Core One MMU3 Filament unloading getting stuck  

RE: Core One MMU3 Filament unloading getting stuck

Have you changed the festo fitting?
Prusa modifies the internal dimension to, I believe 2.6mm  for the MMU3, if you have n unmodified festo, that could be the reason for jamming!

regards Joan

RE:

Thanks for the quick response.  The festo is the one supplied by Prusa.  My MK4s was purchased late 2024 and the upgrade to core one was done in July 2025- The fitting is that which was shipped with one of those kits (can't remember)

RE: Core One MMU3 Filament unloading getting stuck

Has anyone else enountered this?

RE: Core One MMU3 Filament unloading getting stuck

I also have the same problem.

now the threading in the nextruder has worn out I end up having to put filament directly bypassing the festo.  The MMU unloads fine.  

I will try and print another top for the nextruder and replace with a wider hole festo.

Also the space above the nextruder is so little that the ptfe does bend too sharply.  I used the printables stiffner but this is a design flaw.

RE: Core One MMU3 Filament unloading getting stuck

Hello i have similar problem but i registered that filament is bendt, shifted as you can see. 

Its happening randomly same filament some time stuck some time is unloaded without problem. 

RE: Core One MMU3 Filament unloading getting stuck

I am having similar issues.  It appears the filament is not cooling sufficiently prior to unloading at the top of the Nextruder. 

I'm running a kit Core One with kit MMU3 and custom setup with custom feed tube length.  The MMU3 feeds and unloads thru the bowden tubes just fine and when I check tension by pushing or pulling at the disconnected Nextruder end, there is only light resistance.

During the unload sequence the Nextruder motor can be heard running backwards to unload and then the MMU3 takes over but because the filament has been squashed by the Nextruder drive gear and idlers into a flat strip, the MMU3 grinds away the filament at the idler.  It then tries 3 times to unload then gives a Finda error with no way to proceed except try again.  There needs to be a way to cancel without the MMU3 trying to re-home because at this point there is filament all the way from the buffer to the Nextruder.

As you can see this will never unload.  The only way I can see out of the situation is to pull the bowden tube from the INPUT of the MMU3, cut filament, pull the bowden tube from the Nextruder, cut filament and pull the filament out of the bowden tubes and MMU3.  Then I can hit the reset button to allow the Core One to cool down.  I have to hit reset because the UI is stuck at the Finda error screen with no option other than RETRY.  DON'T turn the power off  because you want the cooling fan on the heat break to run until cooled down!!!

Once cooled, I pull the Nextruder front cover, PG assembly and backing plate (don't lose the shim over the motor gear!) by removing the three front screws.  For reassembly you need to use the PG alignment tool and re-run the gear calibration as if you built the kit.

This is a total pain in the a$$ and it appears it must be related to the Tool change parameters in Slicer.  I'm using the stock Prusament PLA setting with Galaxy Black filament.  Is there a tutorial on adjusting these settings?

Any help would be appreciated!

RE: Core One MMU3 Filament unloading getting stuck

The first question that comes to my mind is, why does the filament get squashed flat.

- too much pressure (idler screw tension? Check build manual, screw tips should be level with the edge of the threaded part) 

- temperature: Does the interior get too hot? Temperature sensor, maybe? The material needs standard PLA temperature? Some of the Prusaments were somewhat different from generic plastics.

RE: Core One MMU3 Filament unloading getting stuck

Idlers are set properly.

Theory is that somehow filament is too hot when being unloaded.  Not sure how to check that.  Also this does not happen 100% of the time.

Chamber too hot?  Slicer settings for chamber do not seem to be getting to printer; exhaust fans seem to run no matter the slicer settings.

RE: Core One MMU3 Filament unloading getting stuck

Hello,  I am experiencing the same problem with the MMU. I have a core one kit delivered may 2025 so I guess my festo is the right one. 

I am using the MMU only for PLA though.  These are the following things I tried to solve it (but didn't lead to a consistent result were It didn't get stuck): 

Core one firmware version 6.3.4 and 6.4.0 alpha. 

Temperature: 190-220 

Cooling moves: 2-6 

Decreasing idler tension extruder 

Increasing idler tension MMU 

All this variable changes didn't result in a different tip forming. All of them  were almost identical like the picture of Vladimir D. 

My next step will be contacting support.

RE: Core One MMU3 Filament unloading getting stuck

Let me add my issue. CORE ONE upgrade kit from MK4 and MMU3. Lots of printing. So much I put in a new Nextruder PG Assembly and a new MMU3 plate set. O-ring is properly installed. Lately, after a long print with one colour, I have occasionally been finding squashed filament on my PG main ring. I take it all apart, clean, reinstall, calibrate, etc.

I’ve done this too many times. Any thoughts?

RE: Core One MMU3 Filament unloading getting stuck

Something similar happened few days ago. I fully cleaned the nextruder find out that metal wassher was missing and also i got in nextruder casing scratches/stamps. from the gear wheel. 
Still not sure how filamen can get there like tis but ...

The washer i that was missing:

PS: Used FW: 6.4.0-RC

RE:

So, just so you know i am not there yet.

But there is improvement. During my load filament test i heard clicking noise as if the gears were scratching against something before and after loading.

Turns out the noise of before loading was the sound of gears against my main plate (at first glance the plate seemed fine until i felt the edges where the gears make contact.

The rubber was in correct.

Anyways I had a spare main plate, took my time to double check if there was no contact with the main plate now. 

No noise when loading, but during unload there was still a noise, as if the unloading distance is too much.

This would be in line with my tip and with what carsonH is seeing (if you are printing on the hotter side)

Anybody knows where I can fiddle with the with the unload distance of the extruder? I want to see if this could be the solution.

I see different places of unloading so I'm uncertain which one is the correct one.

Ps. So far in getting best results from firmware version 6.3.4

RE: Core One MMU3 Filament unloading getting stuck

I've never managed to get the MMU working properly on the Core One, zero problems on the MK4S, but many cases similar to yours since I upgraded to the Core One: the filament tip isn't the same shape, it's too big and jams. I've used larger tubes and festos, but despite a slight improvement, it still jams. The cause: the filament tip is poorly managed. Thanks, Prusa.

Posted by: @kevin-maxey

Has anyone else enountered this?

RE: Core One MMU3 Filament unloading getting stuck

 

I am having similar issues.  It appears the filament is not cooling sufficiently prior to unloading at the top of the Nextruder. 

I'm running a kit Core One with kit MMU3 and custom setup with custom feed tube length.  The MMU3 feeds and unloads thru the bowden tubes just fine and when I check tension by pushing or pulling at the disconnected Nextruder end, there is only light resistance....

I have the same problem. I've tried everything, even switching back to a standard brass nozzle (non-HF), but still no clean results. I spend all my time manually removing jammed and broken filament. It's a real pain.

RE: Core One MMU3 Filament unloading getting stuck

Check out this thread for more help. https://forum.prusa3d.com/forum/original-prusa-i3-mmu3-assembly-and-first-prints-troubleshooting/core-one-mmu3-filament-blobs-around-gear/#post-765971

My setupworked fine for some time but this has started happening and you are right, very frustrating!!

RE: Core One MMU3 Filament unloading getting stuck

Looks like your are still running the original idler and filament sensor, these should be replaced with the replacement MMU versions

RE: Core One MMU3 Filament unloading getting stuck

I believe all reactions here switched their idler, main plate and sensor to the MMU version.

RE: Core One MMU3 Filament unloading getting stuck

I built the MK4s from Kit and swapped everything out when I added the MMU3. I then upgraded to Core One following the instructions. I never had any problems with this with the MK4s. It is problem with the Cor eOne

RE: Core One MMU3 Filament unloading getting stuck

Posted by: @blauwekat

Anybody knows where I can fiddle with the with the unload distance of the extruder? I want to see if this could be the solution.

There are "retract" parameters that probably fixed a stuck-filament issue for me yesterday.

The suspected root cause on my printer is too much heat getting past the "heat break" (which seems also consistent with soft filament wrapping around the nextruder gear in this thread - but I could be totally wrong).

What I did for my specific problem (clogged 0.25 mm nozzle with ASA - the setup worked perfectly fine with ABS but ASA is slightly hotter):

- Reduce retract distance.

- Reduce retract speed

- use thermal compound on the "cold" end of the nozzle for improved cooling.

There are also MMU settings in the print profile for the location and size of the "cold zone" relative to the nozzle. I will have a long, hard look at those if my printer keeps misbehaving (as in "soft filament getting stuck to the nozzle, requiring a drill to remove").