Originally Posted by
awerby
30 ipm is a pretty aggressive plunge rate for anything harder than foam. What material were you trying to cut? Usually it's best to ramp into the material at an angle, rather than plunge straight down, unless you're drilling, not milling.
But if your tool is going too deep, I think you're right, and that you lost steps on the up-stroke, not the plunge. If the latter were true, your DROs would have registered a position at the bottom of the stroke that's lower than it really was, and retreated higher than it should have from there. Have you lubricated your Z-axis slides and screws recently? Is there perhaps some material accumulated in the works? Or are the gibs out of adjustment? Could the tool have pulled out of the collet that much? If this is a new mill and it's never worked before, I'd suggest lowering the acceleration rate. But if it's been working well up to this point, I'd look for a mechanical problem.