Ball screw and electronic lathe conversion

[tonyfoale]

The only real limit should be swing, center distance, and beef to support full size material at correct RPM. Serious spindle bore? Just a fuzzy dream.

...... so many haven't a decent taper attachment, a favored spindle, speed range, metric threading; yaddy-ya. ......

Could not agree more with your limits. I have an MT5 taper in the spindle so the bore is large for the size of the machine.
Theading with the conversion is so easy. It doesn't care whether it is metric, imperial or other strange units. it is just a question of specifying the pitch. So in metric if I want a M1.5 thread I just enter 1.5, if I want (doubt that I ever will) a 16 tpi then that is a pitch of 1.59 and so I enter 1.59.
In fact in terms of data entry there is no difference between setting turning feed and thread pitch. When threading the only difference is that the Z axis is advanced on each pass so that it follows the thread angle. 60 deg needs an advance of 0.577 times the depth of cut for that pass. When doing multiple passes the depth of cut for each pass is automatically set such that each pass removes the same volume of material.