[d_chappell]

Hi, I'm looking into building a CNC lathe from scratch and need some advice about what motors to use for the actual turning of the workpiece.

I'm using steppers for the XYZ axes, but I would also like the motor that turns the workpiece to be direction and speed controllable. Would stepper motors be up to the job of turning a lathe chuck? My suspicions are that they wouldn't. What would people suggest?

Thanks
Dave

[kawazuki]

First choice 3 phase AC - power and control, instant reverse? but won't index as well? then maybe a really big Servo motor - will have the control but not the spindle hp or then a biggish Brushless DC motor - Hp but maybe not the same control?
All depends on what work capacity and tooling requirements you require IMO

[d_chappell]

Hi, thank you so much for your response.

My initial thoughts are that the machine will be able to handle up to softer metals such as aluminium and brass. The frame of the machine I want to be constructed out of aluminium profiling, so working on harder metals would be out of the question.

I assume this will determine what hp and rpm I will require in the motor. Do you think something like a 3/4 hp, 1400rpm motor would do the trick?

The machine will be a swiss style lathe which I am able to stop, reverse and position the workpiece as i wish, so control is quite important. From your advice it seems that a servo would be the route to go down?

[kawazuki]

I'm really no expert machinist but the motor performance you are suggesting sounds appropriate for plastic, brass and ali turning but i'd be more concerned over using aluminium profile frame! First rule of turning seems to be mass/weight/rigidity and lots of it - ali doesn't have much.........although the Sherline series lathes seem to work well enough?

[RotarySMP]

Why do you want to be able to control the main spindle in Step direction mode?

If you will only be using this as a lathe, put 3 ph motor and VFD on it.

If you build it as a live tooling lathe with mill capablity, use a big servo, and servo drive.

Buiding out of aluminium profile sound like a poor choice.

Why not buy an offcut of granite from a local grave stone maker, and mount linear rails?

[d_chappell]

Why do you want to be able to control the main spindle in Step direction mode?

My intention is to be able to carry out milling operations as well as lathe work. That way I hope to be able to carry out operations similar to what you see at around 0:46 sec on this video;

http://www . youtube . com/watch?v=fW_e7LuuGWs

Buiding out of aluminium profile sound like a poor choice.

Why not buy an offcut of granite from a local grave stone maker, and mount linear rails?

I had a feeling that the aluminium idea might be an issue. There were a number of reasons why I entertained the idea; one was cost and ease of construction, the other was that I have a vague idea of making the machine compatible with this project. If you can imagine one of the cubes that they describe there with a lathe inside, then that is kind of what I was getting at.

Do you know if there are any places that sell steel profiles of the same design as the aluminium ones that are widely available? That might be a solution - albeit a very heavy one (though it seems weight is a positive attribute in this instance).

although the Sherline series lathes seem to work well enough?

I've never used the Sherlines myself. if anyone has experience of them then feedback would be welcome. From what I understand, the earlier ones had brass beds and cast bases with some aluminium parts around the place - I don't know the details exactly

Regards
Dave