"go to zero" isn't going to zero

[fbmstar]

When I press the "go to zero" button in mach 3, the dro's don't actually go to zero. This only seems to happen if the machine is close to zero at the time.

If i'm within .002" of zero, and press the "go to zero" button, the motors don't do anything, and the dro doesn't move either.

If the machine is between .003" and .040", and i press the "go to zero" button, it'll go to somewhere between .0001" and .0017". It seems random as to the number it'll stop at, but it never goes to zero. this always happens if the axis is within around .040" of the zero. If the axis is above .050" and I press "go to zero", it will always go to zero on the dro.

The steps per are 30480 on the y axis, and 20320 on x and z axis, which should give theoretical resolutions of .0000328" and .0000492".

All the numbers above are the numbers showing in Mach's DRO, not measured machine postions.

Any ideas on what is causing this?

Thanks,

Brian