MMU2 Troubleshooting  

Re: MMU2 Troubleshooting

Hey everyone,

I've assembled the MMU2 for my MK2.5 printer. Assembly went really well and everything appeared to be working as expected. When I attempted to print a 2 color Benchy, I began to have issues with the mechanics of the MMU2 system, specifically the filament loading pulley. In short, the MMU2 pulley is pushing too much of the filament into the extruder which forces the filament to jam against the bondtech gears causing the MMU2 pulley gears to take a bite out of the jammed filament. The result of this missing bite in the filament causes load/unload failures at random intervals during prints. Basically, the MMU2 pulley is pushing too much filament into the extruder and eating up the filament.

I've followed the individual filament calibration manual here: https://manual.prusa3d.com/Guide/Service+menu+-+Individual+Filament+Calibration/842
and also read on this thread to go through the process 3 times, so I've done that too. I continue to face the same exact issue and get failed prints.

I decided to try something different and calibrate the individual filament lengths about 5mm shorter than the manual suggested. This appeared to help, but the issue still persists albeit significantly reduced. 🙁

I'm a bit confused as to what is happening here, because I think I'm doing the calibration correctly, and don't think I should have to deviate from the manual at all really, never mind the 5+ mm I'm doing to get my prints to succeed.

Does anyone have any ideas as to what I could look at to help explain why I'm getting the behavior I am?

Re: MMU2 Troubleshooting

do you have some filament paths that work good?

Re: MMU2 Troubleshooting

Hi there, please excuse the ignorance, but I'm not sure I understand what you are asking.

I know that the spools are setup using the Prusa filament holders, which work well enough, the filament moves smooth through the PTFE tubes and when there aren't chunks taken out of the filament from the MMU2 filament pulley, the filament works well through the rest of the printer into the extruder. Is that what you were asking?

Re: MMU2 Troubleshooting

have you noticed it doing that on EVERY filament channel? I had my fights with filament path 1 3 and 4 but the other 2 have been fine almost the whole time. if you get what I mean.

Re: MMU2 Troubleshooting

I understand now. I've only tried with path 1 & 2 for this Benchy print.

I'm not sure it's a physical path issue, because I can easily push non-mangled filament from the spool holder all the way to the extruder, by hand, from either path 1 through 5.

When the printer attempts to switch colors, I can see the filament come into the extruder (being driven from the MMU2 pulley) and slam into the extruders bondtech gears, which then results in the filament stopping and the MMU2 pulley grinding up the filament.

Re: MMU2 Troubleshooting

are you filaments calibrated to the top (ish) of the extruder gear?

Re: MMU2 Troubleshooting

I've followed the individual filament calibration manual here: https://manual.prusa3d.com/Guide/Service+menu+-+Individual+Filament+Calibration/842
and also read on this thread to go through the process 3 times, so I've done that too. I continue to face the same exact issue and get failed prints.

I decided to try something different and calibrate the individual filament lengths about 5mm shorter than the manual suggested. This appeared to help, but the issue still persists albeit significantly reduced. 🙁

I've tried what the manual says and my own attempt at compensating for whatever is wrong.

Re: MMU2 Troubleshooting

and they stay consistent when calibrating? hmm im thinking...

Re: MMU2 Troubleshooting

Yes, they remain consistent. I kind of wish they didn't, because it would be easier to point at the problem.

Re: MMU2 Troubleshooting

I do know some people loosen up the 2 screws on the "extruder cap". that might give you more play to be able to print while figuring out the bigger issue. I think some people add springs to the cap screws.

im still trying to think of something besides the firmware acting up.

Re: MMU2 Troubleshooting

I do know some people loosen up the 2 screws on the "extruder cap".

The cap that sits on the extruder right above the laser based filament sensor, with the tiny PTFE tube in it? It appears as if the filament sensor isn't being used (at all) with the MMU 2 system, so that could probably work... I'll try it on the print right now.

Re: MMU2 Troubleshooting

ya, the cap moves abit instead of the filament grind. I did it for awhile. its almost like it's tipping its hat to you when it loads. semi comical. maybe ill go back to doing it but make a little guy with a hat on the top cap 😀

Re: MMU2 Troubleshooting

I just tried that and had no luck. It appears as if the MMU2 pulley is forcing too much filament out for that trick to work in my situation...

I just canceled the print... Way too aggravating 😡 😥 👿

Enjoy the failure so far!

https://lh3.googleusercontent.com/HVMQAnS04UnLR66wxGEASVLJ4HW9lsw5xgIT4Ji7SmTpEb8D4WODA2HKRV9RNNJQL1cftBBnwNiyKINdVX2f-uPmzavBsBTUo2wPBxQzh64t8le3oVkSawex8xxerIqAtcVzb9g_r4o=w300

I also just realized something. The selector device is NOT aligning with the filaments correctly... Look at the alignment after rebooting the printer and then when I manually aligned it...

Prusa alignment after self calibration:

My manual alignment (which is better but still off in the other direction):

Re: MMU2 Troubleshooting

I was able to "fix" the misalignment by printing up some shims and taping them into place. Now that I know the thickness I need, I'll print a final version that snaps into the hexagon in the frame of the MMU2 instead of just being taped to it. The thickness I needed was .9 mm + .2 mm.

The original problem I posted about still stands though... If anyone else has ideas, I'd be more than happy to entertain them!

Re: MMU2 Troubleshooting

nice find, maybe recalibrate it again now that that hole is running clean.

Re: MMU2 Troubleshooting

nice find, maybe recalibrate it again now that that hole is running clean.

That would be nice if it worked! I'll try that and report back.

Re: MMU2 Troubleshooting

If you are getting misalignment of the selector, "fixing" it by "padding" the left side (from the front) is not the right thing to do.

There could be a couple of solutions:

A drop of oil on both rods
Something on the right side is assembled incorrectly or preventing the selector from homing to the right.

Peter

Re: MMU2 Troubleshooting

but at least that solves the issue I bet. if he is like me. he is printing and we wont know until its done 😀

Re: MMU2 Troubleshooting

If you are getting misalignment of the selector, "fixing" it by "padding" the left side (from the front) is not the right thing to do.

There could be a couple of solutions:

A drop of oil on both rods
Something on the right side is assembled incorrectly or preventing the selector from homing to the right.

Peter

The rods are already oiled; I did that during assembly. If I remove the motor, I can easily move the selector from left to right, across the entire length of the rods - there is nothing that appears to be assembled incorrectly and nothing binds. I can do the very same w/ the motor installed (rotating the motor by hand). Also, the MMU2 doesn't home on the right (past filament 5), it homes the selector by moving it all the way to the left (filament 1 position) and forces it to skip steps (exactly like the Z-axis alignment does). The shim is totally goofy, but what other options can you provide to force the system to align correctly?

but at least that solves the issue I bet. if he is like me. he is printing and we wont know until its done 😀

So far the shim has been working very well. Filament moves even better through the while system. I've made some other changes recently and will be testing it out to see if it's working better and will report back.

Re: MMU2 Troubleshooting

its nice you figured out whats going on with your mmu. I still haven't looked at my holes, but I did enlarge them long ago.