Good thinking on holding the screw to straighten it out.I built my Joes 2006 last November and originally used 1/2" single starts for leadscrews from Enco. They were like pretzels, so I ordered 5 starts and Dumpster nuts. The Y and Z were great but the X had a wiggle in it so the cuts were not the cleanest. The wiggle also kept my speed down to about 100 ipm on the rapids.
About a 2 months ago I got another lathe that is far better than the Enco 3n1 I've had for 10 years. Being a little bored I decided to tackle the X screw and true it up. I chucked it in the 4 jaw with 6" exposed and supported the extended end through the headstock with a centering bushing. I marked the thread with a blue marking pen after dialing it as close to zero as I could get.
Then I moved the dial indicator to the end and tweaked it until it was close to zero also. (I used a long piece of shim stock on the threads so the indicator had a smooth surface) I rotated the lathe by hand. Next I loosened 2 jaws enough to slide the screw out and align the pen mark with the indicator. Moved the indicator back to the chuck and repeated the entire process again.
After a couple of 6" sections I was able to use the steady rest to help support the screw on the chuck side. Took about 4 hours to do the entire screw and I managed to get it within .002". After carefully reinstalling it in the router I was able to boost my rapid speed to 180 ipm (200 was just on the verge of skipping steps) and no decernable shake...I so happy.
Now the Y is a little off, I just think that it's jealous. Maybe I'll straighten it tomorrow....it would sure take less time, maybe not.
Guess I shoulda taken at least one picture...thought about it but then forgot. Maybe tomorrow....maybe not.