Ok so I've got a 1978 Mori Seiki Lathe that I rebuilt and redid all the electronics and programming. Works well. Now I usually only cut short thread, 1/2" - 3/4" long, and usually 1/4-20. Then over the last few days I've been making a lot of parts using the machine for like 12 hours a day. I've always had some weird quirks with this machine and the Mach Motion built in wizards, see other posts in you're interested.
To make a long story short sometimes I have missed steps, whatever you call in with servos, so using the machine a lot lately I'm running into the problem more frequently. The machine loses steps when moving short distances using rapid. So at the end of cut when the tool goes back to X.75 Z0 (the beginning of the part) then back to home. So I figured I never cut at full speed I'll slow the servos down. I went from 80 Velocity and 20 Acceleration to 40 Velocity and 5 Acceleration to see if that was the problem. Didn't completely work, but worked well enough. The motors, mind you, were still smooth running.
So then I went to cut some 1"-8 threads that I was cutting the day before and the thread pitch was WAY off. More like 1"-20. I have no idea of why this would change anything. I just changed the motor speeds not the steps per inch.
Can anyone tell me what the deal is and how to correct this. Looking back to a couple days ago I noticed that the first 1/2" of the 1"-8 threads were pretty dam close, but 1" further down the pitch was off. I figured it was my original ball screw which is execllent, but NOT perfect. So now I realize that the pitch being off was not the ball screw but the motor speeds. As a side note when cutting lengths on Z the measurements are alwasy accurate.