I am using Mach 3 version R3.043.022 with Sheetcam version 6.0.23 to run my home-built plasma cutter.  The machine randomly cuts imperfect circles, seems to kind of kick over a little bit somewhere between 1/3 and 1/2 of the way around.  When the circle completes it is not perfectly round and the end of the cut does not meet up with the beginning of the cut.  Sometimes they cut perfectly, but more often than not they are screwed up.  What could be causing this?  Straight lines work perfectly every time.  Any ideas?

Thanks,

Dale     

sounds like backslash or loosing steps.

It isn't backlash, I have checked that.  How would I tell if it is losing steps?

pretty simple

use the MDI

-put your x axis to the left end
-zerro x axis
-mark this startpoint somewhere physicaly
-take real Speed F100 (don't know in witch Units (imperial/metric) you are working)
-then G1 X? (? should be something at the right end of your machine)
-then G1X0
-then G1 X? ?(should be something at the right end of your machine)
-then G1X0

... and so on about 10-20 times
-wath your physicaly mark for X0

and then the same for y axis