g i s obta ined Th e work is forced o ver again s t p oints B an d C by the central set screw D of the thre e shown Wh en th e cast ing has been brou ght up snugly into p lac e th e upp e r and l ow e r screws D are also tightened P rotection against chip s i s p ro vi ded for in con ne c t i on w i th thes e set scr e ws no p ort i on of the thr e ad E be i ng expo s ed The work rests o n a fixed po in t G !shown in the upp e r vi ew) which act s as a p o si t ive st op Two addi tional p o ints F are adju s table by m e an s of a wrench and th ei r t hreads are protected from di rt by a cyli ndri cal portion above The openings P in th e wall of the fixture allow access for t he screws ; the U-clamps L draw it down upon the poi n ts by m e ans of the nuts and washers M o n the stud s K The cl amp s L b eing of U section ar e r eadily removabl e wi thout requi ring the nuts and washers to be take n off The p lan view shows onl y one clamp in posi ti on in order to S how thi s clearl y Two M e th od s of O b ta ining a Th r e e -point S uppo rt on a H ub Cas ti ng T he work A S hown in the u pp er p ort i o n of F ig 3 is a hub cast ing of large s ize a n d the method to b e described was first sugge st e d in connecti on wi th the han dl ing of thi s work The ide a was abandoned however in favor of t h e m e thod shown at th e lower part of the illustrati on In the up pe r illus t rat ion th e jaws C are mount e d o n the ra i s ing blocks E and tongued to th em a t D while th e rai s ing blocks are ton gued and f asten e d t o t he sub jaws of th e tabl e at F Three hardened .

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TH RE E

p o int s

—

P O I NT P RI NCI P LE

2 83

ar e s et in p roj e ctio n s of th e u ppe r jaws a n d the work res ts on t h e s e p o ints A supp l em en tary cas ting G i s ce n t e r e d on t h e tabl e by m e a n s o f th e hol l ow p l u g M w hi ch a l so act s B

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F ig 3 .

.

O ri g

in

l

a

and

I

mpr

ove

d M th e

p

od s of

Th r e e - oi nt S

l

h o d ing

u pport

L

arg e

H ub Casti ng b y

as a gu id e for th e borin g bar pi lot O ; an d the u pp er p art of thi s bush in g i s b e veled as shown bu t t h e edg e of th e hole i s l e ft S harp so tha t chips wi ll not be drawn down wi th the bar an d ten d to destroy i t t og e ther with the bushin g Th e bas e of -

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2 84

D E S I GN

J IG

the fix ture is slotted at three p oints H to all ow t h e ne cessary movem ent of the jaws ; an d th er e ar e t hre e lu gs mi dway b e twe en the jaws on th e base in whi ch th e sp rin g pin s J are carried A fter the work has b e e n c en t e red by t h e jaws these pins are releas e d and allowe d to come into co n tact wi th the work ; they are the n l ocked by th e se t scr ews L The borin g bar P i s of the multip le type having two tool s Q and R for the two in si de di ameters The too l Z i s carri ed in the upper part of the S ide head instead of th e l ow e r in ord e r t o e cono miz e on th e l ength o f the borin g bar A s the purp ose of three supp orting p o in ts J w as s im p ly to steady the work i t was thought that a simpl e r d e si gn would answer all purposes an d th e p r e vi ous m e thod was ther e fore abandon ed in favor of the o ne shown in th e l owe r p art of In thi s cas e the bushin g T i s us e d di rectl y in the center F ig 3 hole of t he table and the boring bar i s made corr e s p o n dingly The rai sin g blocks V ar e also l ow e r tha n in the pr e s horter an d ar e keyed to th e sub jaws a t X in the same vio u s case manner The con structi o n of the jaws C i s i dent i cal in both cases Thre e spri n g plungers S wi th knurled end s W are in serted in the jaws and tightene d in any desired posi tio n by the s e t screws Thi s method i s much s imp l e r than the other a nd po s sesses U the added ad vantag e s of be ing both cheap er and mor e e fficient F ixt ur e h avi ng Th r e e Clam n i J w t i a s d Th r L o c n a n e e a g p g P ad s The work illustrated at A in F ig 4 has b een partially bored and fac e d an d i n th e s e tting shown i t i s nece ss ary to work from the p revi ou sly fini shed surfac e s The base cast ing E is slotted to r e cei ve the three stee l locating jaws C on which the finish ed surface B locates Th e s e jaws are held in place by the scr ews D and ar e carefully fini sh e d aft e r being drawn into pos i tion The base is c entered by the plug F in the table hole G and is held down by the screws Q in the lugs P on e of which is shown in the plan vi ew Three p ad s H are fini shed to support the flange an d a dr iver J is ins e rted in on e of the s e pads The work i s clamped by m e an s of th e hook clamps K in order to keep the di ameter of the fixture as s mall as possible ; and a cap s crew L passe s through the hook clamp ,

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286

I J G

D E S I GN

by th e interi or cored surface Th e bas e B i s mad e of cast iron and is c en tered on the table by m ean s of the hollow plug C It is h eld down by scr ews D whi ch en t e r sho e s in t h e t able A

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.

Mach i ner y F ig 5 .

M e t h od

of

h oldi ng

a

Pi e

ce

of

Work

b y an Int e ri or Core d S

urface

The uppe r portion of th e fix t ur e E fi t s a ci rcular to ngue F on th e bas e to which i t i s fast ene d by th e screws G Th e upper portion E i s S lott e d to r e ce i v e the jaw s N and O T S

l ots

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HRE E

-

P O I NT P RI N CIP LE

287

and ther e ar e thre e p ai rs of jaws s e t 2 0 d e gr ee s ap ar t Th e uppe r p or ti on of the fix ture E i s made sep arat e i n ord e r to facili ta te the machi n ing of th e sl ots Two cyl in dri ca l cams H a n d J control the radi al movem en ts of th e jaws by m e ans of the scr ew K whi ch i s thr e aded wi th a coars e p i tch left han d thr e ad in the l ow e r cam a n d a ri gh t han d thread in the upp er cam The uppe r end o f the rod i s squar e d at L and i s operat e d by a sock e t wren ch M In order t o p revent the ent ry of chip s and di rt into th e m e cha ni sm a f el t washer S i s fas tene d t o the upp er cam; an d s teel cove r-p la te R i s p l ac e d o n top o f th e fix tur e and h el d in p l ac e by screws The harden e d st eel pi n T strik e s a gain s t the inne r cor e d surfac e a n d l oca te s th e pi e c e ve rt i cally S lo t s ar e cut in th e uppe r p orti o n of th e fix tur e E to a ll ow th e i nsertio n o f th e flat sp rings Q whi ch throw the jaws back int o p o si ti o n up o n wi thdrawin g t hem f rom th e work ; an d a sh eet s teel cover-p late P k eep s t h e di rt out o f th e s e sl o t s Th e cams an d screw ar e suppo rt e d by the co il sp rin g shown b el ow t h e l ower cam a n d the acti o n o f th e cam s i s limi ted by the s cr ews U whi ch ente r s l o t s in th e cams Th e s e screws al so s e rv e t o p revent the r evo luti o n of th e cams A comb inat i on bori n g a n d r eaming bar W i s us e d for borin g an d reaming th e hol e wh ile the o utsi d e surf ac e s ar e mach in ed by vari ous t ools i n th e si d e he ad o n e o f th e se b ein g shown at V I n t h e co ns t ructi o n of thi s d e vi c e it will be n o te d t ha t al t hough S ix p o in ts or jaws ar e us e d for l oca t i n g t h e arran geme n t i s such that they a ll b e ar a g a ins t t h e i n si de of t h e cast i ng wi th a n equa l amount o f p r e ssur e a t th e same t im e c en t e rin g the work from t h e c o r e d i nt e ri or AS t h e ri ght -and -l ef t scr ew o n th e rod K i s ro t a te d th e two cams floa t ve rtically so that th e p ressur e on the jaws is equa lized A devi ce of thi s ki n d is usefu l in man y in stanc e s wh en work i s to b e hel d from an inte rn a l cored surfac e I

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C H AP T ER X II I

SP E CIAL J IG

AN D F I

XTURE M E CHAN I S M S

ingle item i nfluences the production ra te to as grea t an extent as the de sign of jig s and fixtures The saving of a few s econds clamping time mean s an increa s ed product i on that off It is much ea ier for an operator to clamp s et s a hi gh fir s t cost h is work by tighten i ng one nut than the u sual three and aside from the s aving of time he i s expending le s s energy and works to better adv antage to him s elf and hi s employer It is u sually nece ss ary to equalize the pre s sure in a j g before N0

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i

F ig

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S

1.

i mpl

way

e

of

C l mpi a

ng a

B u hin g s

f or

D illi r

ng

applying the clamping pre ssure When equalizing and clamp ing mechani s ms are both operated by a single clamping operation the danger of clamping before equalizing the pressure can be e li minated M any object to the term fool proof but the amount of work spoiled or sprung by carele ss clamp ing justifie s care i n designing jigs and fixture s that are at least error proof in thi s respect The m e chanism s described in this chapter are selected for their sugg e stive value and only as much of th e fixtur e is shown as .

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288

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D E SI GN

J IG

2 90

variety of bu shin g s of v arious l e ngths the stud C b ein g m ad e to sui t the longest piece of work C lamp s that have a tendency to draw the work down firmly on t o the res t-p ins or s t op s are useful i n all classes of fixture s C are F ig 4 i llus t rat e s a S i mp le m e ans of accomp l i s hing th i s should be taken to see that the stop i s p ivoted above the p oi n t A The A nother a n d more ri gid de vi c e is illustrated in F ig 5 p lunger A carri ed i n p lunger B i s forced down a g ai ns t the 4 5 de gree sid e of stop C compre ssing sp ring D A fixture tha t clamp s two clamp with a down and in pre ssure is illustrated in F i g 6 ,

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s

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C l m pi g B u hi g wh th W k V i i L gt h S li d e s B are e qualiz ed by strap C and ball a n d socket was hers D and E Thi s fixture i u s eful for mil li n g and p rofiling as the clamps and s top s are below the surface of the work F ig 7 S hows two down and in clamp s equalized for holding a round p i ece o f bored work for a mi lling opera tion Lever A i s tapped to re c e ive screw B an d the clamp ing pre s sure equaliz es with lev er C by mean s of rod D L evers A and C impar t a down -and in p ressure to p lun g ers E This fixture can be app lie d to flat w ork I n the double movement clamp s hown in F ig 8 the clamp A is carried by the hinge B pivoted at C S crew E gives c l amp A F ig

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3

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D E SI GN

2

9I

a down and in movement by means of a 4 5 -degr e e t ap er o n stud The stud D is milled off at F to give the clamp suffi cient D movement to remove th e work A mechani sm for drawing down both end s of two p i eces b y mean s o f a sin gle nut i s illustra t ed i n E ach piece i s clamped i nd ep enden t ly thus maki ng i t F ig 9 suitable f or u se on rough cas tings or forgin g s R od A running through the fixtur e carri es ball and-socket washers at each end and draws the end clamps B and C together These clamp s are — i n given a down and mov ement a g ai nst the 4 5 degree w e dg e ends of rods D and E Th e clampin g thrus t a gai nst rods D an d E impart s a downward movement to the i nner clam p s G an d H -

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F ig

4

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ra

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ng t h e

i ml y i

F r P ns

i m pl m

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e an s

W or k

th e

An t h Ex mpl f C l mp D wi ng t h W k d wn F ir ml y nt t h L c ti ng P i n

for

F ig

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a

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er

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pulling the work down on the i nner re t pins Th e clamps are return ed by means of plungers K a n d spring J Th e fix ture illustra t ed i n F ig 0 shows a method of drawing do wn two clamps and thro wing the work agai nst the stop pin by a single clamping operati on Tighte ning nut A clamp s down clamp C and pulls up rod B against the 4 5 -degree tapered end of rod D giving a lateral mov emen t against p lunger E P lunger E i s carri ed by the floating stud G On th e u p per e n d of stud G i s a 5 -degree taper that op erates agai ns t plunger H P lunger E im p ar t s firs t an up ward movem e n t to floatin g stud G which s

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292

D E SI GN

M ach i ner y F ig

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Fig 7 .

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l am p s

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F ixt ur e h avi ng Two Eq uali zing Cla

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wi t h

J IG

2 94

D E SI GN

a center clamp that gives a downward and ou tward t hru s t by mean s of the taper e d end s of plate A whi ch is carried by plunger B P lunger C wedge s down the p lunger D which is tapped into p lunger B P lungers B and D are held up F ig

i llustra t es

I 2

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of

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by a sp ring E A small pi n i n p lung er D allows a half turn o f plunger B so that the work may be lifted ou t In the fixture i llustrat ed in F ig 4 the work !two clutch S hells) is equalized and clamp ed by a single mo v ement of the handwheel .

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mp s and F or ci ng th e m ping O p rati on

for r awi ng o wn Two Cl a n s t th e S t o la p i n b y a S i ngl e

p

C

e

drawing out rod C again s t the collar D The section A A s hows how thi s collar equa lize s its thru t with plun ger s E and F The collar D i s free to slip to either side as required for e qualizin g The plunger E and F draw in rods G and H through B,

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J IG

D E SI GN

295

the m edi um of collars J and K The s trap M held c entral by a small sp rin g and p lun ge r equaliz e s the p ull on the center cl amp A ll clamp s are mad e to c l ear the work when it i s to be r e mov e d by means o f th e l ev e r L and the sys tem of l ev e rs shown in the lower view .

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Fig

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11.

Fi xt

ur e

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qu ali zi ng t h Cl am pi ng S m all W s h s e

a

Pr e s s

ur e

on

Ei gh t

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gs 3 an d 5 i llus t rate a small double mov e m e n t c l ampin g mechani s m for h and mi lli ng or p rofiling us e I n F ig 3 the clamping pressure agai ns t clamp A also p ulls ou t p lun ger B throwing u p plunger C and throwi ng the work aga i ns t stop E by means of plung e r D S pring plunger G i s used to re turn plun ger D In F ig 5 the pull through clamp A on p lunger B Fi

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F ig

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ove or

D ES I GN

a

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D E SI GN

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the clamp i s hook e d over the flange C are must be t ak en tha t the p oint X is below the p ivot point of the pi e ce C F ig 7 illustrates par t of a heav y milling fixture for clamp i ng agains t the stop plate A by mean s of the two p lungers B and C by equalizing with the p lunger D a n d sleeve E working against P rojectio n s on the work B and C with 4 5 degree wedge cut s often prevent the u s e of plain clamps F ig 8 shows a re s ort .

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15.

er

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l am pi ng M e c hani s m

C

to an u nusual but effici en t clamp to meet the s e condi ti on s The use of plungers A and B permits the clamp to be operated from the rear by mean s of a screw C and knob D When work is long in proportion to i t s width or when the locating pins mu s t be placed clo e together as in the piece illu s trated in F ig 9 there is danger of it cocking or binding between one locating pin and the s crew if a plai n screw i s used to throw th e work ,

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D E SI GN

2 99

again s t t h e loca ting pins Th e use of a roller instead o f a scr ew pr ev en ts thi s T h e roller A wi ll turn until the work s t rikes bo th stop pins In the de vice illustrat e d B and C are the fixed locati n g pins an d D the clamp screw t appe d into the bushing .

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qual izi ng

of a

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op e ra tin g t h e sli din g p lunger G It i s obvi ous tha t the work c an b e p reve n t e d f r o m b i nd ing b y us i n g tw o e qua lizin g p lu ng ers to throw i t agai nst the locating pin s i nst e ad of a roller F ig 2 0 S hows the locating mechan i s m for a milling fix ture in whi ch two pie c e s are located by two p lung e rs each all op era te d E

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0 0 3

F ig

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18

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3

02

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D E SI GN

concav e surfac e o n an un usua l pie c e Th e wo rk i s c l ampe d agai nst the pads A and B on previ ously m i lled surfac e s by mean s of two di fferentially op erated p lungers C and D simi lar to a pre vi ously d e scribed devi ce To prevent spri nging u n der cut the work i s backed up wi th th e floating p lunger E on the one side and F and G on the other The plungers are op erated by push-rods H and J These push rod s are han d op era te d an d are clamp ed by the bushi ng K and star kn ob L .

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22.

Fi xt

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M illi ng a C ncav S ur fac e provi d e d wi th u pport s und e r th e M ill d S u f c

for S

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occasi ons ari se i n whi ch the 4 5 -degree p lung e rs do n ot permi t of suffici ent c l ampi ng move men t The m e chani sm in F ig 2 3 was designed to o v ercome thi s objecti on An unusually larg e movement of t h e clamp is requi re d to clamp directly over the r e st pin Rod A op era t ed by scr e w B i mp ar t s mov em ent to both p lung e rs C and D P lunger C p ulls clamp E down and plunger D pushes up on clamp E through the p lu ng er G The wedg e angle b e twe e n p lungers C and D s hould be less than that between plu ngers A an d C There i s consi d e rabl e fric tion i n thi s mecha ni sm .

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u u ll y Lar g M qui r e d

Un s i s Re

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v e ry rigi d m e chanism for clamping a t three p oin t s by m eans o f one scr ew i s shown i n F ig 2 4 I n thi s cas e it i s shown app li ed to a drill j ig but it i s rigi d e nough t o pe rmit i ts use in milling or plani ng fixtures In th e se ca s es th e clamping pins A

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04

D E SI GN

b e come re s t-pins an d are subject to the thr ust of th e cut S cr ew The de t ai ls of this A thrust s against equali zing plunger B p lunger mechani s m are illu s trated i n the e n g ravi ng P lunger B i s of le ss di ameter t han the dri lled hol e and re s ts o n th e piece C Thi s piece i s cut from a rod of the same di ameter as the hol e and is u s ed to afford a fla t base for plunger B to re s t on and in sure .

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2

5

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A S i mpl

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E

j ct i n g e

D e vi

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full contact of the wedg e end a gain s t the plungers D and E P lung er G i s a duplicate of B and e qualize s the plungers F and H by means of the same mechani sm C on siderable sav ing o f time may b e eff ect e d by the use of ejectors F ig 5 is an examp le of the u e of an ejector P ush rod A h as four notche s milled tapering on one end The pins .

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C H AP T E R X I V

PRO VID IN G

F OR

UP KE E P

I N DE S IG N IN G

X

J IG S

AN D F I TU RE S

The impor tan c e of p rovi ding for upkeep in th e d e s ign of the anu fa c t u i ing work ca nn ot vari ous typ es of fix t ures us e d in m be over-empha sized In many cases p rovi sio n for upkeep can be incorporated in t h e desi gn without increa sing the first cost of the fixtur e t o an y gr e a t ex ten t whi l e in other instan ces con si derabl e extra outl a y may be ne cessary M uch dep en d s upon th e accuracy requ ir e d in th e finished p roduc t and th e numb e r of pi ec e s whi ch are to b e machi n e d F or examp l e in gun work whe n grea t quant itie s of p ar t s ar e t o b e produc e d no expens e i s sp ared i n making t h e fixtures in as durab l e a mann e r as p ossibl e and in making p rovi si o n for the rep lac e ment o f worn l ocatin g p oint s e t c On machin e t oo l work howeve r d i screti o n mu s t be ex e r ci s e d so tha t the expense of fixtures may be consi ste n t wi th t h e r e qu i r e d ra te o f p roducti o n and accuracy of the work M an y factors i nflu e nc e des ign in thi s r e gard Th e size an d gene ral character o f t h e work d et erm in e th e t ype of machin e on which t h e fixture i s to be used an d there fore the n e ed for stabil i ty and s tre ngth The number of piece s to b e machi ne d i s a factor which must b e co n si der e d for i t i s a pp are n t that a small number do e s n ot requi r e an y speci al car e to b e taken in regard t o t h e mat t e r of upk eep In drill j ig work the locatin g points bushings and feet may be mad e so that t hey can be readily rep laced wh en abus e or w e ar o f thes e p ar ts tends to cause imp erf e ct work The p robab l e ne c e ssi ty for r ep lac eme nt s i s na t ura ll y d e t e rm ine d by th e rate of p roduc ti o n that i s re u i red J ig s a n d fixtures ar e often handled rou g h l y and th ey q should b e co n struc te d to wi thst an d such u s age Millin g fixtures are frequently requi re d to s t an d v e ry heavy cut tin g s o that .

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PR O VI S I O N

F OR

U

P KE E P

0 3 7

gre at rigi di ty i s an imp orta nt f e ature in th eir constructi o n In th e cas e of horizo n ta l t urr e t lathe fixtures or others which re volve abou t a fix e d c ente r i t may frequently be found d e sira ble to ma k e l ocatin g rings po ints or surfaces in such a way that adjustm ent can conv enien tly be made abou t this center .

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F ig 1 .

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D ill J i g f r

or a

Re

c e iv r F e

or gi ng

i P e rtai n ing t o Upke e p A few noteworthy p o in ts of co n s t ruct i o n are given herewith : Location of the work Thi s is of primary i mp or t a n c e an d the vari ous fixed p oints provi d e d in the fix ture should b e m ade in such a way tha t they ca n either be read ily replaced or adjusted accordin g to c ir P o nt s

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0 8 3

D E S I GN

J IG

mst ance s 2 The n umber of piece s t o b e machine d should receive p rope r consideratio n in the design both i n regard to co s t of the fix ture and in regard to p robable n ece s s i ty of re placements 3 Weight and rigidity of the fix ture This point i s naturally somewhat dep en de n t up o n th e class of w ork for whi ch i t is intended an d th e co nveni ence of ha n dling 4 Gib s In th e cas e of ind exi ng or slidi ng fixture s suitable p ro v isi on should be made for adjus tmen t by mea ns of gib s or straps in order that natural wear may be taken u p 5 R ev olving fix tures F ixtures whi ch revolve about a fix ed ce n ter if subjected t o hard usag e or i f u s ed for a great n umber of pieces may be advantage ously p rovi ded wi th m e ans of adju s tment about the c enter of r e volution Thi s i s a r efin eme n t that is very infr e quently used and i t i s n ot nec e ssary in the majority of cas es unles s extreme accuracy i s r e qui red Ther e are a few p oints in con struction which are app li cable p rincip ally to individual cases Th e se w ill b e referred to later Dr ill J ig for a R e c e ive r F orging T he work A shown in F ig has been p revi ou sly faced milled and bored and tapped at the en d K leavin g four holes C D E and F to b e drilled o n the jig S hown in the illustration This type of jig is built up en ti rely from st ee l p arts a rectan gular plat e formi ng the base of th e j ig The work i s laid down o n the harden ed pin B an d the heads o f the two j ig bu shi ngs C and D whi ch are ground to a uni form surface The thr e aded plug at K is p rovi ded with a knurl e d head L and draws the end of the r e c eiv er up again s t the s teel block N whi ch is screwed an d doweled to th e j ig base A thrust washer is pro vi ded at M and a slight float is allow e d betwe en the b l ock and the p lug The s tud G is screwed into the p late an d the s e t screw H ru nning through i t forms an adju s table stop for the si de of the rece iv er check-nuts being provided at J After the work has been drawn up by the threaded plu g at K the set-screw in the s tud P i s us e d t o p ush the work over again st the po int H The st e el cl amp O i s sl i d into posi ti on an d ti ghten ed an d the set -screw R in the swi nging clamp Q at th e other end of the work is brought to b e ar a t that point The clamp Q is cu

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rounded so tha t di rt or chi ps can not lodge o n them an d caus e faulty locating Th e pin D S im p ly acts as a stop for locatin g t h in ternal boss e s o n th e work ; a n d fe et are provi d e d at B so that the jig casting can b e s et u p on t his end for l oading purp oses A swin ging clamp J i s provi ded at th e op en end of the j ig and this clamp is p rovided wi th a rocke r G whi ch pivots o n the pin H slot K being cut for i ts r e cep ti on A sw in gi n g clamp scr e w i s l oca te d at L whi ch w orks in the the nut an d wash e r at M being S lot on the e n d of the clam p J us e d to draw i t up firmly An e qual iz ing acti on i s obtain e d in t hi s manne r o n th e swive l H so th at p r e ssur e i s equally di s tributed on th e en d of th e castin g As i t was n ec e ssary during the machining of thi s pie c e t o use s eve ral s iz es of tools a n d to work from both sides of the cast in g i t was found advi sabl e to use liner bushings P in order t o p r e ve n t un due w e ar Thes e bushings ar e hard ene d an d grou n d a n d forced i nto posi tion ; an d the slip bushings Q are slott e d t o r e cei ve the pin R to pre vent th em from turning Th e st ee l s tuds N an d O o n opp osi te sides of th e j ig body ar e groun d t o a u ni form surfac e an d act as f eet f or th e j i g I n conn ect io n with t hi s j ig i t i s w ell t o n ot e tha t al l p arts subj e ct to w e ar are r e adily rep lac e ab l e thus making the life of t h e j ig almost ind e fini te Ind e xi ng F ixture for a Clutch G e ar In e very kin d o f in d exi ng m e cha ni sm o ne of t h e chie f po in ts in d e si gn i s to pr e vent vari ati ons in th e spacing due to w e ar o n t he m e chani sm Th e fixtur e shown in F ig 3 i s so arranged that w ear on the ind exin g p oi nt s i s automati ca lly take n u p by the cons t ructi o n of the d evice so that th e p rovisi on mad e for i ts upk e ep is excel l en t I n addi tio n to thi s f e a tur e the d e s i gn i s n ot ve ry expen sive and it may be mad e up at much l e ss cost than many other kin ds of ind exing devi ces Th e work A i s a clutch gear th e clutch p orti on B of whi ch i s t o be mach in e d in thi s s e tti n g As t h e work has b een previ ously machi ne d all ove r it i s ne c e ssary to work from t h e fin i sh e d surfac e s The body of th e fix ture G i s o f cas t i ro n an d i t i s p rovi ded wi th two machi ne st ee l keys at P ; th e s e k e ys locate th e fixture o n the tabl e by means of th e T S lots and the hold down bolts Q lock it securely in po sition The revolving portion of the fix .

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PRO VI SI O N

F OR

UP

KE E P

3

1 1

ture F is also of ca s t iron and has a beari ng all around on the base whi le the c e ntral stud C i s u s ed as a locator for the work at i ts u pp er end and holds t he re volving portion down firmly by means of the nut and collar at H The fittin g at this point is such that the fixture may be revol ved readily and yet is not free en ough so t hat there is any lo s t motion A liner bu shi ng of hardened steel i s groun d to a n i c e fit on the central stud at E ,

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C l u t ch G an d will wear almo s t indefinitely whi le an indexing ring L is forced on the re volving portion F of the fixture and doweled in i t correct positi on by the pin V and held i n place by the four s crew s R The work i s held down firmly on the re volving por tion by means of the three clamps J the s e being slotted at K to facilitate rapi d remo val A steel index bolt M of rectangular section is care fully fitted to the slot i n the body of the fixture and beveled at its i nner F ig 3 .

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d e xi ng F ixt ur u e d f M illing T

In

e

s

or

e e th

in

e ar

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s

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2O

J

3

J IG

1 2

D E S I GN

end S so that it e nters the angular slots S and T of the index rin g C learance is allowed between the end of the bolt and the bottom of these slots so that wear is automat i cally taken care of A stud O is screwed into the under side of the index bolt and a stiff coiled spring at N keeps the bolt firmly i n po sition The pin U i s ob vi ou sly used for drawing the bolt back and i ndexing the fixture P oint s worthy of n ote in the construction of t hi s fixture are the liner bushing at E the steel l ocating ring L and the automat i c method of taki n g up w ear by th e angular lock bolt M The work shown at A in F i xt ur e with Ins e rt e d Jaws F i g 4 is a steel casting whi ch has to be finish e d on the in s i de .

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F ig 4 .

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provi

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for

H l di ng o

or

Th e s e cast ing s are made in two sizes one of which i s i nch larger than t h e other It w as desired to us e the same fixture for both pieces in order to avoid the exp ense of making two fix tures !Th e larger piece of work i s shown in the ill u s tration ) F or th i s purpose a fix ture D was de si gned to be screwed to the end of the lath e spindle in the u sual manner There are four jaws B which rest i n slots around the in side of the fixture the se jaws be ing drawn back into their seat s by the screws C in order t o b e ground in place to the correct di ameter B eyond the e nds of the j aws th e pointed hollow s e t screws H are so placed that they will com e opposite to the web portion of the casting I

,

.

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-

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3

I J G

14

D E S I GN

crewed to the nose of the spindle while the other C is adjustable on the fir s t piece In the illu stration piece C is S hown clamped firmly agains t the body B of the fixture by the steel clamping s

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,

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Fi g 6 .

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i u

F xt

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re

for

H l di o

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P art

i ll y F i i h d C n s

a

e

as tin g

A

ring D and the s crews E and it will fu ther be noted that there i a slight clearance between the out ide diameter of the body B and the in ide of part C Three set crew F are equidi tantly r

,

s

s

s

-

.

s

s

s

PRO VI SI O N

F OR

UP

KE E P

3

1

5

placed aroun d the periphery of the ring C and thes e s e t screws are furnished with check nuts as shown B y looseni ng the collar D and manipulating se t s crews F the worki ng p ortion s of the fix ture can be readily trued up when they b e come slightly out of true through u se or abuse A steel locat in g ring N is forced on the ring C and i s ground to the s iz e of the interior gear The method of clampin g is somewhat out of the ordinary con sisting of th e use of thre e clamp s G and an operating screw J and a floating collar K The three clamps are placed 2 0 degrees apart and have slightly o versize holes through whi ch the screws H pa ss Th e s e screw s have a ball surfac e on the under s ide of the collar corresponding to a S imilar depre s si o n in the clamp s themselves A steel bu shing M is fitted to the body B of the fix ture and i s threaded with a coarse p i tch thread which corresponds to that on the operat ing screw J A fter the clamp s G have b een swung into place on the ring g e ar a few turn s of t he screw J set s all three of them with a uniform pr e ssure through the medium of th e sph e ri cal collar K whi ch bear s again st their inner S ides A lthough a fixture of thi s ki nd is somewhat expen sive i n first cost all the parts can be r e adily replaced at a minim um exp en s e and the fixture may also be kept true with the center of rotati on of th e sp indl e wi th ve ry little trouble F ixt u r e for a H u b C as t i ng The work A S hown in F ig 6 i s a hub casting whi ch has b e en pr e vi ously machin e d o n th e surfaces B C and D The fixture E on whi ch it is held for s ubsequent operat i on s i s made of cast i ron i t i s center e d o n ; the table by the plug F and h e ld down by the s crews G which enter the table T slots A steel locating ring H is forced o n the body of the fixture and forms the point of locati on for the work Three studs J are s e t 2 0 degre e s ap art i n the base ; and they are surface ground to the correct he ight to support the work Th i s arrangement make s locations po si t ive regardless of chi p s or di rt The clamp s K hold the work down on the pin s J F eatures of t hi s fixture are the ease of replacement of th e locating rings and poin ts and freedom from troubl e which might b e cau s ed by an accumulat i on of chips or di rt -

-

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j ig all o w anc e s for grind ing and l apping ,

jig arb or fo r jig d riving fit all o w anc e s jig for rose c h uck ing re am e r s t abl e jig grind ing and l apping jig h ar d e ning jig m at e rials for jig m e t h o d of m aki ng jig sc re w t yp e jig s t at ionary d im e ns ions of jig u se d a s l oc a t i ng m e ans jig wh e e l s for i nt e rnal g ri nd ing lini ng t ab l e o f di m e nsions loose m e ans for p re ve nt ing t h e m f ro m

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qui pp d wi t h fl t ing bu h ing nd l c q uipp d wi t h mi lling t t ch m nt oa

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l nge jig nd l c t i ng v pp l ie d t d i ll j ig F l o t ing b u h i ng f pi t n ch uck F l oat ing cl m p ing f t u F l oat ing cl am p ing ing on g ri nd ing fixt u pp li d t o mi ll ing fi t u F l at ing cl m p s nd l o c at o F l o t ing cl m p and t p l c t ing p lu g f ch u cking fixt u F l oat ing cl m p s pp l i d t o p i t on d ri ll ji g t wo j w c h u ck F l o t i ng j w f F l oat ing l c t i ng p oi nt f ch uck j w s F l oat ing p e ss ur c o m p ns t f l c t i ng d v i c e pp l i e d t fi xt u w k F loat ing p inc ip l e s im p ort nt poi nt s in app li c t i n F lywh e e l fixt u e t h re e p oi nt u pp t F ork li nk s d rill jig fo

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j u st ab l e for w o r k ad j u s t abl e b o r ing ,

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23

3

I ND E

24

fl

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