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Chewing through filament - help!

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I'm at my wit's end with this.

I'm using an Ultimaker 2-Extended that I've had for about 2 months. Current stats are 347 hours on, 318 hours printing, 246 meters of material. In the past week or so, I've started to run into big problems with extrusion, where it will just start to spit out thin blobby strings and then stop extruding altogether. The culprit seems to be the feeder motor chewing through the filament and not being able to feed.

I did several "atomic" pulls, and everything looks good there. I'm certain my teflon isolator is not at issue here, as I can easily hand-push the filament through when the nozzle is hot. It extrudes nicely and I cannot detect any reason that the hot end would be to blame here.

I ran a lightly oiled swab through my Bowden tube, and even greased the spool holder to make sure there was minimal friction for the feeder to fight. Everything moves like butter.

Then I adjusted the knurled feeder wheel tension a little tighter to give it more grip on the filament - about a third of the way to maximum. That seemed to help a little bit, but I'm running into the same issue again. This is happening on prints that I've done many times without any problems, and using the same brand filament (Ultimaker silver PLA). It always seems to come down to the point in a print (usually about 1 to 2 hours in) where it's doing a lot of retractions - it just gets to the point where it chews right through the filament.

I'm getting sick of throwing filament in the trash every time this happens, and wasting time printing partial prints that go in the trash too. I've tried modeling these parts differently to minimize retractions, but there's only so much I can do with it; they're complex parts. I've tried turning retraction off, which makes a huge mess on the print and gives me poor quality results.

I'm hesitant to start monkeying around with temperature or print speed, because I've printed these items before at the same settings with no issues. What else should I be trying to fix this problem? Is there a maintenance issue I haven't checked? Should I continue to tighten the feeder wheel tension even further, or will this just make it worse?



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There are a few things you can do. One simple solution is to reduce the amount of retractions. I was printing "big ben" and it kept doing what you describe on a particular section. I found that slice and there were 40 retractions. It was one retraction every .159mm or 24 retractions for every spot of filament on that layer. So I set the minimal extrusion parameter to 0.32mm. I had 19995 retractions in the resulting gcode instead of 34300 retractions. That was enough that I was able to print big ben and the stringing appeared to be no worse visually.

A second solution is to adjust the tension. Looking at the "clean" part of your filament (bottom part of picture) I would guess your tension is too light. Try tightening it a bit - try to get the diamond pattern in the filament a little more severe.

I have a different UM2 that is older and has a different spring. That one seems to have less tension on the spring yet it has deeper cuts into the filament. I'm not sure what the tension is. That older UM2 once did the eiffel tower which had 42000 retractions on just the bottom section which is 231 meters of retraction (I had retraction distance on 5.5mm at the time - have since gone back to 4.5mm) or each piece of filament going through the feeder 9 times. Less than that difficult layer on big ben but still that's just the average. Some layers probably had much more.

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OK, I tried tightening the feeder tension a bit more, and all was going well until about an hour into the print, where I ran into extrusion problems again. This time it didn't chew through the filament (though I did see where the teeth marks had gone back and forth over the same piece several times).

I had noticed low extrusion early on in the print, so I tuned it to 105% material flow. That didn't do much, so I upped the temperature from 210 to 220 and backed the material flow back to 100%. The higher temperature worked for a while, but then for no explainable reason, it just started thinning out and stopped extruding altogether.

So now I'm really confused as to where the problem lies. Since it didn't chew through the filament this time, it appears to still be feeding. But not extruding.

My UM2-E came with a spare nozzle, spring, isolator, and other hot-end parts. Is it worth just swapping those out and seeing if it fixes the problem? If so, where would I find instructions on how to do this?

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These 2 videos at this site would be helpful:


It's not chewing through filament? Then you probably have a totally different, unrelated problem.

Maybe printing too much volume too fast?

Here are my recommended top speeds for .2mm layers (twice as fast for .1mm layers):

20mm/sec at 200C

30mm/sec at 210C

40mm/sec at 225C

50mm/sec at 240C

The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion. Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp. But don't go over 240C with PLA.

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Did you ever find a proper solution to your problem Tobus?  I am having this exact issue with Wood filament only.


I figured I'd just pull a big load of filament off of the spool to try and get past the 'bad' area, it was a theory... Turned out to be spot on I suppose, working handy dandy now :]

*Update again*

Looks like the issue is not resolved. I am going to wait until it is not raining to see if it is the filament absorbing moisture. I can load it just fine, it comes out of the head and everything, then mid print just stops extruding. If I catch it I can jack the temp up and keep it going, but I am printing with material that prints best at 190°c at 230°c already so it bubbles a bit coming out as is, I don't want to turn it up any more than that, so I am sort of stuck here.

Edited by Guest

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Woodfill is best printed with 0.6mm nozzles or larger. If printed with 0.4 nozzle then I recommend layer heights of 0.2 and fastish speed to keep it consistently flowing.

If you have more issues then maybe best to start a new topic for tips on printing with woodfill

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