Re: Ball lead screw backlash problems

Thanks for the suggestions fellas, it turns out that it is a problem
with the thrust bearings.

After disassembling it, it became clear that the "semi-pro" that had
installed the ballscrews had hacked things a little. The Y screw
preload wasn't set correctly and the way the motor mount was
designed you couldn't adjust it. I reworked it so I could set some
preload using shims and got the 0.004" Y backlash down to 0.001",
same as the X axis.

Increasing the preload any more didn't get rid of the last 0.001",
but the machine has 6204 plain ball bearings in place for these
thrust bearings, and when you put in ballscrews you're supposed to
upgrade those bearings to 7204 angular contact type, which handle
thrust loads more accurately, so the last 0.001" is probably due to
these bearings. I doubt its wear in the screws as the machine hasn't
been used that much and was only used to cut small thin pieces of
aluminum.

The thing I was worried about is the "semi-pro" that did the
retrofit didn't put any limit switches on the machine, so when I saw
the large backlash I was afraid the machine had been run hard into
the end of the screw, but it looks like that wasn't the case
(needless to say I'm adding limit switches to the machine).

I'll leave it as is for now, 0.001" is good enough for the time
being, and I'll upgrade it to 7204 bearings at some point down the
road.

Thanks again for the help fellas, I feel a lot better knowing my Y
ballscrew isn't shot.

Paul T.