CNC random Z plane change

Running a fairly simple file just cutting a pocket in Maple and suddenly the machine just digs down into the wood and through the wasteboard.

What may have caused this random change? It’s not in the preview of the file I made at all.

I have run into this in the past, and found the set screw was loose on the gear attached to the stepper motor. I tightened it, and added some locktite. No more issues with that. Hope this helps

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I’ll double check the screws. Just seemed random and went right through everything.

This may be caused by a number of different things:

  • a disconnect in how the origin is set in the file and how the zero is set relative to the stock, see: and
    • if using the Probe this may be caused by setting the Probe as for an X/Y/Z probe at a corner, but probing for Z only, see: (the Probe should be fully on the surface, rather than only the body on the stock and the 3mm lip off the stock)
    • if using the BitSetter, changing a tool without using the Change Tool button can result in too deep or too high cutting
  • setting the Z-axis safety/retract height in the CAM program (Job Setup | Machine | Retract Height in Carbide Create) to a value greater than is available above where the machine expects the top of the stock to be, resulting in the machine bottoming out against the top stock, thinking it is too high, then plunging down too far in an effort to travel down as far as that failed effort would allow. Setting the origin to the bottom of the stock/wasteboard surface, while setting the zero to the top of the stock may also cause this problem
  • a mechanical difficulty — check pulley set screws, Z-axis belt tension (if using a belt drive)
  • Grbl misconfiguration — check that you have the correct Z-axis enabled, in particular, having a Z-Plus, but configuring for an HDZ will cause overtravel in the Z-axis
  • an electronics issue — check the wiring and connectors
  • the endmill gradually working loose — check that an adequate length of shaft is in the collet and tighten using two wrenches per the instructions

What z axis do you have?

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