Configuring Bed Leveling

  • I finally got around to install dc42's IR probe. I've calibrated it according to the instructions here:
    After that I used G29 to run Mesh probing and then i tried to print. I could hear that the Z-axis always keeps adjusting but the first layer comes out pretty bad.
    I purposely made the bed very un-flat. The nozzle does not crash into the bed as it should, but the it is to high for a proper first layer.I don't really understand what the Z offset in the G31 command does nor what the calibration is doing.

    What could be the issue here?

  • @CoolM8:

    …...........................I don't really understand what the Z offset in the G31 command does .....................

    OK so when you first fire up the printer, the axes could be anywhere, that is why we do homing to set the axis to a reference point. Sorry if that sounds patronising but bear with me. Now for X and Y it's easy enough to do. Just fit a switch at the extreme of movement and when the switch gets triggered, we know exactly where the print head is for that axis. So we can now move to any point with respect to that starting (reference) point.

    We could do the same for the Z axis but the trouble is, we would need the switch to trigger at the exact point where the nozzle is just touching the bed. That becomes very tedious to set up and could also move over time. Also, if we get it slightly wrong, the nozzle crashes into the bed before the switch triggers (not good). So what we do is still have a switch (but we sometimes call it a probe), but arrange it so that it triggers slightly before the nozzle touches the bed. Then we "tell" the electronics that the point where the nozzle just touches the bed is n.nnn millimetres after the switch triggers. The "n.nnn" is the Z offset. So once the switch has triggered, if we then want to get to the point where the nozzle is just touching the bed (Z=0), the printer will need to move by the Z offset. If you get the Z offset wrong, the printer doesn't "know" any better so it will assume that Z=0 is whatever you have told it is the distance (the Z offset) from point where it "sees" the trigger.



  • Ok i get that, and that's why the calibration sets Z=0 when the nozzle touches the bed. Then i have to move the bed 5mm down and call G30 S-1, but it seem the result i get is not correct. Or did i read this wrong?:

    Raise the head 5mm and remove the paper. Then send command G30 S-1 to probe the bed at that point without adjusting the Z height setting

  • Hmm, now it works. Somehow it didn't use the correct the changed offset.


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