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Solved Z offset suddenly changes

Discussion in 'Troubleshooting' started by Bd182, Jul 8, 2020.

  1. Bd182

    Bd182 Member

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    I've been printing for a year with Z offset of 0.3mm. Suddenly I was dragging the head on the glass, and I had to set Z offset to 1.0. A week later I was no longer adhering to the bed, and I had to change the Z offset to 0.5. Today I'm back to 1.0. What's going on?
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Something is loose/changing.
    Check the carriage/bolts where the extruder mounts and check the Z nuts (one on each side up under the crossbar if you are on an R1/R1+ -- you didn't say which model). They might have gotten out of position. This video covers that :

     
  3. Bd182

    Bd182 Member

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    Thanks Mark-

    I see no play in the carriage bolts and the carriage is level to within 1/8". If I wiggle the bed up and down at the front edge, it seems to move more than I remember, but, who knows? The Y axis guide rods seem to have a lot of play in the bearing blocks. Is that normal?

    But, I just noticed that I had dropped one of the conductors off the left switch on the R1+. I will see if things return to stable. The Zoffset is now 0.45.
     
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, if a wire falls off of of a Z switch you will loose half of the functionality :)

    It will still work, but you run the risk that half of the bed is not correctly sensed
     
    #4 mark tomlinson, Jul 8, 2020
    Last edited: Jul 8, 2020
  5. Bd182

    Bd182 Member

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    I found the auto leveling procedure tedious and disabled it last year. I have seen no disadvantage in that, and for months all my prints have had equal elevation at all points (though I never print anything as big as the whole bed). Even with the recent failure, the depth error was equal on left and right sides. And, when I get the right Z offset, the prints are fine. I did re-enable G29 when I began having trouble, but it made no difference, and I've disabled it again.
     
  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Manual leveling is always superior to the v1.x Marlin Auto Bed Leveling.
    THe later versions (v2.x) with UBL and Mesh are potentially better if your bed is warped, but you can just put a thin sheet of float glass over the bed and solve that :)
     
  7. Bd182

    Bd182 Member

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    Good to know that I'm not operating off the reservation. And, I added a sheet of float glass last year too after my fancy-pants "hard glass" fractured when printing PLA on bare glass. I guess I don't understand why they use the expensive glass when I have found window glass to be just as good, even better.

    So far my Z axis is stable. I may have had an intermittent contact on the left side limit switch as the connector worked itself loose. Thanks for being here and pointing me in the right direction.
     
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    They used borosilicate (aka Pyrex) because it can handle extreme thermal transitions better than other types of glass.
    The problems are:

    1) The temperatures and rate of change for those temperatures on a Robo are nowhere near extreme.
    2) it is more expensive
    3) it is harder to get flat
    4) it tends to chip or flake

    Float glass is fine given the range of temperatures the Robo uses and the speed at which it will change them.
     

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