The magnetic printing plate shifted early in the print - or something else happened?

Yesterday before leaving work, I left a bunch of parts to print on our Prusa Mk4. This morning, I found all the parts with the same defect at the bottom: apparently the magnetic printing plate shifted ⅛¨ sideways on the bed 3 or 4 layers into the 7-hour print.

Unfortunately, I removed the magnetic plate without paying attention before I saw the defect, so I'm not really sure if this is what happened. It stands to reason, but it might also be both stepper motors somehow skipping at the same time. It seems unlikely, but maybe there has been a power brownout or something.

Or someone at the office interfered with the bed's movement at some point. But it seems unlikely too.

If the plate itself shifted, maybe it's because I had cleaned it with water just before and I may have left some slightly damp spots underneath, despite drying it as good as I could. I might also have failed to position the plate against the registration pins at the back of the bed, but I usually pay attention so that too is unlikely. Still, I might have been careless.

Has anybody had this sort of thing happen before? This is the first time for me.

12 comments

It could definitely be the nozzle getting caught on something so the motors skipped a few steps, I've had that happen once before and it produces this exact outcome.
- Usually only one axis skips steps, especially since the MK4 has collision detection. A shift in both axes would rather indicate a steel sheet shift imo
  
  Then they must have use some impossibly shitty magnets to be able to drag the plate sideways like that. I can literally drag my printer across the table only by the plate if I try to pull it off lengthwise instead of upwards.
  There should definitely be enough holding force to trigger the collision detection if it hits the print enough to move the plate like that.

My money is on the PETG starting to loosen and you losing tension on the belts.
You have the MK4 in an enclosure--I did too. At some point I stopped being able to print flexibles, but ASA/PCCF was still fine. Prusa support told me that the idler was getting loose and my hotend was losing grip on the fillament.
I had another print where there was a nearly 2-3cm shift in the layers between layer 5 and layer 80. Some of my belts had absolutely lost the plot. I reprinted everything in ASA or PCCF, and while upgrading to the MK4S rebuilt the printer with all ASA/PCCF parts. No problems since.
- The idler is gripping the filament just fine. I know that because I have to loosen it when I print really soft TPE and I tighten it back up and readjust the idler pressure when I print PLA or PETG - and I did that a few days ago.
  The belts might be getting loose though. I haven't checked them. They look tight but the printer has a lot of mileage, so I guess it's worth checkout out. But the re-print I just did of the same bgcode just completed fine.
  
  This could also be caused by belts being too tight, as they may cause motors to skip steps.
  Probably loose belts, but it’s important to not have them too tight. They should be snug, but you should also be able to squeeze and flex the belts without a lot of effort.

@ExtremeDullard just a guess, perhaps the extruder nozzle hit the print and offset the layers? Someone had that happen in the Orca slicer discord with a large print. It was lifting off the print bed. What filament did this happen with? Does your printer have a camera, can you watch the timelapse?
- I do have a camera but it doesn't record.
  If it was a nozzle hit, it was a violent one: this was 8 separate parts printing on the same plate and all 8 parts were similarly shifted - meaning the plate itself had shifted underneath, or both motors skipped or lost their origins. So I don't think the nozzle hit anything.
  The filament is PETG, but I don't think it matters. The prints don't lift off the bed because I use glue.
  
  @ExtremeDullard sounds like it wasn’t a nozzle impact. Curious to hear if it happens again and you get to the bottom of it. I’ve found it can be tricky to diagnose 3d printing problems because unrelated issues can cause similar print artifacts. GL!

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