Karl Townsend wrote:
...

if you have play in the compound nut and cannot lock the compound you
will get an drunken screw or worse.


If you're just talking about backlash, I disagree. My lathe has significant
backlash in the compound, not really a problem as the force is always in the
same direction.

FWIW, my favorite method for this job is to leave the compound set at 30.
Cut one lead. Do the math to advance the start point by backing out the
cross slide and advancing the compound to the next lead and cut again.

karl




I just did a double lead acme thread last week, with the nut. The pitch
was .250 and the lead was .500 inch. I set the compound at 0
and plunge in, since the lathe is rigid enough and it eliminates the
possibility of pushing sidewards and moving the tool. Also the lathe is
equipped with a infeed adjustable stop for threading which makes
threading a pleasure rather than squinting at the little numbers to
reset the cross slide each time.

I screwed up in that I didn't make a thread gauge for the nut before I
made it. I had to pick up the thread two times after removing the nut
from the lathe to check for fit. I left out the extra tolerance for a
long nut ( 8 inches) on a multi lead thread and that was probably why
the nut didnt quite fit on the first two trys. The shaft was 86 inches
long with the thread length about 58 inches. The nut was cast iron for
added strength I guess. It was a rush repair job for a big machine.



John