Z axis wont come down after Dev Update for G33 distortion correction

After needing the g33 command for such a time I decided to go into the Dev build since I read that wasn't implemented in prev dev, Z probe was working well before and I could manually control the Z axis to line up with the material (plywood in this case), but i cant do any of these anymore, my Z probe is at a 50.6mm offset, with a 70mm and 20mm x and y axis offset, I really need that software  distortion correction to start building my cable carrier and start doing some good woodworking.

My CNC is custom build, RAMPS 1.4 - Arduino Mega, the Z and X axis are well balanced but the Y axis has up to 3mm distortion, not including the plywood curvature (MDF Bed, 2240 x 1120 mm)

What are the steps for enabling manual Z height without or with the Z probe?, I would really like to avoid having to use the Min-Max Switches since i only do CNC Milling.

How do I properly use the G33 Command?, I had read some combinations of commands before the G33.


  • You need a calibrated z probe and normally you do
    G32 S2
    and are done if it was calibrated correctly and probing reagins set correct. Note that G33 has it's own rectangle definition for the test area configured in firmware. In your case it is important to configure Z to always correct 100% over all z positions and not remove correction over height like normally.

    Combining it with cnc is behind my personal experience, but I would expect that if it is enabled and z homed you can give material height a z=0 with G92 Z0 and it should work correct. But please test it.

    G33 L0 will show you correction matrix as a set of commands. You can use these commands to also correct the correction if you replace the Z coordinate.
  • I did a test using the Dev build and soon after G32 S2, the z axis crashed into the bed, I had been using 0.92 before this, I'm used to clicking Emergency stop and manually position the cutting bit at my 0,0,0 and then hitting all the home button's, then a G33 and that's about all I did, now with the Dev build i cant do any of that without an axis crash.

    Will G32 S2 and G33 still do their thing on 0.92? i read in a couple of places that it doesn't work in that version.
  • G33 is implemented wrong in 0.92. G32 would work under the right circumstances, which is what 1.0 improved.

    G32/G33 need real homing positions to work. If you position manually you can not tell firmware where 0,0,0 is. We have now homing flags that know you did not home so it will do real homing.

    So it essential that the printer has real endstops for homing.

    After homing xy you can use the new command in dev

    - G30 H<height> R<offset> Make probe define new Z and z offset (R) at trigger point assuming z-probe measured an object of H height.

    to set z based on a position above material. This sets z homes flag as well and also sets Z correctly. So lets say you have 20mm material and what top be 0

    G30 H20 R0

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