Thanks for the help, guys. Taking things from the bottom up: yes, I do have CV turned on. I've generally had good luck with it, since it smooths out all these little moves and makes them flow together better. But in this case, it seems to be a big part of the problem. When I've called G61 (exact stop) I lose a lot fewer steps, although motion is more intermittant. I upgraded to the latest bleeding-edge version of Mach, which is supposed to have improved CV, but maybe they haven't gotten to fixing combined Z-A moves yet.
I'll try turning off the toolpath in the Diagnostics page (which seems like an odd place to put that function) - thanks.
I don't have backlash turned on; the linear axes don't seem to have any, but I'm sure there's some in the rotary. However, I'm having bigger problems than that right now...
I tried fiddling with the lookahead and CV feedrate settings; nothing I did seemed to make much difference. Can someone explain what CV feedrate is, and what the effect of a "2" or ".5" instead of a "1" should be? Is the lookahead in inches, degrees, combined units or what? Wouldn't making the number bigger increase the load on the computer?
And yes, this is not the fastest or most memory-loaded computer in the world I'm running Mach on. I was under the impression that Mach didn't need a lot of CPU speed or RAM. But if that's necessary to run my long and intricate part files, I guess I can get a new one; any suggestions for something people running big files with combined moves have had good luck with?
Andrew Werby
www.computersculpture.com