Bent Nook ballscrews ?????

Hi people.

We've purchased a couple Nook ballscrews, one directly from Nook and the
rest from McMasterCarr. All the ballscrews were slightly bent. An
email friend of mine purchased one from McMaster Carr and had the same
thing.

On Friday I increased the tension on our Z axis zero backlash ball nut
mounts. It worked OK for the machining we were doing then. However
today we are machining a different, longer part and we found that the
ballnuts are jamming on the screw, probably due to the bend. (There is
no foreign matter on the screw, etc.) Backing the tension off the
preload cured the problem.

I'm not sure that there was a backlash problem when I tightened the
preload on Friday. The parts coming off the lathe were spot on for
tolerance.

This bent ballscrew issue bothers me.

Does anyone else have this problem ?


--
Kim Lux <lux@...>