What is the order of precedence for Z height?



  • When my printer is unhomed and cleared of all settings, what is the correct order to run homing, tramming, and loading the height map?

    Bed Shape

    (140, 140, 0) - perfect height at center of bed, where I home Z, and no other points on the bed are higher. this is the overall maxima
    (5, 5, -.2) - probe point one is .2mm below
    (5, 270, -.3) - probe point two is .3mm below
    (280, 135, -.25) - probe point 3 is .25mm below

    Scenario

    • my bed is level based on the tangent to the overall maxima. don't ask how, let's just assume it is
    • I run G28 to home all axes -- the printer now sees the Z height correctly for the center of the bed
    • I then run G32 to run bed tramming

    At this point:

    • What does it do with the 3 lead screw adjustments?
    • Where does the printer think Z is?
    • I'm 99.99% sure I should run the mesh probing now, right?
    • What happens if I G28 Z after it's been trammed?

    I ask because, what I think I'm observing is that the lead screw adjustments don't take into account that the bed should pivot around where the bed was Z-homed, otherwise it will throw everything off.



  • @gnydick

    I have a macro that is run, by the slicer, at the start of the print.

    That last two things the macro does are:

    • Execute G30 to set the Z=0 datum
    • Execute G29 to load the preexisting height map.

    Frederick



  • @fcwilt thanks, but not my question. I'm interested in how the controller manages the Z value based on what order you perform the different operations.


  • Moderator

    @gnydick I do home all, bed tramming (in my case two leadscrews for Z) then home Z again, though these are all in my bed tramming macro. I think it rotates the plane around X0 Y0; I just tried it and both Z screws moved the same distance, and my bed origin is in the centre, which probably means I don't actually need the second Z home. Which would explain why your home Z position is off after bed tramming, as you're probing Z at the centre, at X140 Y140.

    Ian



  • @gnydick said in What is the order of precedence for Z height?:

    @fcwilt thanks, but not my question. I'm interested in how the controller manages the Z value based on what order you perform the different operations.

    Not sure I understand. The firmware tracks any changes to the Z value regardless of the command causing the change.

    But the steps I listed insure that at the start of the print the Z value is correct, assuming your probe is configured correctly. The Z value are any other time is not terribly important.

    Frederick


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