Grid calibration hardware induced errors



  • After still having strange grid calibration results, I switched arms around. On the theory that if the geometry of the arms is not correct I should see it in the calibrated shape. No change, what so ever. No change if I switch one arm, or all the arms. So I am guessing that the length of my arms is pretty identical.
    So I put everything back the way it was and then rotated the effector. No change, same pattern.
    It dips deeply between the left and back column and towards the right column. In the middle it is highest.
    So that would point to the right column, yes? But in what way? I'll have to think about it.

    I rotated the Effector as well, no difference in the deformation.
    So now I have done the calibration and will print a big ring, to see if the calibration is right and my bed is THAT warped.
    I don't think it is, as I have had good first layers.



  • On my Kossel XL, the height map doesn't appear to correspond to reality and I am wondering if the IR sensor is being fooled due to differences in the amount of IR that gets returned at different locations. Two things make me think this:

    1. The height map I get shows a big single spike in the very centre of the bed. My bed consists of a slab of aluminium, a sheet of black paper and some glass. It really doesn't have a mm or so high bump in the middle. What it does have is two lines drawn on the black paper with a pencil that indicate the x and y axes. i.e. the lines cross in the middle of the bed. I am thinking that there's just enough pencil lead under the sensor when it probes the centre of the bed to give a different reading than the surrounding black paper.

    2. During my experiments I did some scans with the bed covered in blue tape. The heightmap showed the bed being more than 1mm higher than when the tape isn't there but the tape is less than 0.2mm thick.

    So, perhaps what you are seeing are differences in height being caused by variations in the amount of IR that is being reflected by your bed.

    I readily admit that I do not know the detail of how the IR sensor operates so this may all be complete nonsense.

    But have you tried rotating the bed?



  • Yes I tried rotating the bed. No real change.
    I will try covering the bed with a single sheet of white, see if that makes a difference.
    Thanks for the idea.


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