I know, I have too many projects already, but in case I am off work for any length of time, I am trying to gather the items I will need to convert my Levin watch lathe to CNC. The attached picture shows the basic layout of my Z axis. Besides the mess of my watch bench, in the picture you can see a Taig cross slide I made to fit the lathe. I had do some special machining to get it low enough to fit under the spindle. There is also I micrometer XY slide I put together. I have two ball slides that are going to be the Z axis. In the bottom of the picture you can see a spare lathe base that I will use for this conversion so I don't have to drill holes in my chromed Levin bed. I am pretty good at hand scraping now and will make sure it is better than .0001" flat.
In between the ball slides you can see the precision ACME screw I got from NOOK. It was cheaper than a ball screw but has better tolerance than most rolled screws. NOOK guarantees better than .0001" per foot. It is 1/4x20 thread. The little stepper at the end of the screw is 200 steps per revolution. This will give me an accuracy of .00025" per step. With micro stepping it will be ever better. I purchased 4 of these little steppers from eBay for $25 total with the encoders! The guy was selling the encoders and the steppers were something he threw in because he did not want to take the encoders off.
I also got some plastic ACME nuts from NOOK for the screw. I plan on cutting them in half and installing a spring between the two halves so I can get zero backlash. The loads on this lathe will be so light that it won't take much preload. The X cross slide will look similar. I have one more ball slide that I will cut in half to get me the X direction. The total X movement will be about 2", it looks like I will get almost 5" on the Z though 2" would be more than enough.
I hope to be able to make custom balance staffs when it is all completed. A balance stall might be 3mm long, 1mm at it widest, and have pivots that are .12mm.
Vince