Originally Posted by
Wes Grass
If you really want it in inches, ballscrews are available in 4 or 5 TPI. Not likely to find them cheap though. I checked McMaster, the screw isn't *too bad*, but the nut and supports ....
Another option is to drive the metric screw with a 47/37 tooth gear set. 4mm = .20", 5mm = .250". The ratio is accurate to the 5th decimal, significantly better than a rolled screw itself. It'll be 'backwards', and you'll have some bit of backlash in the gears, but there may a little bit in the screw/nut anyway. Just keep going in one direction til you're done.
47/37 is a 'cheap' way of cutting metric threads on a lathe with an inch leadscrew. Exact requires a 127/100 combo. Not easy to mount up on a typical lathe, and harder to source.