Setting Z-Offset and values seem to keep climbing.

  • I'm following the betrue3d Duet/BLTouch guide, specificly the "Find Z-offset:" section.

    I start from step 3 as everything above that step is working as expected.

    Almost every time I do a measurement cycle:

    G1 Z10
    G30 S-1

    The distance number reported back seems to increase:


    I'm at a loss as to what could cause this other than something on the Z Axis is loose, but I've checked everything, many times. Could be missed steps but I think that is unlikely from my testing.

    Anyone have a clue?


  • administrators

    One possibility is that you are probing too fast. When the Z probe triggers, RRF stops the Z axis abruptly. If it can't stop fast enough then it will overshoot and skip Z motor steps. Then the Z axis is lower than RRF thinks it is, so the next G30 triggers early and RRF interprets this as a higher trigger height. So try reducing the probing speed (M558 F parameter) and see whether that gives more consistent results.

    Another possibility is that the BLTouch is heating up and its trigger height is changing; or that something else is heating up and the height of the print head above the bed really is changing. But that's not likely unless you are running this test while the hot end or bed is heating up.

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