Mach 3 Losing Z Position

[TaK]

Hi Guys,

I'm doing some contour roughing with a 20mil DOC. The mill does the first pass no problem, but when it goes down for the second pass, it is going much deeper than 20 mils. I hit the E-stop and checked the G-code and the position values. The G-code looks good and the read out from Mach 3 looks good too, so it thinks its in the correct location. I used my Z setter and verify that I am now more than 100 mils off where Mach 3 thinks I am.

My first thought it that my rapid between passes is too fast in the Z direction so it's missing steps or something and Mach will think its in one position when really it hasn't moved that far. I made a quick program that moves the Z up and down a few times at my programmed rapid speed and it seems to be working fine.

I verified that there is no tool offset activated and I have all the fixture offsets set to 0. I've cut several pieces using this combination CAD and CAM and POST without problems so far. The only thing different this time is that I am moving at a faster rate.

Any other ideas on what I can try to pin this down?

Thanks.

[ger21]

Lower the Z axis accel by half and try it again.