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.
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.
The plate does indeed stick very strongly against the bed. The magnets are fine.
The most plausible explanation I have is that someone stuck their hand in the enclosure for some unexplainable reason and the bed hit their arm or something. The only problem with this theory is, there is zero reason for anybody to do that. But I did start the print early enough for a few people to still be at work when it happened.
Other than that, I’ve taken to using glue on the plate lately, because I’ve had adhesion problems. Maybe some leftover glue turned liquid-ish and degraded into some sort of lubricant with the heat (I’m printing PETG with the bed heated at 85C) and it seeped between the bed and the plate. I’ve never felt it was ever slippery though.
Or it was some leftover water that steamed over between the bed and the plate and lifted the plate for a second, air-hockey stylee.
None of this seems very likely though. So I cleaned the bed and the plate real thoroughly, installed the plate tight against the registration pins, upgraded the firmware to the latest for good measure, slathered glue super-carefully all over the plate, making sure it didn’t go overboard, and started the same print once more. I’m watching it remotely through the webcam I installed in the enclosure and it seems to be going fine.
Belts look tight, but a good inspection of them and their pulleys might tell you something.
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.
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