Still failing to print  

Re: Still failing to print

Found the culprit.

I watched this come down when it was trying to print some black, as a result it got caught before the gears in the extruder body. 🙁

Re: Still failing to print

Found the culprit.

Printing PETG with wrong settings and this is a result. I had the same experience with MKG PETG at 255C. Over time (~50 tool changes) you will get a blob of strings. I still haven't found a nice setting to prevent this long and sturdy PETG hairs. So if you really want to print PETG with MMU, you need to clean up this mess and monitor the print until we found the correct way to print PETG.

Re: Still failing to print

Maybe the clogging for stringy materials could be fixed with an improved filament cutter in the selector and the ability to instruct the MMU to always trim the ends of filaments before loading it to the extruder. Or extruding to the waste tower while rapidly cooling the hotend down by 20-30 degrees before each filament unload to minimize stringing.

I'm waiting for new bowden tubes for mine before I attempt more multicolor prints. All the PLA I have seems to be too low quality for the MMU and ends up grinding down and getting stuck before it ever reaches the extruder gears.

If nothing else, I'm sure the problems will be worked out eventually and I'll just leave it on the printer in the mean time, it doesn't seem to interfere with my single color prints.

Re: Still failing to print

Maybe the clogging for stringy materials could be fixed with an improved filament cutter in the selector and the ability to instruct the MMU to always trim the ends of filaments before loading it to the extruder. Or extruding to the waste tower while rapidly cooling the hotend down by 20-30 degrees before each filament unload to minimize stringing.

I'm waiting for new bowden tubes for mine before I attempt more multicolor prints. All the PLA I have seems to be too low quality for the MMU and ends up grinding down and getting stuck before it ever reaches the extruder gears.

Filament cutter: It's not practical for different reason. The strings can get very long as you can see on the images. You have to remove it completely from the bowden tube in order to make a clean cut. The MMU would require a heavy maintenance if it would cut every time. (roughly 800 cuts every 24 hours print time is a lot). I don't see a benefit to do it all the time as it's not a solution for all the possible filament issues.

Filament Quality: So far I was able to use any PLA for MMU. Grinding down is a result of thick tip (get's stuck somewhere) and wrong unloading settings. Thick tip is a result of wrong print temp and unloading/cooling settings. Both things can be managed in Slic3r. I'm not sure why people are replacing the bowden tube.

Re: Still failing to print

A string "blob" like that one is caused by 2 things:

Insufficient ramming.
Slow initial unload. (there are also a few causes of this 🙁 )

The string does not detach from the filament tip and a very fine string is drawn from the melt zone up to the MMU. The next filament load pushes the string back down into the extruder where it can either jam the filament or melt. If it jams the filament, it also causes the filament to be ground down by the drive pulley (either MMU or Bondtech), which also causes a load failure later in the print (or on the next print 😉 )

Peter

Re: Still failing to print

"Slow initial unload"

ive only had this kinda thing as the cause of stringing.

Re: Still failing to print

Thanks for all the feed back, what are some settings that people have had success with for ramming?
Unload speed at start I have set to 120mm/s
I have increased cooling moves to 4 to see how this goes.

What about ramming settings? Prusa will not off help on changing the ramming settings 🙁

Re: Still failing to print

I have only found physical reasons for stringing.

"Slow initial unload" I swear that is all I have messed with. I have not changed any settings. for ramming ect ect. printed nylon perfect, this weekend ill hit up petG and flex I hope. if time allows

Re: Still failing to print

What about ramming settings? Prusa will not off help on changing the ramming settings 🙁

Default Prusament PLA MMU2 settings are working best for me. The only thing I've changed (beside the obvious nozzle temp adjustment for each filament) is the "Loading speed at the start" set to 15mm/s to remove grinding during load.