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How does the auto bed leveling work, whats supposed to move?

Discussion in 'General Questions' started by robocad, Apr 16, 2016.

  1. robocad

    robocad Member

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    It does the 9 point calibration but i dont see the means by which the bed moves to level itself, or really any adjustments happening at all.
     
    #1 robocad, Apr 16, 2016
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The bed does not do the leveling, the extruder does.

    Some generic info over here:

    http://3dprintboard.com/archive/index.php/t-6178.html


    Basically it samples the bed (by using the extruder as the 'probe') and then calculates a mathematical plane that covers the entire bed with the adjustments it thinks it needs from the 9-point sample (plus the predefined Z offset you do with the M565). It then applies that correction across the points as it prints. All done in the firmware on the printer.
     
    #2 mark tomlinson, Apr 16, 2016
  3. Chuck Erwin

    Chuck Erwin Active Member

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    Auto leveling is more like auto correction/compensation.
     
    #3 Chuck Erwin, Apr 16, 2016
  4. robocad

    robocad Member

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    I still dont follow, how is the extruder being adjusted? I dont see the vertical screw rails moving any differently.
     
    #4 robocad, Apr 17, 2016
  5. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @robocad you do realise there are 3200 (200 steps x 16 divisions) microsteps for an entire single revolution of the stepper motor shaft. So it could make even larger adjustments without you 'seeing' it move.
     
    #5 WheresWaldo, Apr 17, 2016
  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    You won't

    Once it does the auto leveling dance (with the Z offset correctly defined in the startup gcode) it will automatically go to the correct height and print away. Like I said, all math. You can't see it calculating :)
     
    #6 mark tomlinson, Apr 17, 2016
  7. robocad

    robocad Member

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    No i didnt, but if the autobedleveling worked to the precision as you are describing then why am i having this problem printing a single solid sheet?

    http://imgur.com/nevn5f0

    The top corner is where it starts and prints solid but the then it starts to print the lines apart from eachother as if the bed is tilted away from the extruder.
     
    #7 robocad, Apr 17, 2016
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    #8 mark tomlinson, Apr 17, 2016
  9. robocad

    robocad Member

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    Thanks, i followed this to where the g92 code was +/- 0.2mm on all axes which vastly improved the print however there still is a spot where it thins out near the end of the print, what else can i do? Is it not possible to print a solid single layer sheet?

    http://imgur.com/vdPq4tz
     
    #9 robocad, Apr 18, 2016
  10. Geof

    Geof Volunteer Moderator
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    I shimmed my bed and used an indicator to measure flat (shims under the appropriate magnets). Then paper leveled and off to the races
     
    #10 Geof, Apr 19, 2016

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