Nozzle not touching bed when calibrating



  • Hi folks!
    After a while after giving up on trying to get my delta printer working I decided to go back and give it another fresh try.

    So the problem I am experiencing is, that when I run Auto-Calibration, the nozzle touches only first 4 perimeter points and then fails to go all the way down to the bed and a message saying "z probe was not triggered during probing move" pops up on the screen.
    Weird thing is that as the probing proceeds clockwise, it starts at 12, 2 o'clock 3 and 4 are fine but they rise as they go, you'd think that 11 o'clock would come back down as it comes close to 12, but it keeps rising.

    I tried adjusting the homed height and when I increase it, the nozzle touches first 3 point no problem, but next few points it crushes into the bed and I turn the printer off to avoid any damage. When I increase the height, it touches first few points and then floats in the air.

    As far as the endstop offsets go, I am right on money with a nozzle dead center between the 3 towers at a homed height, and it doesn't need any adjustments.
    When I move the printhead close to the bed, in the center I am about the thickness of paper away from the bed, when move it away from the center, the nozzle hovers about 0.5mm higher (dishing effect).

    following is a clip showing what is happening:
    https://drive.google.com/file/d/0B5AUUqBo3lTET3RWbXVJMHBTTEE/view?usp=sharing


  • administrators

    Increase the dive height (H parameter in the M558 command) until you have the machine calibrated. Try H20.



  • it seems just slowing down a little further away from bed when probing.
    I changed the probing points to a little closer (10mm) to the center of the bed than they were originally and it worked.

    Now I am trying to figure out how to adjust Z offset, so when the print starts, it is not diving into the bed.
    I tried adjusting Z in the M558 command, is that right? And if yes, does increasing the number will result in the nozzle further away from the bed or it will bring it closer?



  • The Z offset is done with G31 in config.g or in a macro.

    For example, I use a macro to set it, since PETG needs a different offset as compared to PLA. The PLA offset macro:
    ; PLA offset
    G31 P500 X-36 Y8 Z0.48 ; (proximity) set threshold and offsets - z offset is last one - increase to get closer to the bed
    M117 PLA Offset ; show macro being run



  • Thank you, now I ran into another problem.
    I decided NOT to run auto calibration and stick with adjusting all parameters manually because my bed is not completely level and I cannot base my calibration if everything is off by a little bit, but I still want to use mesh bed compensation.
    My printer uses FSR pressure sensors and the amount of force it takes to activate them varies with X Y coordinates, so the question is, if is there any way to compensate for the "dip" it takes to activate sensors when probing for mesh bed compensation.
    Also what gcode would I use to only adjust the printer height, or set Z0 before printing, I don't think if I should rely on repeatability of my endstops atop my XYZ towers.


  • administrators

    The way to not rely on your endstops is to run auto calibration after heating the bed and preferably also the hot end, then don't home between that and printing.

    You can correct for trigger height varying with XY position when using G32 to auto calibrate, using H parameters on the G30 commands in the bed.g file. With G29 mesh bed compensation, the only way to make corrections is to edit the bed.g file after probing.



  • Thank you dc42, running probing with bed heated will result in failure because of the FSR pressure sensors, I think their resistance changes significantly with a temperature increase, what causes nozzle to smash into the printbed.

    And as far making corrections to bed.g go, I think I will go that route.
    The center of printbed is fine, it just when it goes away from the center everything gets messed up.
    Homing repeatability is not too bad after all, it varies a tiny bit, but it is acceptable, it would be great to have live Z micro adjustment when the print starts.

    Can you think of a macro that would probe only a center of the bed and set Z 0 before every print?


  • administrators

    To set the Z height prior to printing, on a delta printer, use something like this:

    G1 X0 Y0 Z5 F6000
    G30

    On a Cartesian printer, replace X0 Y0 by the coordinates of the centre of the bed.


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