Re: 3D Contouring - Loss of Accuracy

My .02 and worth what you paid for it:

I wonder if your problem isn't what you think it is at all. Are you
sure your screws aren't just getting warm and expanding? I'll
admit .012" in. is extreme but still..

If it was my machine, before I got into glass scales ($ouch$) and the
like, I would put a dial indicator on it somewhere and take a reading
on something bolted to the table. Do this first thing when you
haven't run the machine all day. Then I'd write a program to rapid
the table back and forth and let it run for 15 minutes or so, then go
back to that position and take a reading again.

We have some pretty expensive 40" x 20" VMC's at work, without the
glass scales, and we don't see growth or errors like that. We also
have one machine that's 80" x 30" with the glass scales disabled and
even that thing doesn't go off by that much. But they will all change
a little bit from a cold/warm situtaion.