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…