Greetings, I'm new to Mach3 and have been wrestling with an issue on a 3 axis mill:

  I'm cutting a cam out of polymer, the program is a simple contour consisting of three depth cuts followed by a finishing pass.  Sometimes it works perfect.  Other times the coordinates seem to shift ~1/2" in the X and Y axes when doing the rapid movement between depth cuts.  After completing the contour at a certain depth I see the spindle retract above the work, rapid move to the correct position to start the next depth cut, pause for a split second, then rapid move again laterally roughly the same distance it just moved before starting the contour again, but this time the path is clearly off of what it should be.  I've found that it usually can be fixed by resetting the program, hitting 'Ref All Home,' rewinding the G-code and running the program again.  I'm at a loss as to why I can run the same code without changes but have different results.  My solution is also very time consuming so I'd like to see if it's possible to sort out a 'real' fix.

  Running Mach3 on an Lenovo Thinkcentre, mill is an X4-800 desktop engraving machine, G-code posted from MasterCam X8.  All thoughts and ideas welcome and appreciated!

Try reducing your Velocity and Acceleration by 50% for both the X and Y axes in Motor Tuning (saving the changes after each change).

If this resolves the problem then fine tune your motor settings for best performance consistent with reliable operation.

Tweakie.

Much appreciated, Tweakie.  My acceleration was pretty low on the motors and I played around with the motor tuning quite a bit, at some point I bumped the USB-B cable going into the control unit and the machine started working fine.  Literally a loose cable that got jostled when the machine had a rapid movement.  Got the cable tightened up and working on isolating the control box from the CNC, looks like the issue is resolved....

:: face palm ::