Repetier Z problem

I’m having a problem with Repetier Host which is running the gcode for my MPCNC over USB. Sometimes when I start a job instead of lifting the Z-axis to the clearance plane it just goes right to work. The result is that the Z drops down AS IF it was raised to start, creating a ruined piece as it gouges out the wood.

My process is this:

  1. Line up X, Y and Z axis at 0
  2. Square the machine by measuring from sides
  3. Line up everything again at 0
  4. Press "Connect" on Repetier
  5. Load correct file
  6. Start Job
This seems to happen intermittantly, as I haven't identified when it will happen to correct it. Has anyone else experienced this? Any suggestions on how to make sure it doesn't happen? Wood is expensive! It's so frustrating to see it happen in an instant at the very beginning of the project!

Foam is cheap and forgiving. If you’re having a lot of trouble, troubleshoot with foam.

The 0,0,0 location isn’t determined by the computer, it’s determined by Marlin. Between steps 4 and 5, set the home location from the LCD or with “G92 X0 Y0 Z0”.

Does it happen after you finish one job and start a second job? But maybe doesn’t happen when you run the first job after powering Marlin?

Make sure your stepper connectors are not loose. I had the molex connectors taped together, but it wasn’t good enough - occasional loose connection caused a Z issues. On advice from the forum, I put a small zip tie around the connectors to keep them tight. That issue was cured.