Understanding Z-Probing

I'm trying to understand how the Z-probing works and am confused about some terminology. I've made a little diagram of a probing setup at the moment the z-probe triggers. 
In this image from what I understand, A is the Z-probe Height but I don't know what B would be called in your firmware or if it's relevant. The big one I don't understand is Max. z-probe - bed dist. Would you be able to mark on this diagram where Max. z-probe - bed dist. is?


  • Yes A is z probe height when B is the distance where it triggers. B it self is not relevant and no where entered.

    Max. z-probe - bed dist is maybe not the best name. It is just when you homed already so Z is known and you are higher the that distance when you call G32 or G33 it will go down to that distance to speed up measurement. When you start lower it will use that height instead (except on deltas where it will always home).
  • I understood Z-Probe Height to be B - A (the difference between the point where the Z-Probe triggers and when the extruder nozzle just touches the bed).

  • Yes that is correct
  • I've got one (semi-related) question...  After running G28/G32 S2 (cartesian printer - with BLTouch on a Borosilicate Glass plate), I still need to crank Z-Baby Steps to -0.40 to get prints to extrude/adhere properly [I use Aqua-Net spray]).

    What parameter (EEPROM?) should I adjust (and in which direction) will correct this?

    What am I missing here?

  • I should note that I have precisely measured my Z-Probe Height (B-A, above) to be 2.04
  • Are you already on 1.p.5dev? There was a bug with initial offset - not sure when i fixed it. Otherwise add 0.4 to z probe height then g28/g32 will start 0.4mm deeper so no extra correction required. You then compensate the error from the bug.
  • Thanks.  I'm on 1.0.4.  I'll get the 1.p.5dev and try again.  I'll post results of my testing.

  • Well, I got 1.0.5dev and I still need to "tweak" the Z-Probe Height to get my prints to adhere/print correctly.

    So, rather than 2.04, I've set it to 2.44, and everything prints as expects.

    Oh well, I can live with this...

    Thanks for your help!
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