MK3S+ and MMU3 Print head hitting wipe tower during purge and causing offsets in print (Photos attached)
I added the MMU3 a little after it came out to my stock purchased MK3S+ printer purchased from PRUSA a few years ago. I have enjoyed quite a bit of error free printing with the MK3S+ since receiving it and working out a few issues regarding cylinder printing. I had to turn off crash detection because cylindrical object prints were having crashes during the print. They were observable as in there was nothing in the way but the controller decided there was an impact and homed the print head then returned sometimes without issue, sometimes with a slight layer offset. The point of that was to say that crash detection has been off for nearly the entire time I have owned the printer as suggested by PRUSA support.
I built and installed the MMU3 when I received it. I had some very early filament change issues that (likely due to dumb luck making adjustments) I worked out and its been fairly flawless. I did have one change that occurred much later where that little wisp of filament at the end of the point broke off and caused a jam but nothing since then. I had not done a lot of complex MMU prints but was pleasantly surprised with the success using the MMU3 after reading the horror stories around MMU2.
The day after setting up the MMU3 I had a friend ask if I could print something that happened to be multicolor which I fount fortuitous and something to test on. Its not terribly large ~4 hour print with color changes very near the end of the print that are small volumes. There are 2 color changes at the start that never cause issues. The wipe tower prints very neatly the entire time but near the end when the color changes happen at the top the purge seems to be come out in blobs that cause the print head to bump them and the head gets offset. I was only ever able to print it correctly once. Another friend liked it and asked for his own and I was never able to reproduce. Its been a year and an entire new hotend later so I thought I would try again. I ran it last night and when I woke up in the early morning I saw it had gotten so offset that the wipe tower was printing over top of the print itself. The model is called "Duck You", to explain what the photos are intended to be.
I have no idea what to do at this point, when I use the filaments individually no such issues but in the MMU with the wipe tower I see this repeatedly. I have probably wasted 1/2 a spool trying to reprint this one thing between last summer and this one. New spools were used this time around as well. All Prusament PETG.
Any thoughts or suggestions? I would rather print this in one shot rather than break it up etc... the MMU3 should work properly.
RE: MK3S+ and MMU3 Print head hitting wipe tower during purge and causing offsets in print (Photos attached)
Try moving it. I had a bit of trouble with my wipe tower at the top right of the printer. It would always let loose a little and would drag. I wondered if maybe that are wasn't heating properly and moved the tower left of the model and it works perfectly for me now
RE: MK3S+ and MMU3 Print head hitting wipe tower during purge and causing offsets in print (Photos attached)
What @Xayoz said. I too noticed more issues with colour changes when I had the wipe tower positioned at the sides of the build plate. Since then I always try to position it in the middle. Usually right at the front or at the back. I think it could have something to do with the PTFE tube leading from the MMU3 to the Extruder having a weird angle or something, though I can’t really believe that myself.
I since then also changed a lot of things on my setup so I don’t even know if the position of the wipe tower makes any difference.
RE: MK3S+ and MMU3 Print head hitting wipe tower during purge and causing offsets in print (Photos attached)
I had this issue with the MK4 and mmu3. It messed up about 6 prints 2 to 3 days in of a 4 day print with 2300+ filament changes. I found that the input shaping was just too fast and you could hear the nozzel hitting a blob at the top of the wipe tower. I slowed all the speeds down to 40 and was able to finish the print. I also tightened up the x and y axis belts. One of my other problems was that the print was slightly skinny, and it was probably wiggly when it got halfway up. Organic supports fixed that but your print looks like it has a stable base.