Layer shifts after installing MMU3
I recently installed the MMU3 to my MK3s+, and have had layer shifts like I have never seen before, stairstepping clear across the build plate, and occasionally back again. I've checked the belts, pullies, even done voltage verifications for the steppers. If I print in single color, or remove the MMU, I don't have the issues. I've checked the bed manually to make sure it's level and true, cleaned the rods and lubricated the bearings (since I had to do some disassembly to install the MMU, I just went and did some heavy maintenance while I was at it). I have it on a nice heavy table, so it's not shaking itself to shifts, and I've not seen any obstructions to cause any jumps or collisions, though I've always had issues with the Y axis crashing endlessly until I turned off crash detection. (Perhaps the issue is related?)
To those with more experience with troubleshooting such issues, is there something that I have overlooked mechanically? Maybe some test I can run to help diagnose this problem, or other issues down the road? I can toss the files up, just to see if the issue is how it's sliced (as I am suspecting that it might be), if someone wants them!
(I'm trying to print an anatomical heart as a teaching prop for my cardiac class, though you probably can't tell from the mess in the pictures)
Here is the anatomical heart model I went with, since it supports MMU and looks great
I'm using Overture PLA and PLA+ for all my filaments, as they have been the most consistent for me. First layer at 220c, subsequent at 214c. . 
RE: Layer shifts after installing MMU3
I am having this issue as well. I am on a MK4 MMU3.
RE: Layer shifts after installing MMU3
I am facing a similar issue with a MK4 and MMU3, the wipe tower gets a blob of hardened filament on it, then the nozzle hits it causing the layers to shift and ruins the print.
RE: Layer shifts after installing MMU3
Got same issue with petg, when the tower as some blob inside, this cause the noozle to hit it and can cause some issue in long printing
RE: Layer shifts after installing MMU3
I dissasembled my MMU3 on myMK3S because of this... I only was able to print a 2 color sheep, and any other print that has a few color changes has failed on me. After a few swaps, the purge block keeps getting blobs, on which the print head blocks and layer shifts occur.
I was excited for the MMU3 when I ordered it. First test print went fine (the sheep), after that, nothing but misery. So I gave up... Maybe I'll try again when Prusa finally acknowledges this issue, as this is something I find back a lot on the internet, without any real solutions.
I was thinking of upgrading the MK3S+ to an MK3.5, but seeing that this upgrade costs almost as much as a Bambu lab A1 with AMS Lite... I'm not so sure.
If you ever figure out how to solve it... 🙂 I'll do the same.
RE: Layer shifts after installing MMU3
I have the same with MK4 MMU3.My first print with MMU3 was the sheep with 3 colors. Worked wonderfully.
The printing with the hedgehog went wrong twice.Always at the same place. The 2nd attempt was re-sliced. When I printed it, it sounded like it was hitting somewhere
The print is colored single model
RE: Layer shifts after installing MMU3
For me it was due to the temperature I had set PLA to 240 and something was probably dripping, getting hard, and then it jammed and the layers shifted.... look at the cleaning tower to see if there are any bloobs...
RE: Layer shifts after installing MMU3
Sounds like too much difference in temperature between filaments can cause this. I'm my case 195 / 225.
I will reduce that difference and try again.
RE: Layer shifts after installing MMU3
I was able to fix this by running the belt tuner app again. After some time belts can strech and loose some tension. My had loosen so after adjusting the belt tension I have had no more issues. Well, once but not consistent like before. Feliz Printing.
RE: Layer shifts after installing MMU3
Support mentioned lowering nozzle temps to remove the blob. I haven't had time to check if that helps as I disabled the MMU3 so I could get some prints out using single filaments.
Never thought I would say this but the Bambu AMS is a much better solution than this weird cassette buffer setup that is a pain to load. Checked the settings for my Bambu at it actually prints hotter than my Prusa's with none of the blobs.
RE: Layer shifts after installing MMU3
I have the same problem - MK4 + MMU3. I've been solving one print for a week now and still the same result, only always with a different shift in a different layer. approximately 0.5 kg of material thrown away 🙄.
I also tried downgrading the firmware to version 6.0.0, but that didn't help.
Full size:
Mini version too:
RE: Layer shifts after installing MMU3
I ended up solving my blob issues with two tweaks.
1. Changed the Wipe tower purge line spacing to 300%, this fixed a lot of the blob formation problem but still had some random issues.
2. Tuned the filament settings for my specific brand of PLA, luckily I found presets that have worked perfectly for me.
RE: Layer shifts after installing MMU3
I just completed my MMU3 upgrade this week. Upgraded machine the other week after installing it while waiting on MMU parts.
I had no layer shifts at all before the upgrade and I printed all my MMU3 parts and lots of others.
Machine is at firmware 6.1.2+7894
I had my first experience of the layer shift and it happened 2-3 layers into the job. It shifted left in my case.
Being a Ex-tech specialist I will dig in and see if I can replicate (1st order to fixing it).
RE: Layer shifts after installing MMU3
I have the same problem. I am having y-axis shifts. I spent over 20 hours with the help desk and they kept insisting that the MMU3 with my MK4 had no relationship to the y-axis shift. I even proved it by removing the MMU3 and had a number of perfect builds. I took all the steps of making sure the belt was tuned, no interference and all the other recommended steps. I did it with and without a wipe tower. So far nothing has worked. I also have the blob problem. Also having problems with filament getting stuck in the feeder tube. I suspect the temperature seems a bit too high. I am thinking of disconnecting the MMU3 until these problems are fixed.
RE: Layer shifts after installing MMU3
I am having the same issue. I posted it as an answer on a different thread, but in my case, the wipe tower has nothing to do with it, as I am currently trying to print a single color print. As someone else stated, it appears to only happen with full-bed prints, compared to small prints. Very frustrating.
RE: Layer shifts after installing MMU3
In the mean time, I upgraded my MK4 to MK4s and reinstalled my MMu3.
in the beginning, same issue, but then I found a post somewhere to basically remove all profiles (printer and filament) and only use generic ones or specific (prusa tuned) ones. Since then, I have had numerous succesfull 5 color prints!
I basically removed prusaslicer (completely), reinstalled it imported all profiles I needed.
The only issue I have now, is that I don’t use the filament buffer due to lack of space and I use self rewinding spool holders. They work fine for the most part but when the spool is full it sometimes starts winding up NEXT to the spool. I am going to design some guides to guide it better and that should solve the problem.
so, now I am happy!
Good luck to everyone having issues.