Large H-Bot print out of dimensios.

  • I have a tricky problem. The printer is around 800x800x800 mm H-Bot with new Duet ethernet 1.02 and 1.21 firmware. XY axes move horizontally and bed descends down in a standard fashion. The frame is from 80x80 alu profiles stiff enough, the X axis slides on 4 HIWIN carriages, wide enough to avoid skewing.

    Two large models of height 500 and 800 mm were printed (30 - 100 hours) and the dimensions and angles are perfect at the bottom (first layers) but they are off by 4 - 6mm at the top of the object.
    This is not due to any kind of plastic warping but head movement itself.
    One of the prints was halted, powered off and manually resurrected after two weeks. The head was moving perfectly on the off dimensioned path.
    During the print the machine was homed many times.

    Mesh leveling was used in second case with taper off set at 5mm in config.

    And what is curious, the print of a simple (vase without bottom) 50 hours cube with circle inside has perfect dimensions.

    We have many smaller cartesian machines 600x500x500 and they never produced such dimension errors.

    Because we use the machine on a daily basis and have some more technical stuff to print now, I'm considering changing it to cartesian.

    Do you have any clue what can be the source of this problem?

  • When you say dimensions are off by 4-6 mm, what exactly does that mean? Are they too tall or short, or is the error in the XY plane?

    Is the top of the object much larger than the bottom in the XY dimensions?

    Were the prints made at the center of the bed? Is the top of the object centered also?

  • The printed object is 4-6 mm smaller in X direction, Y was not measured because it's hard to measure properly and Z is just fine.
    Bottom layers of the print are ok. and the top is too narrow, it looks like the print is tapered linearly from bottom to the top. There are no jumps, no missed steps, no other visible artifacts or deformation.

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