Hey guys, new-ish cnc'er, have a new PCNC 1100 with the Tormach controller, generating gcode with HSMxpress and the 'Tormach_NexGenCAM_110911.cps' post processor. I'm having a major issue with Z height repeatability and I think it has to do with Mach3 and helixing and ramping. I make lots of pockets and I'm wondering how anybody else uses their Tormach to pocket and expect it to perform as commanded.

Ok, so I'll CAM my part in HSMxpress, the gcode is correct (dealing only with Z axis right now, the others are phucked the same way but not as much, if we can fix Z, I bet it fixes it all). There's a simple facing operation followed by two pocket operations on the same center, different diameter, not big deal. If I helix into the stock at 350mm/min (~15ipm) using small or large radius helix, I lose Z position by 2.5mm. I'm cutting down 2mm (0.080") at a time with a 2 degree ramp. Not every helix operation loses steps.

So I switched to a zig-zag operation instead of a helix, using only 2 axes at a time. I made two zig-zag/clear passes and lost Z again by 2.5mm; I checked the Z height with the tool on the workpiece just prior to pushing cycle start and it was fine, so Mach made two zig-zag pocket moves, picked up and moved to cut a profile and was 2.5mm too deep. So I'll run a test with a dial indicator of the table,

This is killing me, I don't trust Mach and I can't cut parts. How is this possible?

How about another approach for you awesome forum gurus: Is anybody using HSMxpress, the Tormach controller and Mach3? If so, how are you ramping into stock and what settings are you using? Can I have your post-processor settings? If this is a know Mach issue, does anybody know a work-around or what might cause lost steps while helixing or pocketing or circling or am I looking at the computer funny and it hates me for it? Have others fixed this issue by installing a dedicated parallel port card in the PC? I've also ensured the parallel cable is away from electrical interference.

FWIW, the Tormach controller is on a UPS, no USB hubs or keys (cheap usb keyboard and mouse, wired, plugged into the front panel of the PC). I've uninstalled and reloaded Mach, acts the same. Booyah.