Z-axis slamming bottom stop before initialization starts

My XXL has been working perfectly for over a month. Now, every time I try to initialize the machine during startup it immediately hammers the bottom stops before it does any calibrations. I’ve tried everything I can think of - even uninstalling and reinstalling CM. Any thoughts on how to make it forget everything it knows? I have checked the Z limit switch even though it never hits the switch as this happens before any of the normal initialization begins. I just need it to go back to factory defaults. Even after an uninstall/reinstall of CM, it remembers a -2.8mm setting for the Z-axis. Thanks for any suggestions.

Check the Z switch again, check to see if the little button is stuck on. I had this issue before, I was able to pull out the button and everything started working.

The switch is working perfectly - checked it multiple times. Again, this happens before it even travels upward toward the switch.

Did you open the controller box to see if the light turns on and off when you activate each one of your limit switches?

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Just checked again – all three lights are turning on and off with the appropriate switches.

Can someone check and see what your “z: Position” shows on the first screen on CM before you initialize? Thanks!

Are you Bill from Az RC Heli Canopies?

Yep, that’s me. Man, that was a long time ago! :))

Mine reads: Z: 70.400
(And 65.400 after homing cycle)

Thanks, Mike! That’s my problem - mine reads NEGATIVE 2.8 mm. The question now is how the heck can I change that if I can’t initialize the machine???

The machine positions mean nothing until you home the machine.
Are you saying when your try to home, the Z axis moves down?
Did you change anything ($$ settings perhaps?) before this happened?

Yes, that’s exactly what it does. It immediately races down as soon as it click Initialize. I have not changed any g-code settings - don’t even know how. This may have started after I accidentally ran a tool into the probe. Have done that once before with no ill-effects.

In the MDI, can you send $X to unlock the machine?
Then jog the Z axis up and down and report of that works as expected.

It doesn’t look like MDI allows anything until the machine has been initialized.

My mistake - it does allow input. Stand by…

It appears to have sent the $x. Should I try initialization now?

No, that unlocks the machine. Jog up and down.

Did you do any repairs after the probe crash? Thinking maybe your Z carriage is reversed and the belt is trying to go up when the machine is actually going down.


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Things which will reverse the Z-axis:

  • installing the Z-axis spindle carriage plate upside down
  • motor wiring being reversed/damaged
  • damaged stepper driver which only runs in that direction
  • the Z-axis homing switch being stuck closed
  • Grbl (mis)configuration

Please contact us at support@carbide3d.com and we’ll do our best to help.

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