Quote Originally Posted by claytume
Can you guys with lathes cut 25tpi?

I don't have a job for you but many years ago I was asked to make adaptors for lens cells into a shutter, 25tpi.........couldn't do it and never seen a lathe that had that pitch on it.
I'm pretty certain my lathe, with 16 TPI lead screw, can do this if I have the right gears (or order some inexpensive spares) for the change gear train. If I haven't bent my brain, I'd need 50:20 compounded to 50:80, but I don't think the original change gear set includes two 50 tooth gears. It'd be dead simple on a larger lathe with the very common 10 TPI screw, if it's got manual change gears, just a 20:50 or equivalent pair and enough no-change to complete the train.

It's very common, however, to find lathes with quick-change gearboxes for which there either doesn't exist a manual change train, or more likely the manual gears were put away years ago and no one now in the shop has ever seen them. Since 25 TPI isn't a standard thread, it's not found in most QC boxes.

The most modern of the small lathes have "electronic lead screws" using shaft encoders on the spindle, counter/divider systems, and stepper motors driving the lead screw, to cut any thread, either metric or inch, that you can specify -- right or left hand, front or rear tool post, inside or outside. Need to cut a 28.6 tpi to match some bizarre non-metric thread found on something? No problem...