Layer shifting when using MMU, please help
So this issue has been kicking my butt the last few days, wanted to see if anyone might be able to help. Printer is a MK3S+ stock with MMU3 attached, prusaslicer the most recent 2.9 one. On this print I’ve been trying to do, it seems like every time I try to print it out, there’s a layer shift on the x-axis:
I pretty much ran through everything in the layer shift guide ( https://help.prusa3d.com/article/layer-shifting_2020) to no avail; adjusted the tension to optimal on all belts (even if only the x axis was off, and even then the belt test said it was within normal range whereas the tuner app disagreed, so I tightened it more to satisfy it even though the belt test now says x is potentially too tight), the pulley is tight and not loose and installed correctly with at least 1 of the grub screws on the flat part of the motor, MMU3 isn’t on stealth mode (which I didn’t even realize it was), etc etc. Tried different filaments, things very marginally improved with each attempt but there was still a noticeable layer shift.
Fed up, I finally just decided to try a mono color print instead (still running through the MMU), and lo and behold, it printed fine:
Compared with another failed one:
So something has to be up with my MMU3 that’s causing this layer shift. It’s not tied to a specific filament slot, slot 4 is what the gold pla is loaded into, slot 2 is silver, and slot 5 is black, and as you can see from the intial photos it shifted using black and silver to fill in the dot. But I’m at a loss as to what to try now to fix it since that one guide doesn’t cover any issues regarding an MMU is apparently causing this.
MMU layout for reference, 4 of the filament slots are in soval dry boxes and I can’t say I’ve noticed any issues with filament feeding or going into the buffer:
Does anyone have some suggestions or advice on how I can fix this so my nightmare can finally be over? I’m at a loss as to why the layer shift issues only pop up when I actually use the MMU to change colors like its intended use. I will say I haven’t always had this problem, it’s only been an issue now and not before, seemed to work fine before outside of rather meh overhangs sometimes.
Thanks!
RE: Layer shifting when using MMU, please help
Hi!
When my MMU3 was attached to my MK3S+, I never had this issue. I've since upgraded it to an MK3.9S, which has brought new challenges, but that's for another time.
My two thoughts on your issue are 1) have you tried to see what you get when you feed not from the drier boxes but just from the spool holders, and 2) have you tried using different slots for at least two of the colors (i.e. 1, 3 and something else).
What I'm thinking is that you might have something in the filament path (drier box, buffer assembly) that is binding EVER SO SLIGHTLY, but just enough to cause your issue.
Just a thought.
RE: Layer shifting when using MMU, please help
Gave it a shot, loaded the silver into the roller for #1, same result unfortunately.
I did notice that the firmware for the printer and MMU were like 1 update behind when I checked, so gonna try flashing it in and trying again. And if that don’t work…well it is really tempting to pitch it against a wall at that point…
RE: Layer shifting when using MMU, please help
Can anyone help??? Updated all the firmware, hell I unloaded, disconnected all the tubes, reconnected them, reloaded, still the same. This is so stupid 😑
RE: Layer shifting when using MMU, please help
Thanks for no help at all.
RE: Layer shifting when using MMU, please help
Sorry the feedback has been limited - I suspect people just have no ideas. You said you went through the layer shift debugging already, and I would bet most people can't see how the MMU3 would contribute to layer shifting. The only way I can see it is if it drops blobs on the print which the print head hits and skips.
I'm a new MMU3 user (on a MK4, about to upgrade to MK4S) and so far almost every issue has been related to the presets I was using not being fully based on the MMU3 default presets. I kept trying to load .3mf saved files which were sliced with the non-MMU3 presets, and it just wasn't working. Have you tried just using default profiles for all 3 (print settings, filament, printer)?
Prusa MK4 since Jan 2024, Printables: @MikeB_1505898
RE: Layer shifting when using MMU, please help
As Mike B. said, it's not a "no help at all" situation, it's that folks are kind of stumped.
If you have verified that there is no resistance in the filament paths, if you are using the proper machine type and filament specs. for slices, clean nozzle and proper belt tension, then I'm sorry but I've got nothing.
RE: Layer shifting when using MMU, please help
not sure if you solved this but i ran into this today as well, first use of my mmu 3. my problem was the mmu profiles have pla temps very low, was making the wipe tower rough and the nozzle woulds hit it a lot. set my temps back to normal and no problem with that since.
RE: Layer shifting when using MMU, please help
Nope still not fixed, and if it weren’t for tariffs I would’ve bought the new Bambu and ams by now…
Anyways what are your temps at? I’ve always used the default pla (215/205) generic profile ones and it had been printing fine until whatever borked up the machine.
Other more recent things I’ve tried are trying every version of the firmware for the MMU3/MK3S+ combo and nothing works (the only weird difference is older versions would cause the shift to go to the right, while newer ones make it go to the left). Partially disassembled the damn thing looking for any sort of clogs, loose gears or filament on the mmu3, nothing. Re-lubed all the rods and calibrated belt tension again on the MK3S, nothing. Like fuck, I’m not sure dissembling everything at this point would make a difference, and I highly doubt it would since just using 1 extruder or filament only, it works fine. But for whatever fucking reason, introducing color change with the MMU3 just fucks everything to hell.
not sure if you solved this but i ran into this today as well, first use of my mmu 3. my problem was the mmu profiles have pla temps very low, was making the wipe tower rough and the nozzle woulds hit it a lot. set my temps back to normal and no problem with that since.