I have a question for dkowalcz

[CNCadmin]

I like your Lathe conversion to CNC? Do you have any detail pic's of the conversion.

http://www.dakeng.com/lathe.html

[dkowalcz]

Thanks, I'm glad you like it!

So, I can snap a few today, since I have it apart again for some housekeeping. Computer's got a bad power supply that wants to fail soon, I can smell it!

What are you interested in specifically? There's a whole page long article on the X axis backlash comp:

http://www.dakeng.com/backlash.html

If there's more general interest in the pictures, I can add them to the article as well. 'Bout time I revised it - it's been the same for a few years now.

[CNCadmin]

I just want to see more details on the conversion of the x and y.

[dkowalcz]

Ok, here are some pictures I managed to snap this morning.

Just a nitpick: the cross feed axis is X, and the axis along the ways is the Z. The spindle rotation is C.

Here's the Z axis motor and sundries from an angle that shows clearly how things are working. Nothing I can patent there!

I believe that's 1/2" 6061 plate or somesuch. There are a few shims underneath to true it up to the level of the leadscrew end. The coupling is a helical type that came from Winfred Berg ages ago.

As I recall, since it comes with 3/8" bores on each side, I took it to work to bore out the other side to 10mm or whatever the leadscrew end is journaled to. All the feed gearbox junk has been removed.

[dkowalcz]

Here's as good a shot as I can get for the X. There's a slightly different principle of attachment at work here.

The coupling from the gearbox to feedscrew is rigid. The motor more or less hangs on that, and the bent "L" of aluminum constrains it from rotating (a toggle link) while allowing some flex in the mechanism and extra support. Gearing is around 3:1 as I recall - haven't been inside there in a while.

Note that in the Z axis shot above the power resistors for the X axis drive are clearly visible. If I were converting this today, I would use a Geckodrive or Xylotex drive module.

Hope this sheds some light on the subject. Mounting motors isn't really anything to get too excited about - although you should be careful to avoid using the motor bearings to take up leadscrew thrust loads. The manufacturers of steppers typically don't control the end play very tightly, so it can add to the backlash in the system.

This lathe is 11 years old now, and I'd have to say it's pretty beat, but it has aged well. I'm not sure if I'd buy a HF lathe today for a CNC conversion though.

[balsaman]

Dave,

What sort of controller do you use?

Eric

[dkowalcz]

Originally posted by balsaman Dave, What sort of controller do you use? Eric

Well, TurboCNC of course! In fact, I developed it specifically for this machine at first.

[balsaman]

Dave,

Of course. I meant hardware. What driver board for the steppers.



Eric

[balsaman]

Never mind,
I see you made your own.

Eric

[dkowalcz]

Oh, the drives! Ok... I was wondering why you'd ask what software I was using - since you're using it too!

So, the X axis is a homegrown unipolar drive made out of a pile of MOSFETs and power resistors. Originally, the X axis was a 3 phase stepper and since no one made a 3 phase drive that I could find, I just made one. When I got a regular 4 phase unipolar motor to replace it, it was easiest just to solder on an extra phase worth rather than buy a drive.

The Z axis has an Intelligent Motion Systems IB106, which is basically the same as what Geckodrive sells in their G201 now. 80V max input voltage, something like 6A max per phase at 1/4 microstep for a bipolar motor.

There's a schematic set for all this on the lathe conversion page by the way:

Lathe control schematics

As I mentioned, in today's world one is better off buying a Xylotex or Geckodrive module for each axis. Nice to see that the "invisible hand" has been at work to make such products available - it has truly made CNC accessible to many people.