Kossel Mini skewing prints even with autocalbration on. Help?

  • I work in a library that's hoping to use this Kossel Mini kit to print jobs for students and it was recently upgraded to a Duet 0.6 so that we can use autocalibration and the Duet Web Control to use it. However, we've noticed a lot of our prints are coming out heavily skewed in the direction facing the x-tower(cubes into rhombuses, etc) I've checked that the autocalibration routine is consistently getting converging results and been able to get slightly more square prints by manually tweaking the endstop offsets in my config files.

    We really want to be able to rely on autocalibration in such a heavy use environment. Can anybody advise on this?

  • How many factors are you using when autoncalibrating? Have you measured the rod length?

  • I'm using the 7-factor autocalibration routine and I have measured the rod length and it is correct. This is actually my first time calibrating a delta printer.

    Also, when I print a 20mm cube, it gets skewed so that the dimensions become (20.88, 20.0, 20.0), essentially. Is it possible my endstop offsets are wrong?

  • administrators

    That type of distortion is caused by a geometrical error in the printer. See https://duet3d.com/wiki/Calibrating_a_delta_printer#Make_sure_your_build_is_accurate for common causes.

  • I was playing with some experimental carriage designs recently, and was getting the skewed prints as well. In my case it was the carriage face wasn't parallel with the face of the towers. (So, if you were looking straight down at a tower, the front face of the tower towards the bed wasn't parallel with the front plane of the carriage facing towards the bed). This created the kind of skew you're referring to.

  • I was able to fix the distortion! Playing around with M556 command values was able to get me really close. But, just when I had finished getting a value that got me really close I noticed the diagonal rod connections to the effector had popped closer together due to what appeared to be a really strong spring tensioner that was installed on the diagonal rods to make them stiffer.

    After I popped them back into place and got rid of the tensioner, everything went perfectly and I ended up not needing the M556 command. Thanks for all the help everyone!

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