Home-made CNC lathe using servos

r3292c

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This is a thread about CNC Lathe I recently built. This is my first CNC machine, and obviously, I’m not a CNC guru. Being an engineer, I prefer more practical ways of making things rather than R&D approach with investing plenty of time, money and energy. This is also why I use simple and robust ideas instead of diving deep into unique ones and solving the problems just created.


I started with Atlas lathe bed I bought on ebay. This bed has pretty wide (1-1/2”) flat ways, so one can easily put the linear bearing rails on it.
s-l1600 (2).jpg

I use THK HRW-21 slides. The rail is 37mm wide, so it uses the whole width of the bed ways. The slide block is 21mm tall (with a rail) – this is a low-profile series. I think it’s important to use low-profile one here because the overall heights of the “sandwich” limits the maximum swing over carriage. The same HRW-21 slides are used for X coordinate as well.

I put ~1/2” aluminum plate in between of Z and X rails. I milled the surfaces and made the threaded holes to mount the slides on the plate. The X-screw supports are also mounted on the plate. The milling was done on my manual EMCO machine.

DSC_2700.JPG

There are some essential parts I bought in LMS online store. These are: the headstock casting, the spindle with 4” flange, and the milling table.

headstock.PNG

Spindle.png

Mill_table.png

I didn’t buy the headstock assembly because it goes with 3” spindle, ball bearings and other stuff I didn’t need (gears, etc.). I installed roller bearings. The riser blocks were made to rise the headstock by 1-1/2”.

1605 ballscrews were installed on both coordinates. The bed has about 42mm spacing between the ways. So 40mm wide ballnut fits perfectly.

DSC_2719.JPG

DSC_2729.JPG

To be continued with Drives and Tooling.
 

BaronJ

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Hi r3292c,

Looking very nice ! I'm watching with interest.
 

Eddyde

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Nice work! Please keep the pictures coming:encourage:
 

RJSakowski

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Welcome aboard! I look forward to seeing more of your posts.
 

r3292c

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Thank you for your interest to this thread. Your support inspires me to give you more details that may be not obvious.
I’m also having some difficulties translating the information to English, which is not my first language. So, thanks for your interest, for your support, and for your patience :)
 

r3292c

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The cross-feed (X-) rails are bottom-up mounted. The rails are screwed directly to the table. The threaded holes of X sliding blocks were drilled through with a carbide drill bit.

CSC_5192_comment.jpg

As you can see from the picture, X slides are exactly above Z ones. All the slides have the same exact position with a respect to each other, they don’t move. When the active tool (and the table) moves to it’s working position, it stops in between of the slides, and the cutting force is applied vertically. No bending force created, at least for reasonable part size.
 

r3292c

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I use Yaskawa SGMAS-01ACA21 servo motors and SGDS-01F01A drivers for controlling X and Z coordinates. Here is some basic info on screenshots below.

sgmas.png
Sigma3.png

HTD-3M pulleys with 4 x 1 ratio are used to drive ballscrews. Servo has x1 timing pulley, and ballscrew has x4 one. So, the ballscrew has ¼ of servo’s RPMs, and torque is multiplied by 4. As a result, the equivalent moment of inertia of parts being moved is divided by 4*4 = 16 times, what is good for overall feedback loop stability. Less powerful motors can be used as torque is multiplied by 4. However, the maximal speed is also divided by 4. If the motor can typically provide 3000RPM, the ballscrew can run at 750RPMs. Since I use 1605 screw, it gives me 5mm * 750RPM = 3750mm/min = 3.75m/min = 147inch/min maximal linear speed. This speed is probably not the best result for a large industrial machine, but I’m happy with it on my small lathe. The tool typically moves by 1-2 inch, not more.
The servo motors and drives can go to overload providing x2-x3 torque and running at 6000RPMs for 2-3 seconds. This feature also helps accelerating and decelerating quickly.

What I also like about servo drives - they don't need huge transformers for supply. They can be plugged directly to wall outlet.
DSC_2916.JPG

100W motor look tiny, it's just 76mm long. Z-axis motor.
DSC_3173.JPG

X-axis motor
CSC_5180.JPG
 

Boswell

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Thanks for taking the time to translate into English. This is a great project and I am looking forward to more pictures and details as you progress.
BTW, Welcome to the Forum.
 
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