Re: [CAD_CAM_EDM_DRO] move error in MACH3

chuck merja wrote:

> Thanks for the comment. And with the exception of going a long
> distance, we did do axis calibration. We only have a 1" dial indicator,
> but using MACH axis calibration in settings at 0.500" move, we get a
> 0.500" move on dial indicator. BUT THEN when we go to the MDI page and
> do a G0 X0.5 we get a 0.455" move. That's nearly a 10% error. Motors
> sound good in both cases (don't hear any missed steps, as we often do
> when we run up against mechanical limit. And again there is 0.000 to
> 0.001" backlash on this X axis.
>

Make measurements going twice in the same direction. Dial indicators
can accept
some overtravel. So, go some tens of thousandths past the zero away
from the
indicator, then go to where you have found the zero is, then move 1 "
more toward
the indicator. Then, repeat the test by toward the zero, then backing away.
You will undoubtedly get a different reading by reversing direction.
This is
the backlash (free play) in your Acme screws/nuts. I'm guessing that it
may be about 0.05", which is not astonishing on an older machine.
How have you determined there is only .001" backlash?

If the backlash really is that small, then you need to make a long move
against
a high-quality ruler. Do you have a caliper? That can also be used to
measure
travel of the machine. But, if no caliper, a good ruler should show a large
error like you are reporting.

Jon