Using your Haas CNC Milling Machine as a LatHe - Twenty6 Products

Using your Haas CNC Milling Machine as a Lathe AKA: “The Mill Lathe” by Tyler Jarosz Photos by Derik Olson, drawings by Author

Problem: I first came up with the idea to turn my milling machine into a lathe out of sheer desperation. I needed to be able to manufacture long parts with both left- and right-hand threads, and my only option to complete these parts was to drive an hour and a half away to utilize a rented lathe, sleep in the bed of my truck, and work long hours. Solution: I decided to utilize the full capabilities of my Haas VF2 CNC milling machine and determine if I could use it as a lathe. To do this, I decided to chuck some 3/4"Ø round bar in my mill’s ER 32 style toolholder. Then, I mounted one of my lathe turning tools to the table of the mill, using my Kurt vise. After finding centerline of my lathe turning tool, I turned on the spindle, tried cutting the material, and it worked…I was ecstatic! Although the 3/4"Ø round bar cut, the part I needed to turn stuck out of the collet 5x the diameter of the material. From my past machining experience, I knew that if a part stuck out of the collet that far, it would need a centering or supporting device such as a live center or steady rest.

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STEADY REST I chose to design a steady rest that mounted to the spindle nose of my mill. The spindle nose plate I made has a 1.5" diameter round bar attached to it that extends down toward the table of the mill. This round bar features a moveable block on the end with a bearing pressed into it to support the material being turned. GANG STYLE TOOL BLOCK Next, in order to manufacture my parts, I needed four turning tools. I ended up designing a gang style tool block to hold four equally spaced lathe turning tools that bolted to the table of my mill along the Y-axis. I made sure this tool block allowed for five inches of turning distance. Now that I had a steady rest and gang style tool block in place, it was time to turn my parts! I tried cutting them like I did on the lathe and held onto the material by 1/2" with an ER 32 style toolholder. Upon cutting, I found that the material pulled out of the collet, due to the ER 32 style toolholders’ lack of workholding force. With the part I am manufacturing, I can only engage the material into the collet by 1/2", and I found this did not work with an ER 32 style collet.

(Note: if you are able to have full material engagement of the collet, an ER 32 style toolholder will work just fine). END MILL TOOLHOLDER To combat this part pulling problem, I designed a fixture that would hold my material in an

existing 3/4" rigid end mill tool holder. The material fixture I designed was made out of 4140 cromoly steel and heat treated to 55 Rockwell for strength. It utilizes two 3/8-24 setscrews placed 30 degrees apart with knurled ends to allow for increased gripping force. The fixture was counterbored 1/2" deep for the size of the material used, which gives me the ability to load the material consistently each time. PROGRAMMING CHALLENGES Finally, before I could try to turn my part on my “mill lathe”, I found that I had several programming hurdles to overcome. The first hurdle was Z contouring. Unlike a standard lathe, my parts had to be programmed off of the radius, and I had to utilize G18, which turned my machine from XY (G17) interpolation to XZ interpolation. The second hurdle was threading. I knew that in a threading operation I needed the spindle to orientate before each threading pass to allow the spindle encoder to align with the Z-encoder.

Spring 2009

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I found that through the use of canned cycle G76 (your standard bore cycle) the spindle would orientate before each pass. This canned cycle allowed me to turn both left- and right-hand threads. To turn left-hand threads, I would simply start on the part and thread off of the part. For right-hand threads I started off of the part and threaded on to the part. (Note: Spindle counter clockwise (M04) will not work in this canned cycle and I found that you need to maintain 8

your spindle speed below 500 RPMs because your Z-encoder will not orientate with your spindle encoder with higher spindle speeds.) CONCLUSION So, I finally manufactured my parts by using my Haas VF2 CNC milling machine as a lathe. I no longer have to drive great distances, sleep in the bed of my truck, and work long hours to turn my parts. With my new “mill lathe”, I am also manufacturing higher quality

parts due to the rigidity of the steady rest. The “mill lathe” is a win-win situation! Note: this process is not ideal for a job shop or prototype facility but great for parts you manufacture in high volume due to the extensive set up required. To see a video clip of Tyler’s mill-lathe in action, visit www.DigitalMachinist.net. To see more of Tyler’s projects, visit www.twenty6products.com.

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Bill of Materials:

Purchased Hardware:

Part Name

Material

Size

Quantity Description

Bearing Block

6061 Aluminum

1" x 2" x 1.250"

8

1/2-13 grade 8 hex bolt x 1.5"

Gang Tool Block

6061 Aluminum

2" x 4" x 14"

11

1/2" grade 8 washer

Spindle Nose Plate 6061 Aluminum

1" x 8" x 9"

3

1/2-13 grade 8 hex bolt x 2.5"

Toolholders

6061 Aluminum

2" x 4" x 4"

1

3/8-16 grade 8 hex bolt x 3.5"

Support Arm

1018 Cold Rolled Steel 1.5"Ø x 10"

1

3/8" grade 8 washer

Material Holder

4140 Steel

2

1/4-20 setscrew x 5/8"

1

3/8-16 spring plunger setscrew x 1/2"

1

1/4" x 5/8" sealed bearing

8

1/2-13 setscrew x 1/2" long

2

3/8-24 knurled face setscrew x 1/2" long

Spring 2009

1-3/4"Ø x 2-3/4"

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