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kyle.k5
(@kyle-k5)
Bed Skew

I'm looking for some help with possible bed skew on my Prusa Mini. I haven't had any print quality complaints so far, but today I was wrapping up on a multi-part print, and I ended up rotating one of the parts 90 degrees in relation to all of the other parts so that it would get slightly better cooling from the part fan. I believe that doing this ended up causing a fitment issue when I tried assembling the parts. Essentially I am trying to fit a square plate in a square box, and the plate does not fit in the orientation it is supposed to, but if I rotate the plate 90 degrees it does fit.

pic of bed skew

pics of skew in parts - album

This is a bed skew issue right? I have not heard of anyone experiencing this with their mini, and I believe I followed the assembly instructions correctly. (I previously built a MK2 kit with no issues, so I have a little prior assembly experience)

I found a reference to bed skew correction in the ported over marlin code for the Prusa Buddy board:  https://github.com/prusa3d/Prusa-Firmware-Buddy/blob/master/include/marlin/Configuration_A3ides_2209_MINI.h

^ search for "bed skew"

But it appears this is not exposed as a setting in the printer's GUI. Should I try to set custom gcode on each print? Would this even work in Prusa's firmware?  https://marlinfw.org/docs/gcode/M852.html

Or, do I need to re-assemble?

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Posted : 24/04/2020 11:42 am
Erl liked
bobc
 bobc
(@bobc)
Reputable Member
RE: Bed Skew

A few people have reported skew issues with Mini.

M852 appears to be disabled in the Prusa firmware. Unless you are willing to download your firmware and void warranty, the only option now is to adjust the frame.

You could post a request on the Prusa firmware repo to ask M852 to be enabled, maybe it will get implemented.

Posted : 24/04/2020 1:46 pm
kyle.k5
(@kyle-k5)
Topic starter answered:
RE: Bed Skew

I'd be really appreciative if someone could link me to any prior discussion around Prusa Mini bed skew because I cannot find it, and I'd rather not wing a fix on my own and maybe get it wrong.

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Posted : 24/04/2020 11:27 pm
Jack
 Jack
(@jack-3)
Active Member
RE: Bed Skew

I have been having an issue with bed skew as well. My prints lean forward in the Y axis. I was reading into the bed skew compensation in Marlin and I think it is essential for this design. The Mini is very sensitive to assembly and the surface it sits on.

To counter the skew I am having I have printed the Z-Bottom in the opposite orientation. My hope was that the printers own skew would print a part that corrected the printer. It helped a bit but I think Prusa needs to include skew compensation, either in the firmware or something in the slicer software.

Posted : 27/04/2020 11:03 am
bobc
 bobc
(@bobc)
Reputable Member
RE: Bed Skew

I didn't find anything directly related to Y skew, only Z skew.

I don't think there is a documented fix, but people have fixed it by adding shims, a common technique in tool shops. The Y-Z orientation all depends on the 3 screw attaching the Z bottom to the Y carriage. There is a lot to go wrong there, and not easy to adjust.

 

Posted : 27/04/2020 12:09 pm
Jack
 Jack
(@jack-3)
Active Member
RE: Bed Skew

Yes. You can shim in the z-x direction quite well. But in the z-y direction there are two bolts that more or less self centre. So the only way to adjust is to change the printed part. That’s why I tried printing the z-bottom part in the opposite orientation in the hope that it would be skew and fix the issue.

I watched a video on YouTube which explained skew compensation and I think that’s what’s needed

 

 

Posted : 27/04/2020 3:24 pm
bobc
 bobc
(@bobc)
Reputable Member
RE: Bed Skew

Well maybe the Y frame is twisted.

But if you think you need a software solution, either you need to build your own firmware or hope Prusa will implement the feature. Maybe you raised this request already? https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/385

Posted : 27/04/2020 5:30 pm
kyle.k5
(@kyle-k5)
Topic starter answered:
RE: Bed Skew

@bobcousins

Yes, that was me. I'm thinking of printing a shim to insert between the electronics housing and the Y frame.

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Posted : 27/04/2020 5:57 pm
Jack
 Jack
(@jack-3)
Active Member
RE: Bed Skew

Just an update on my "fix" by reprinting the part, I now have skew in X-Y in addition to the skew in Z-Y. I am getting very frustrated because I only print mechanical parts and they need to be dimensionally accurate. I think the only solution is a software fix as you requested on github. If they can issue a calibration print with a small excel calculator to work out the skew factor, then they could have skew factor inputs of X-Y, Z-X and Z-Y in the calibration folder on the printer. The printer is not designed to be adjusted so shimming really is a band-aid fix. Especially for beginners like who just want it to work out of the box.

Posted : 28/04/2020 10:51 am
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