I was playing a long time with the ideea to modify my lathe in a cnc, but I didn't like to simply add a motor to the lead screw. I always was shure that I'll use it also intensive manually. So the problem was how to turn the lead screw with a handwheel. Although it's a bench lathe, it is pretty long and if I make a smallpart, a handle on the right end of the screw were inconvenient. AND I was used to the handwheel on the carriage.
So I came to the ideea to turn the ball nut around the screw when on manual. When using it in cnc mode, the nut is locked and the stepper rotates the screw.
Of course I can use also the original gearbox for threading in manual mode, but with recalculation, since the ballscrew has another pitch.
Unfortunatelly I didn't took pictures during the construction, but I have posted a rendering of the project, just to see the principle of my ideea. I already had some 90 degrees gears, so that is why I used them. Of course some bevel gears can be used.
There are also some photos of the machine as it is now.
Sorry for my bad english,