MMU2 repeated jamming mid-print  

Re: MMU2 repeated jamming mid-print

someone posted this.

" there's a hidden calibration you should probably plan on doing: calibrating the Bowden length. It's buried on this page: https://manual.prusa3d.com/Guide/Status ... 62?lang=en. I did this before trying to print on the advice of Prusa support, and my length was off by several millimeters. Going through this extra calibration step probably saved me an hour of troubleshooting."

hope it helps.

Re: MMU2 repeated jamming mid-print

I'd do the Bowden length calibration first. Mine was off by quite a bit (maybe 10mm) and it's plausible that could cause the problems you're seeing.

If that doesn't work...I haven't seen this myself, but others have posted here in the forum that it's possible to get strings in the Bowden tube which block the FINDA from registering the filament was fully retracted. I believe the solution is to print a few degrees cooler.

Re: MMU2 repeated jamming mid-print

Thanks for the quick suggestions. I'll do the bowden calibration and try some more tests. I'm already printing a bit cooler (195C) because I'm using Hatchbox PLA and I tend to get stringing if I go above that temp with it.

Re: MMU2 repeated jamming mid-print

Having some better luck now. Was able to complete the gecko in 3 colors and looks pretty good! (I hand-painted the black pupil in the eyeball.) I'll list what I did leading up to my success, in case it's helpful to anyone else who is just getting started with the MMU2...

1) I ran the bowden calibration as suggested above. Mine was only about 3mm off before calibration, but was off nonetheless. (If PRUSA is reading this, I would suggest making this a required step in the setup process. Although I read about it in the handbook initially, it is presented as an option that is only needed when you manually change the length of your bowden tube. I used the stock length, so I took that to mean this calibration was unnecessary.)

2) I had to adjust my extruder idler to make the bondtech gears line up properly. I noticed I was getting extruder clicking, and that the extruder was slipping occasionally. After tightening / loosening the tension screws in several different tests, it did not go away. I finally noticed that my idler gear was out of alignment. I had replaced the extruder body during the MMU2 installation process with the new B7/R3 extruder body that came with it. However there was no replacement idler part, so I reused my original R1 idler. Apparently there is a bit of a dimensional mismatch there, because it was impossible to get the idler gear to line up with the filament path given these two parts. I had to take the clear nylon washer from the left side of the idler part, and move it to the right side (so I have 2 washers on the right side and zero on the left) in oder to provide enough clearance to get the idler gear in direct alignment with the filament.

3) Without thinking about it, I had been using two different filament brands in the same print, Hatchbox and Paramount. In Slic3r I have defined these filaments as having different temperatures (195 vs 205), becasue Hatchbox tends to get stringy for me above 195C. While the printer was correctly adjusting the temp each time it switched between the two filaments, I suspect that this fluctuation may have caused some undue stress on the printing process, as Paramount filament doesn't print very well for me at 195C. Not totally sure about this one, but I changed over to using 100% Hatchbox for my test prints for now. Once I am printing more reliably I will start mixing filament brands again and see what happens.

After doing all this, I have observed no clicking or slipping in the extruder, and no jamming in the MMU! Definitely an improvement.

For now, back to testing.

Re: MMU2 repeated jamming mid-print

2) I had to adjust my extruder idler to make the bondtech gears line up properly. I noticed I was getting extruder clicking, and that the extruder was slipping occasionally. After tightening / loosening the tension screws in several different tests, it did not go away. I finally noticed that my idler gear was out of alignment. I had replaced the extruder body during the MMU2 installation process with the new B7/R3 extruder body that came with it. However there was no replacement idler part, so I reused my original R1 idler. Apparently there is a bit of a dimensional mismatch there, because it was impossible to get the idler gear to line up with the filament path given these two parts. I had to take one of the clear nylon washers from the left side of the idler part, and move it to the right side (so I have 2 washers on the right side and zero on the left) in oder to provide enough clearance to get the idler gear in direct alignment with the filament.
Good catch, this was certainly causing problems.

3) Without thinking about it, I had been using two different filament brands in the same print, Hatchbox and Paramount. In Slic3r I have defined these filaments as having different temperatures (195 vs 205), becasue Hatchbox tends to get stringy for me above 195C. While the printer was correctly adjusting the temp each time it switched between the two filaments, I suspect that this fluctuation may have caused some undue stress on the printing process, as Paramount filament doesn't print very well for me at 195C. Not totally sure about this one, but I changed over to using 100% Hatchbox for my test prints for now. Once I am printing more reliably I will start mixing filament brands again and see what happens.

I agree, I haven't tried to print with different brands of filament that print at different temperatures yet. It's hard to know if this is causing issues or not, so best to eliminate this variable until you're sure everything else is working.

Re: MMU2 repeated jamming mid-print

I hope I can get to where u are. The best result I can achieve is a mmu print with missing layers after multiple frustrating jams and alot of wasted filament.

Ive calibrated mmu to be spot on with Bowden length.
I've tried different tensions on mk3 idler door, Different tension, mmu idler body.
I've aligned the festo on top of mk3 extruder with small bowden leading to extruder while both had filament in place, then tighten screws.
I've tried using the supplied gcode sheep.
Tried my own ramming settings and different print temps with the sheep.stl
I've done cold pulls on mk3 extruder.
I triple checked the alignment of bondtech gears in mmu unit with filament in place during setting set screws.
Checked the alignment of bondtech gear and idler in mk3 extruder.

The problem is always constant jamming. It's stringing. The strings get caught and buildup over the life of a print. The strings will collect and cause a jam at mk3 extruder festo or bondtech gears or mmu festo or finda hole.

If not the stings its grinding at mmu bondtech gears which happens during retracts of filament for color changes. (Yes I tried tighter and looser tension on idler body)

1st layer, 1st color beautiful. Selftest during setup - congratulations you are perpendicular xyz....

It's the color changes over time.

Always after failure I remove all strings from festo, extruder mk3, mmu2, finda, start with new ungrinded filament.

Tonight I'll try expensive filament. After that idk...

Re: MMU2 repeated jamming mid-print

Since I’ve seen very little stringing on my MMU setup so far, I would suspect your filament and/or temperature is causing that. Try a different filament and maybe lower your temp?

Re: MMU2 repeated jamming mid-print

@josh.w3 You say you had 2 different pla filaments sat up to two different temperatures in slic3r for the Mmu 2.0 ,where in slic3r do you do this ?

Re: MMU2 repeated jamming mid-print

@josh.w3 You say you had 2 different pla filaments sat up to two different temperatures in slic3r for the Mmu 2.0 ,where in slic3r do you do this ?

On the filament tab, you can change the print temps and save as a user-defined custom filament config. Then on the main screen in MMU-mode, you can choose a different filament definition per extruder.

Re: MMU2 repeated jamming mid-print

Tonight I'll try expensive filament. After that idk...

The cost of the filament has no relationship to the quality or whether or not it will string.

But it sounds to me like you're on the right track, since the filament is the next obvious variable to eliminate.

I have a crazy experiment to suggest: Do you still have any of that Prusa silver left over from when your MK3 was new? If you do, try using that for both inputs for printing the sheep. It seems dumb to do a multimaterial print by switching between the same two filaments, but my theory is that Prusa should have tested the MMU with its own filament. So the odds of success are higher if you use that stuff.

Re: MMU2 repeated jamming mid-print

@josh.w3 You say you had 2 different pla filaments sat up to two different temperatures in slic3r for the Mmu 2.0 ,where in slic3r do you do this ?

On the filament tab, you can change the print temps and save as a user-defined custom filament config. Then on the main screen in MMU-mode, you can choose a different filament definition per extruder.

Thank you very much for the answer ,but i can't get it to work .When i save the custom filament config ,i can only load one setting for filament ,and i can't choose or see the "saved" filament in the selection folder to the 5 filament / extruder on the main page , i must be doing something wrong .
I will keep on trying 🙂

Re: MMU2 repeated jamming mid-print

@josh.w3 You say you had 2 different pla filaments sat up to two different temperatures in slic3r for the Mmu 2.0 ,where in slic3r do you do this ?

On the filament tab, you can change the print temps and save as a user-defined custom filament config. Then on the main screen in MMU-mode, you can choose a different filament definition per extruder.

Thank you very much for the answer ,but i can't get it to work .When i save the custom filament config ,i can only load one setting for filament ,and i can't choose or see the "saved" filament in the selection folder to the 5 filament / extruder on the main page , i must be doing something wrong .
I will keep on trying 🙂

Solved it 🙂 . The saved filament files did not get saved in the correct folder ,for what ever reason ? ,now i can see and choose for each extruder 😀 ,again ,thank you very much for helping me 🙂

Re: MMU2 repeated jamming mid-print

Tonight I'll try expensive filament. After that idk...

The cost of the filament has no relationship to the quality or whether or not it will string.

But it sounds to me like you're on the right track, since the filament is the next obvious variable to eliminate.

I have a crazy experiment to suggest: Do you still have any of that Prusa silver left over from when your MK3 was new? If you do, try susing that for both inputs for printing the sheep. It seems dumb to do a multimaterial print by switching between the same two filaments, but my theory is that Prusa should have tested the MMU with its own filament. So the odds of success are higher if you use that stuff.

I'm at work now. I'm almost certain I have some prusa silver pla leftover. I probably have some other color prusa branded pla as well. Have some hatchbox, as well as some more premium filaments. I just never want to use those up. Only for showing off, gifts, models for customers etc.
Ive been printing with inland for nonsense prints because it's cheap and prints very well. (I'll have to find the proper settings that make inland work well with mmu2)
Although I tried printing inland with a higher temp, I don't remember if I tried printing inland at a lower temp. I was trying to use the supplied gcode sheep to eliminate my novice understanding of mmu slice settings as the issue. Inland clearly needs different settings.

I bet prusa filament, prusa sliced gcode I'm good to go. It's certainly something to try next anyway.

Thanks for all your help, thus far.

Re: MMU2 repeated jamming mid-print

Significantly better with prusa filament silver and black hatchbox. Only one jam at end.

Thank you PJR