Not so if you use a double lead ball screw on the Z axis . On my 13X25 lathe I did this mod about 15 years ago and ?I left the acme lead screw in the X axis because backlash comp handle that pretty well. I direct drove both ballscrew and lead screw with 600 oz in servo motors. The z axis ballscrew backspins eaily when I manual move the carriage. Yes you do have disengage the the QC gear box. On my machine I can disengage both. https://www.youtube.com/watch?v=vKfu-8Sv9Bw
So I built up a Little Machine Shops minilathe with Mach4 and PoKeys57 ala the Techshops design put together by Joe Katona and Ron Ginger.
Works pretty good for small stuff. Minlathe needs physical tweaking and greater rigidity. I have an Enco 13X40 geared head lathe as well where I am doing more single point threading all the time and needing to do some larger diameter tapered threads. The minilathe just does not have the low end torque. So I keep looking at the mini Vs. the 13x40 and thinking about ball screws retrofitted to the the 13x40.
My concerns and thoughts; If I retrofit with ball screws, I am under the impression that I would not be able to use the lathe in the old fashioned mode. The ball screws would allow the cross slide or carriage to move too freely or run away under pressure. Make sense?
If I replace the carriage lead screw, which one? The one for turning or threading. I could just disengage the quick change gear box. But the feed rate chart would have to be recalculated.
Other thoughts or concerns? Another lathe is out of the question.
Thought about getting a small X Y table and mount to the cross slide.
