Core One / MMU3 Issues unloading filament (works fine loading it)  

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

it happens to me (ABS) when it's standing for hours e.g. after some failure, then trying to remove the filament which got stuck in the printhead in the meantime.

My core one sometimes thinks it's out of filament at the printhead, which seems to be caused by vibrations.

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

Yeah, I just check the MMU3 by opening it up and looking. No crap in there that I can see and all of the functions appear to be working properly. I'd call Prusa support, but that were less than helpful last time.

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

I had a similar problem with mine - have you checked the length of the ptfe tube between the mmu and the nextruder? You need to ensure the setting in the printer matches the length exactly. Too short or too long by a few mm and you'll get the symptoms you describe.

RE:

For the failure mode I described, the filament will be physically stuck in the extruder and require a fair amount of force to pull out. A tube length mismatch would probably look different (filament not stuck in extruder). 

For debugging, make sure the "preload filament" function works reliably (MMU cycles through all sources). This needs to run like clockwork or there is no chance a print with hundreds of tool changes will complete.

For test prints to exercise MMU changes within the same material, you can dial down the purge volume so the wipe tower gets smaller (saves a few grams of filament but most importantly, time)

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

that’s what the filament looks like when it’s retracted from the extruder…

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

Another thing that happened yesterday is that the filament got stuck around the extruder gear and had to be manually removed.

The MMU3 seems to be a haphazard solution.

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

Hello,

I had a lot of problems with Core One + MMu2S upgraded to 3. The most of thse was solved redoing the filament calibration. In fact, each time to set the nextruder tension screews, you open the nextruder, my advice is reset le calibration data to reset the point exactly between the coordination between the motor of the nextruder and the motor of the mmu3 to load of unload filaments. The moment when the magnet of the idler nut gives the info to the sensor is crucial to a good load un unload. For my part, I had to print a shorter swivel to break the circuit at the right moment when the filament touch the nextruder PG ring.

Cheers

RE: Core One / MMU3 Issues unloading filament (works fine loading it)

I guess the problem relates also to this thread (not solved -- at least for me):

https://forum.prusa3d.com/forum/prusa-core-one-hardware-firmware-and-software-help/core-one-mmu3-filament-unloading-getting-stuck/