i am looking into cncing a small lathe &i would like to be able to do threads that it does not have gears for.i was thinking of 4 axis 1for left to right, 1 for the cross travel, & 1for the compound travel. all that i think i can do with no problems. my ? is if i am not using gears to cut threads can i use steppers on those 3 axis & a dc motor with an encoder on it to turn the spindle, or would i have to use a servo for the spindle? which ever i have to use i would also have a tach on the spindle.so can i make this work with one of these motors for the spindle & steppers for the other 3? thanks in advance for any info i may receive back. greg

It should be doable, check out MACH or DESKCNC for affordable step/direction stepper drive scenarios and, by all means, do a "lathe retrofit" search on the 'Zone.

The retrofitting of a lathe is a bit more challenging than that of a mill.

For non-mechanical linking of the spindle to the lead screw, you will need a VERY accurate timing scheme in order to do threading. This is one of the prime challenges of lathe retrofitting.

Although the "lathe retrofit" thread that I initiated some time ago is for a lathe a bit larger than what you want to do, the exact same problems/concerns will have to be addressed regarding timing, driving and steppers vs servos.

BTW, do a "stepper versus servo" thread search - the info there will answer any questions you may have about which you should use and/or why - if it doesn't answer the question, it will at least provide tech input so you can make more informed decisions.

The Mach3 Turn manual has some info about an index pulse for a lathe spindle. I think that most mach3 users doing threading use a single index pulse to detect spindle rpm, and Mach3 adjusts the other axis to accomodate the spindle speed.
http://www.artsoftcontrols.com/documentation/Using3Turn.pdf

It is really easier than you have outlined in your question.

I cnc'ed my lathe about a year ago, all you need is 2 steppers. One for you z axis, and one for your x. The compound is eliminated, you only use the cross-slide. The software can create the angles you need by incrementing the z & x.

As far as threading goes all you need is a spindle index signal. I used an optical pickup with a slotted wheel. The software uses this to determine speed and the position of your spindle. I can cut any pitch, metric, english or my own custom pitch.

Along with the steppers you will need driver cards to drive the steppers and a breakout board to interface to your pc.

Arnie

Im in the process of reliving my thread on cnc'ing a mini lathe http://www.cnczone.com/forums/showthread.php?t=27300
Maybe you can find some inspiration there, a lot have happend since my last post, but i lost my digicam along the way