Massive layer shifts with MMU3
Luckily this is all the further it got before a flying bit of filament jammed the fan and halted the print.
This is the second time this has happened during a print with the MMU3. I've had plenty of successful multicolor prints in the past. I also frequently swap to using the side loader for single-filament prints; there's never been an issue with the side, but that doesn't necessarily mean the problem is the MMU.
Any idea what could be causing these occasional massive layer shifts? Last time this happened I checked to confirm that the XY shaft grub screws were still tight, so that's not it.
(Also, if this is the wrong forum section, please direct me, and sorry for being bad!)
RE: Massive layer shifts with MMU3
The most common cause for layer shifts seems to be that "avoid crossing perimeters" is active in the PrusaSlicer settings. Due to a software bug, this option is known to create "impossible" Gcode with very rapid moves and accelerations which the printer cannot follow. I would check that first.
Other potential causes are a collision of the print head with the deposited filament, e.g. due to a print partially detaching from the bed and bending upwards. I have also seen someone mention that bumps were created on the wipe tower because the print head dwelled there too long, again creating an obstacle into which the print head could bump. Do you see any signs of this in your printed objects or wipe tower?
By the look of the edges of some of those starts you have some lifting of the darker filament - either this is warping or poor adhesion - if one of these lifts into the head-path it can cause a crash and consequent problems.
So: make sure the print-sheet is clean, consider using a brim to hold the parts down and perhaps increase the bed temperature by 5°.
Cheerio,
RE: Massive layer shifts with MMU3
With my core one I need to work around two problems that have repeatedly caused serious layer shift:
- umbilical getting stuck between head and X axis motor (removal of the 90-degree Bowden bend causes the umbilical to sag a little more)
- nozzle melting into wipe tower during tool change (solution: Toolchange G code to move the head to an empty XY position)