Question about auto cal of delta using bed.g



  • Hi,

    When the auto-cal process finishes it reports deviation before and after.

    On my printer the before deviation of a 2nd (or 3rd, 4th, etc) run never seems to match the after deviation of the previous run.

    Why? Does it tell me anything important about my printer?

    My deviations are not very good (after was 0.065) and I cannot determine what to do to improve things.

    I've read (over and over) the notes about calibrating a delta and have tried my best to set things to right but nothing seems to improving my cal results.

    Thanks.

    Frederick



  • What probe are you using for calibration?


  • administrators

    What it's telling you is that your printer build has geometrical errors that auto calibration can't compensate for, or that your Z probe doesn't have a consistent trigger height. See https://duet3d.com/wiki/Calibrating_a_delta_printer. Putting a bulls eye spirit level on the effector is a good start because it shows up many types of error.



  • @Jackal:

    What probe are you using for calibration?

    dc42's IR device.

    Frederick



  • @dc42:

    What it's telling you is that your printer build has geometrical errors that auto calibration can't compensate for, or that your Z probe doesn't have a consistent trigger height. See https://duet3d.com/wiki/Calibrating_a_delta_printer. Putting a bulls eye spirit level on the effector is a good start because it shows up many types of error.

    I have read that many times.

    In the past few days I took the printer apart, replaced the plastic corners with metal ones, tried to keep the frame plumb, level and square as appropriate, replaced the stock arms with some well know carbon fiber with magnetic balls units, installed your IR sensor - in short I did my best to do it right - but it seems to have still come out wrong.

    I will try the spirit level and see what I can learn from that.

    Thanks.

    Frederick


  • administrators

    What bed surface are you using?



  • @dc42:

    What bed surface are you using?

    It's a 1/2" piece of MDF supporting a 3mm aluminum heater with a 3mm piece of borosilicate glass on top.

    I didn't think I should mount the aluminum heater directly to the metal frame thus the piece of MDF.

    I used an adjustable square to see if the towers were perpendicular to the surface of the glass - it seemed good from all three towers but I don't know exactly how accurate it must be.

    Laying the edge of the steel ruler across the glass doesn't reveal any obvious problems with the glass not being flat - but again I don't know how flat it must be - or even how to accurately to measure for that.

    Thanks.

    Frederick


  • administrators

    Do you have black paper between the glass and the aluminium? Reflections from below the glass can cause the IR sensor to have a trigger height that varies with position.



  • @dc42:

    Do you have black paper between the glass and the aluminium? Reflections from below the glass can cause the IR sensor to have a trigger height that varies with position.

    No - I was not aware of that practice - I will give it a try.

    Thanks.

    Frederick


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