PLA Breaking in Nextruder gears. Rare, but any Ideas.
 
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PLA Breaking in Nextruder gears. Rare, but any Ideas.  

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vhubbard
(@vhubbard)
Estimable Member
PLA Breaking in Nextruder gears. Rare, but any Ideas.

I have run my MK4 for months and built 2 others.  No filament feeding problems.   The nextruder can pull like an elephant.   Then I ran across Prusament PLA breaking in the nextruder gear.   When I checked the filament, it has about 2-300mm long brittle spot.  Any bending would cause it to break.    I finished out this spool and it had 3-4 of these spots.   When I gave the printer to my family, with a spool of PLA from a different batch,  they ran into it again.  I have not over-tightened the adjusters for the filament.   

Any ideas on preventing this?  Could a colder filament be part of the problem.  It is now winter here, rooms are colder and filament is outside of the enclosure.   

The problem is the sensor still thinks the filament is loaded, gears turn, but nothing comes out.   You have to pull the nozzle to remove the broken piece of filament.  I wonder if the MMU3 upgrade for the MK4 is addressing this.  There was mention of a change in the nextruder filament sensor for the MMU3.  

Posted : 09/12/2023 4:23 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: PLA Breaking in Nextruder gears. Rare, but any Ideas.

I had exactly the same problem, after a lot of time with support it was diagnosed as a damp reel of PLA, this despite it having been manufactured less than a month ago, having been open less than a week, and having been in a vacuum bag with silica gel when not actually printing. My conclusion was a dodgy reel of prusament.

I cooked the reel in a esun dry box for about 16 hours and it sorted it out.

Posted : 09/12/2023 4:37 pm
vhubbard
(@vhubbard)
Estimable Member
Topic starter answered:
RE: PLA Breaking in Nextruder gears. Rare, but any Ideas.

Time has provided some insight. 

Each break has been with multiple fine details on the same layer.  On small details the filament progresses little with a lot of reversing in the nextruder gears, The same spot runs through the gears many times. Wool on a small sheep,  A small dragon with lots of horns/spikes.    You can re-run the print and it breaks in the same general area.    A brittle spot in the filament may make it break easier.   Or was the spot embrittled by all the reversing?

When the filament breaks, the sensor shows it still loaded. The printer continues without any filament being put down. Print failure.   

Will back off the tension 1/2 a turn on the filament feed.  There wont be much tension left.  

With the MMU3, there appears to be a redesign of the filament sensor so that it will actually sense filament in the gears.  Hopping that when this is released it can sense a break and save a print.   It will require the nozzle removal to remove the broken filament. 

Summer vs. Winter room temperature may add to it.    I wonder if the dehumidifying process can make the filament a little more flexible.  Prusa now recommends it for even new filaments. 

What I have found is being submitted to Prusa. 

Posted : 27/12/2023 6:11 pm
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