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[Solved] Extruder skipping and material buildup at filament tip  

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Bistromatic
(@bistromatic)
New Member
Extruder skipping and material buildup at filament tip

After years of outstanding reliability i've recently been running into some trouble with my MK3S:

I am attempting to print terrain tiles for wargaming and i've been getting some extruder skipping and underextrusion. Layer height is 0.1mm with otherwise standard settings, using PLA by Das Filament, freshly bought and unsealed. The problem mostly seems to occur near the end of printing the bumpy top surface of the tiles. It is not guaranteed to occur though, i have successfully printed a number of tiles already.


(aborted print with some underextruded layers)

My first suspicion was a clogged nozzle so i switched my old one out for a few E3D one, the problem persisted.

After some research i saw a few mentions that frequent retractions can cause skipping so i tried a print with retractions completely disabled, same problem at the same height.

I also tried both lowering and raising the extruder gear tension, again no difference. When i had a chance to observe the skipping directly, it was the extruder motor failing to turn the bondtech gears, not the filament skipping between the gears.

What i could determine so far is that there is a thickened section around the tip of the filament that seems to cause the trouble. This occurs regardless of disabled retractions.

I am currently running another attempt and there seems to be a slow build-up of this that can be cleared by unloading and re-loading the filament. The nozzle purge without any backpressure during the loading seems to do the trick. But obviously i'd like to avoid constantly babysitting running prints.

I'd be thankful for any advice or suggestions, as i have not found a solution for this specific problem despite attempts at research.

Best Answer by Neophyl:

That bulge on the filament does not look right. I’d check if the ptfe tube has shifted up away from the heat sink. Unfortunately to check that you need to at least partially disassemble the extruder. Prusa don’t fit the locking clip that is standard on e3d builds for some reason and over time the tube can work loose and it can then lead to problems with retractions and clogs. Print out some of the collet clips before you check and fit one anyway while you have it apart. 

Posted : 09/12/2021 2:50 pm
Lam
 Lam
(@lam-2)
New Member
RE: Extruder skipping and material buildup at filament tip

I have a very similar issue as you ancountered. When I am doing the first layer calibration or printing some small objects, there's absolute no problem. But when printing a large one (I mostly use 0.1mm layer height, prusament pla), there are always clicking sound and underextrusion in mid print

I have tried to increase the temperature and lower the rms but it did not solve the problem. When I pull the filament out, I got a "fuzzy" head as you do. 

Suprisingly, I increase the print speed for around 25% to 35%, clicking sound appear to be less happening and I am able to finish some larger print even the quality is not that good at all.

Posted : 09/12/2021 4:03 pm
Neophyl
(@neophyl)
Famed Member
RE: Extruder skipping and material buildup at filament tip

That bulge on the filament does not look right. I’d check if the ptfe tube has shifted up away from the heat sink. Unfortunately to check that you need to at least partially disassemble the extruder. Prusa don’t fit the locking clip that is standard on e3d builds for some reason and over time the tube can work loose and it can then lead to problems with retractions and clogs. Print out some of the collet clips before you check and fit one anyway while you have it apart. 

Posted : 09/12/2021 4:42 pm
Diem
 Diem
(@diem)
Noble Member

I agree with @neophyl, it looks like your PTFE tube needs replacing.  The locking clip is not necessary as long as you get the pressue on the tube high enough, it really is important to compress the tube properly...

In general, the smaller the layer height, the more important it is to have evrything else dialled in properly or the back-pressure causes problems.  I doubt you really need 0.1mm layers for terrain tiles especially if you are going to paint them. I would usually suggest 0.2mm which would ease the process and halve the print time as a side effect.

The fuzzy end suggests damp filament.

@lam-2 : check your belt tensions.

Cheerio,

Posted : 09/12/2021 5:23 pm
Neophyl
(@neophyl)
Famed Member
RE: Extruder skipping and material buildup at filament tip

For the sake of less than a gram of filament to print a clip out just to prevent any future issue I’d fit the clip. There is a reason that e3d include them when you buy a v6 hot end as fitted to the Prusa mk2/3 series. 

Im not familiar with das filament but I’ve noticed quite a few of the pla spools I’ve bought recently produce those fuzzy strings when unloaded, even when dry. Especially silks and some of the ones from 3dTomorrow that have a higher print temp range (up to 230 for pla).  

Posted : 09/12/2021 5:33 pm
Bistromatic
(@bistromatic)
New Member
Topic starter answered:
RE: Extruder skipping and material buildup at filament tip

Thanks for the quick replies y'all, i'll give the PTFE tube a look.

Posted : 09/12/2021 6:30 pm
Bistromatic
(@bistromatic)
New Member
Topic starter answered:
RE: Extruder skipping and material buildup at filament tip

Looks like it was indeed the PTFE tube, i changed it last night and so far i've completed one tile flawlessly and a second one is well past the critical height. Thanks again for the quick help.

Posted : 10/12/2021 3:33 pm
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