I've seen that you can pretty easily upgrade the lathe head with taper roller bearings and jerry-rig the tail stock so you can align the centers but I have not found anyone who has done a ball screw upgrade. Is this practical at a later date for precision/removing backlash for CNC or are you better off buying into their "acu pro" line? The 4410s can be found barely used at attractive prices so I am looking. That they are still being manufactured is also a plus.
Thoughts?
I believe you have to decide what you want to do with your lathe. Historically most manual lathes have both a half nut for the lead screw and some sort of rack and pinion for faster movement or just hand-eye-coordinated manual motion.
The smaller jewellers lathes like a Unimat have a screw and no half nut. All motion is done by turning the lead screw. Very tedious. But most turning is tiny and the distances are short.
My Gingery Lathe was designed for a half nut (which I cast out of ZA-12) and IIRC, 16 TPI all thread rod. The lead screw was driven by a couple of round sewing machine O-ring belts to have power feed. But threading didn't occur until the 6th book in the series where the ability to cut gears with an indexing system was introduced. I didn't want to wait to build the shaper and mill since I had modified my drill press to be a mill so instead I developed my Electronic Lead Screw with a DB-25 parallel port cable so the lathe also worked with full CNC via MACH2 and then MACH3.
The ELS was designed to work with lathes running speeds from about 25 RPM all the way up to 6000 RPM like the Sherlines and Unimats. With that I was able to cut threads on my Gingery and a friend was able to thread with his Sherline. The Gingery lathe was retrofitted with a 10 TPI ACME screw I cut on the South Bend and I got rid of the half nut. So although not a ball screw it's definitely captive like a ball screw would be. Now it's more like the Unimat other than I have to only press a button to move it. Not as fast as the South Bend Hand wheel.
But unless you are doing a CNC based profile a ballscrew doesn't add that much. Most of the time any backlash in the half nut isn't an issue because the motion is always in the same direction. Once the backlash is taken out it stays out. Not like a mill where the cutter may pull the table away from the lead screw driving edge.
