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MMU2S Clicking - Extruder stuck  

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Kaeden B
(@kaeden-b)
New Member
MMU2S Clicking - Extruder stuck

I've been having issues with printing on my MY3S MMU2S. When printing, I hear a loud intermittent clicking sound and the filament doesn't flow consistently.

I've noticed that if I undo the two idler screws and open up the MMU the clicking stops, as the filament can move freely through the MMU. Therefore, I'm pretty confident that what's going on is that the MMU is blocking the printer from being able to pull filament, and the clicking noise occurs when the extruder motor builds up enough tension in the filament to force the MMU pulley motor to turn.

Any ideas? I made a brief video of the issue here:

This topic was modified 6 months ago 2 times by Kaeden B
Posted : 27/03/2022 12:43 am
BaconFase
(@baconfase)
Eminent Member
RE: MMU2S Clicking - Extruder stuck

You can still hear the extruder gears jump even when you have the MMU door open, so I don't think it's that.

Only time I've run into something like this was because of a bad spool of filament that just kept clogging the nozzle. Black PLA from the used-to-be-<$10 source. I junked the roll and got a new nozzle.

Posted : 28/03/2022 8:15 am
Kaeden B
(@kaeden-b)
New Member
Topic starter answered:
RE: MMU2S Clicking - Extruder stuck

Thanks so much for the reply!

The clicking you hear when the MMU is open is just the x-axis: the belt might be a little loose. When the MMU is open the print works flawlessly, just of course the MMU can't load or unload while it's open. But as soon as I close it I get the extruder clicking again and the filament flow becomes very inconsistent.

Do you know if the pulley motor (the one in the MMU with the long shaft and 5 filament gears on it) is supposed to turn with the extruder during the print? Or is the idler (the motor with all the little rollers on it) supposed to move out of the way so the extruder can pull freely?

Posted : 28/03/2022 2:27 pm
BaconFase
(@baconfase)
Eminent Member
RE: MMU2S Clicking - Extruder stuck

When the MMU is open the print works flawlessly, just of course the MMU can't load or unload while it's open.

Ah, I've run into this just once before as well. But it was with a roll of PETG filament that was strangely ribbed. Sounds strangely similar to your situation but I never figured out why it worked that way, so I only used it for single prints.

Do you know if the pulley motor (the one in the MMU with the long shaft and 5 filament gears on it) is supposed to turn with the extruder during the print? Or is the idler (the motor with all the little rollers on it) supposed to move out of the way so the extruder can pull freely?

Yes, once the extruder gears do their thing the MMU is supposed to release control: Idler barrel moves a little to release tension and the MMU gears shouldn't spin. So the last few seconds of your video looks normal.

 

Have you tried increasing the extruder idler door tension? Maybe it needs a bit more grip. Hard to tell where your setup is at since you have a modded extruder.

It doesn't look like you have a MMU rear passthrough mod installed. You could try loosening a screw or two by the filament 1 path; maybe your filament is getting pinched.

Posted : 28/03/2022 3:44 pm
Anachronist
(@anachronist)
Estimable Member
RE:
Posted by: @kaeden-b

I've noticed that if I undo the two idler screws and open up the MMU the clicking stops, as the filament can move freely through the MMU.

I had a similar problem and I solved it.

In your video, it appears that your MMU idler wheel is engaged when it shouldn't be. The idler drum should turn so that none of the wheels are engaged with the drive gear while a print is underway.

In my case, I realized that the shaft had slipped in the idler drum. The shaft is a tight fit, so it could still drive the drum, but the screw had come loose and the shaft had slipped, so the drum was out of alignment. This was also causing load failures.

If, while the unit is turned on, you can force the drum to turn until it stops (without forcing the stepper motor to turn), then your screw is loose. What I did was estimate where the center of movement was, tighten the screw gently, then turn it again to see if there was still any wiggle, and repeat. You don't want to tighten the set screw too much or  you can split the idler.

Once I fixed that, my load/unload failures stopped and the clicking due to the MMU stopped.

Now the position of the idler drum is something on my list of things to check periodically.

Posted : 28/03/2022 10:51 pm
Anachronist
(@anachronist)
Estimable Member
RE:
Posted by: @baconfase

It doesn't look like you have a MMU rear passthrough mod installed. You could try loosening a screw or two by the filament 1 path; maybe your filament is getting pinched.

I actually like this remix for M6 passthrough fittings by 8orge better (unfortunately not on Prusaprinters, 8orge has an account here, but he hasn't imported any of his designs): https://www.thingiverse.com/thing:3652406

That's what I ended up printing (before I even bought my MMU2S!). The reason is that all of the M10 fittings one can find are made in China and they use NPT threads (you can tell by the tapered diameter). It seems the manufacturers of these fittings don't know better. NPT thread's aren't metric, but the NPT threads at that diameter just happen to be close enough to 10mm metric threads that they fit for the distance you need to screw it in. However, because the diameter is tapered, all the threads aren't fully engaged, and I consider full thread engagement to be pretty important when screwing a metal fitting into a plastic part. So if you can find M6 passthrough fittings, use them. The thread diameter doesn't taper on those.

Posted : 28/03/2022 11:05 pm
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