Extruder is clogged after an hour of printing on MMU2S with MK 2.5S
 
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Extruder is clogged after an hour of printing on MMU2S with MK 2.5S  

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konstantin.d2
(@konstantin-d2)
New Member
Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

I have completed MMU2S Upgrade. Have installed the latest versions of firmware and software. I am having currently a number of issues while printing with Innofil PLA, the worst is - after an hour or so of printing the extruder starts making a clicking sound, the extruder gears are trying to spin, visibly trying to push the filament further into the extruder. After a few moments the filament either gets unloaded with an error 'filament load failed' or the extruder continue moving is if during printing but no filament is coming out of the extruder with extruder gears clicking and not moving.

This was an upgrade from MK2.5. While MK2.5 with a single filament it was printing  flawlessly, I never have any issues with it.

After doing some research, it seems the most possible cause of this - is the filament gets built up inside the heat break and clogs it because there is not enough thermal conductivity between the heatbreak and the heatsink, thermal paste must be applied. 

Does it sound right, or could there something else to it?

If my assumption is correct, why it never happened before, when I was printing with a single filament?

I am now required to unscrew the heat block, the heatbreak and apply thermo-paste on the heatbreak longer threads? Will I be able to do it without taking apart all the extruder assembly?

Thank you in advance for any comments/suggestions!

This topic was modified 2 years ago 2 times by konstantin.d2
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Posted : 03/06/2019 6:07 pm
konstantin.d2
(@konstantin-d2)
New Member
Topic starter answered:
RE: Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

No ideas? I did a cold pull as some advise, looked clean. took the heat block out with the heatbreak, applied thermopaste, screwed back on tightly. Now the printer can't do Z calibration. Extruder goes all the way up, then down, as soon as it reaches the print bed, calibration stops with an error 'Calibration failed. Check axes and try again'

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Posted : 05/06/2019 2:04 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

Regarding the jams themselves. Are there a lot of retractions in the print (hopping from one place to another) with little printing in between the retractions? The Prusa heat break is stepped inside (reportedly for the MMU) and that has been attributed to causing jams on prints with lots of retractions (it hit me with the last print I was working on before I added the MMU, I never got the print to work without a jam). Also remember that the default profile in multi-tool mode prints colder than the Single profile (or without the MMU at all). It could be that your filament does not like that colder temp and you need to adjust it in the print settings.

As far as the Z calibration issue, I'm not familiar with the 2.5. The last time I rebuilt my extruder (due to a jam that left about 2" of filament in the heat break and 2cm jammed in the top of the PTFE) I had similar issues with being unable to calibrate (though for me it would not find home). Manually using the "Move Axis" functions showed that everything appeared to work as expected. After lots of futzing around I finally ran Selftest rather than the XYZ calibration. I forget what it complained about, but it led me to looking at the extruder assembly and it turned out that I tightened the extruder onto the X carriage too much and was causing just enough compression on the bearings that it was causing problems. Once I loosened that a bit it calibrated and has been happy since.

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Posted : 05/06/2019 2:57 pm
konstantin.d2
(@konstantin-d2)
New Member
Topic starter answered:
RE: Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

Thank you for your reply. There are not many retractions and I have set the retraction to less than 1mm. I have also tried printing with different temperatures from 200C to 220C which seems to have little effect on jams. I have confirmed the jam happens somewhere inside the heatbreak. After the extruder is clogged and cleaned, I am able to print consistently a number of layers before it starts clogging up again and the filament is unable to load.

I have taken apart the extruder and applied a thermopaste on the threads of the heatbreak which go into the heatsink. I have made sure I tighten the heatblock while it is hot at 280C, as well as tightened the nozzle.

The first time I have tried to print , it allowed me to print for more than 1 hour before the jam occurred. Now it consistently jams after 15-20 min in the print.

The Z calibration issue is fixed. Apparently there was a bad connection somewhere inside the Rambo enclosure. 

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Posted : 06/06/2019 6:03 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

Have you tried a different filament to see if it has the same issue? In the case I mentioned I was trying to use the Prusa Silver that came with the printer which had always been my go to filament for great prints (and had gone through about 100 hours of similar printing with no issues). Using the same gcode I was able to complete the print with both Amazon and Superfila filaments (just the wrong color so useless other than leading me to doubt the filament).

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 06/06/2019 6:11 pm
konstantin.d2
(@konstantin-d2)
New Member
Topic starter answered:
RE: Extruder is clogged after an hour of printing on MMU2S with MK 2.5S

Finally, success!! I have ordered a different filament to try, but while waiting for it, I stumbled on a thread which didn't see before: https://forum.prusaprinters.org/forum/original-prusa-i3-mmu2s-mmu2-hardware-firmware-and-software-help/success-how-i-resolved-my-mmu2-issues-mk2s-mk2.5-mmu2-upgrade-path/#p124846

I went the same route and now the printer is printing for more than 24 hours straight without a single jam either in extruder or mmu2s! Unbelievable! 

The cause: It appears that the internal diameter of the mk3 heatbreak is smaller than the one of MK2/MK2.5, and this is the cause of jams for a lot of people with older upgraded Prusa printers.

What helped me: I have replaced the heatbreak with mk3 version and did some settings adjustments as described here: https://www.thingiverse.com/thing:3217915

I have also changed the number of cooling moves to 2.

I have to note that I measured the inner diameter of the mk3 heatbreak as 1.8mm and the older one I have 2.2mm.

 

 

 

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Posted : 20/06/2019 5:53 pm
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