[anoel]

I just finished converting my X axis on my Taig lathe to use a leadscrew and a stepper instead of the Rack and Pinion. I used a double shaft stepper and put a hand crank on the other side of the stepper so that I can use the Lathe manually.

I've got the spindle sensor set up so that I can use Turbo CNC for threading.

I've still got to add a stepper to the cross slide. I think that I know how I'm going to go about it. But we'll see....

Then a variable speed DC motor for the spindle comes next for low speed torque.

What I'm curious about is threading... What spindle speeds should I be looking at for threading? I don't expect to do much of anything any more coarse than 16tpi.

I'm still a good month out before I'm ready to really dig in with cnc lathe work so I'm just trying to get a grip on some more preplanning. to make sure that I'm not over looking anything critical.

Any advice from you guys that have done mini lathe CNC conversions is welcome.

[HuFlungDung]

Anoel,

If you are using carbide tools to thread with, you most likely would want to thread in steel at around 300 to 400 surface feet per minute. Cutting speed is fairly important in steels because of the "critical speed", which is the speed at which the chip flow is the best. Generally speaking, when turning at or above the critical speed, the turned surface is smooth and shiny, but if you are below the critical speed, then the surface is rough, and the insert suffers greatest wear and abuse from built-up edge occurring continuously on the insert.

This translates into some pretty high rpms for small diameter work, which may be above the synchronization speed of your machine with the spindle encoder. So you may have to settle for whatever you can get. Generally, thread at the same speed as you would rough turn at.

Threading aluminum, well there is no speed limit. Fast is good.

Use a declining depth of cut on successive passes, to reduce the chip load and heat on the final passes.

[Klox]

Hu, I always enjoys the answers you post! You always gives the info fact by fact so that there's no confusion.....i couldn't have put it better!
On my conventional lathe i use the 4:1 method of cutting threads (to reduce the hammering on the insert) but for the rest the above mentioned info applies.....

Klox

[msobik]

I'm interested in converting my Taig as well. Can I pick your brain?

- How did you add a leadscrew and is it necessary?

- How did you add the spindle sensor?

- Tips on mounting a stepper on the z-axis?

Thanks for the info!

Mike

[anoel]

For the Leadscrew I made a stepper mount that attached to the board. (Had to make a new mounting board.)

I removed the Pinion and hand wheel fro the carriage and cut a delrin block and drilled a hole in one end and attached it to the carriage with a 10/32 screw where the pinion setscrew was originally. Then backed the carriage up so that I could line up a mark with the stepper shaft. then removed the block and drilled and tapped the block of the shaft mark for a 1/4"-20 threaded rod. I made a thrust bearing mount for the other end of the rod to accomodate a 1/4" ID bearing that I had on hand.

To do the spindle sensor I drilled a hole in the headstock pulley and epoxied in a small rare earth magnet. Then used a hall effect switch mounted on the headstock so that it would be triggered by the magnet as the spindle rotated.

I've not addressed the Z axis yet. I'm going to convert the Spindle motor to a DC unit before I do the Z.

[msobik]

Thanks for the info, Nathan!