MMU2 Loading/Unloading and Extruter Problems  

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andrew.reagan
(@andrew-reagan)
New Member

I installed the MMU2 to a Original Prusa MK3. I got about half way through the first print and then the loading and unloading started to not work. The filament would only make it halfway up to the extruder. On some occasions, filament would fail to unload from the extruder. Now filament will not eject from the extruder at all, even after the rare successful loads.

I am considering removing the MMU2 upgrade. Would I just do the installation steps in reverse or is there an actual procedure to do this?

 

Thanks,

Andy

Posted : 18/11/2019 6:49 pm
erick.k liked
Paul Mullen
(@paul-mullen)
Active Member

I haven't seen any un-installation instructions, but you can probably just do it in reverse.  

But if I'd love to encourage you to give it another try.   There are a lot of potential sources of help here in the forums, including some mods that others have found helpful.  Two observations from my experience:

1) The MMU and associated changes to the extruder assembly are not as tolerant to "just put it together" as the printer itself is.  There's a lot more care required to align things well.  In my case, it was largely getting the IR sensor right, but others have had other problems.

2) Unlike the printer alone, the MMU requires more "preventative maintenance."  The MMU gets a lot of filament scraps and other crud in it as a natural reflection of how it works.  You'll have to clean it out occasionally.

3) Filament quality matters.  I don't know how to provide guidance here, but I know that especially some filaments that get moist from being out of their packages are troublesome.  They're easy enough to dry out again, by putting them in a 170-degree F oven for a couple of hours.

We're all here to help.

Posted : 28/11/2019 2:11 pm
PPRRUUSSAA
(@pprruussaa)
Trusted Member

I think, you have a flickering filament sensor, because it is not correctly aligned. Please check the sensor readings with SupportMenue and adjust the sensor. I had the same problem. Some debris of filament at the extruder gear, often is the problem. The sensor is tetecting false, that the filament ist already in the the extruder. The it can not feed it into. Again false/right detecting the filament, an then unloading.

I have made this modification to detect the sensor problem. And it worked for me very well. Detecting debris and adjusting the sensor.

This post was modified 1 year ago by PPRRUUSSAA
Posted : 28/11/2019 2:20 pm
erick.k
(@erick-k)
New Member
Posted by: @andrew-reagan

I installed the MMU2 to a Original Prusa MK3. I got about half way through the first print and then the loading and unloading started to not work. The filament would only make it halfway up to the extruder. On some occasions, filament would fail to unload from the extruder. Now filament will not eject from the extruder at all, even after the rare successful loads.

I am considering removing the MMU2 upgrade. Would I just do the installation steps in reverse or is there an actual procedure to do this?

 

Thanks,

Andy

Did you ever find a resolution? I'm having exactly the same problem. It's like the PTFE from the MMU2S to the extruder needs to be slightly wider to accommodate a slightly bulbous tip on the retraction. In my case the bondtech will never fail to feed it if I give it some help to get the filament there - but it's too large for the long PTFE and the weaker pulleys in the MMU. I read on Reddit where someone upgraded to a wider 2.5mm PTFE and drilled the connector at both ends to accommodate the thicker PTFE. He claims this solved this issue permanently. I can overcome the log strings with temperature tuning, but the shape of the tip after the retraction is always larger than 1.75mm - I've never seen an unload look any different - so it seems off this tight tolerance would be there when arguably it's not even necessary - just a hinderance.

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Posted : 29/11/2019 8:10 pm
huskyte
(@huskyte)
Trusted Member

Please read the following post by me: https://forum.prusaprinters.org/forum/original-prusa-i3-mmu2s-mmu2-hardware-firmware-and-software-help/mmu-experience-from-no-chance-at-all-to-an-all-week-running-machine/

There was, at least for me, no reason for a wider PTFE tube. All issues could be related to 2-3 root causes that are easily fixed. Tips are overrated as I recently stated. Mine can't even be pulled backwards through the MMU. It is all about heat creep and proper sensor adjustment plus as umaker declared a cleaning routine. I usually get an issue roughly every 7000-12000 filament changes... and I have two printers running nonstop.

Posted : 03/12/2019 9:33 pm
erick.k
(@erick-k)
New Member

Thanks. Turns out the problem was my heat break. I had an original MK2S hot end because I had never installed the MMU kit - which came with a whole new hot end. I dug the new one out of my spare parts and installed it. No further issues so far!

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Posted : 03/12/2019 9:36 pm
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