Under Extrusion problems

[DPL 0]

Hi All,

I have used my Ultimaker2 reliably for about a year, but now have underextrusion problems, and the symptoms have been getting worse. The feed used to occasionally skip back (make that thunk sound) and under-extrude the first layer. Now, extrusion will fail completely, with the feed gear chewing into the filament. So far, I have:

- re-levelled the base plate

- Cleaned out the hot end many times using the Atomic method. Plugs come out clean.

- Disassembled the bowden tube and blown it out with compressed air

- Checked the set-screw tightness on the advance drive gear and blown out any debris

- disassembled the hot end and removed a slight lip from the teflon coupler

What's frustrating is that there does not seem to be any friction at any of the individual assemblies:

- When inserting a length of filament by hand into the hot end for the Atomic cleaning method, the plastic extrudes nicely from the nozzle, with minimal pressure.

- There are no whispy traces of filament or debris in the Bowden tube, and with it off the machine, a length of filament slides easily through it.

- When loading filament, using the advance-material function moves the material reliably, so it seems like the advance mechanism is fine.

However, when all reassembled, even the load-new-filament process ends up with the drive gear chewing into the filament.

The filament is Ultimaker PLA, and that's the only plastic the machine has ever seen. I've ordered a new hot end, but was wondering if there is something I haven't thought of.

Thanks!

[gr5 2,173]

However, when all reassembled, even the load-new-filament process ends up with the drive gear chewing into the filament.

That's strange. That sounds like there is a huge friction in the tube itself. Is it possible you bought some 3mm filament by accident (instead of 2.9mm or 2.85mm)?

when you had the bowden disassembled did you try pushing some filament through it?

Does it grind even before the filament reaches the head? while it's still part way through the bowden tube?

[DPL 0]

 

However, when all reassembled, even the load-new-filament process ends up with the drive gear chewing into the filament.

That's strange.  That sounds like there is a huge friction in the tube itself.  Is it possible you bought some 3mm filament by accident (instead of 2.9mm or 2.85mm)?

when you had the bowden disassembled did you try pushing some filament through it?  

Does it grind even before the filament reaches the head?  while it's still part way through the bowden tube?

 

gr5, thanks for your reply. The filament is marked 2.85 mm, and measures 2.8 with my calipers. With the Bowden disassembled, filament did slide easily through it's whole length, and it only grinds once the filament get to the head. so I guess that implies there is a high resistance at the head that is somehow not evident when the pushing filament into the hot end by hand (without the Bowden tube).

[yellowshark 153]

Strange indeed. A pure guess; have you got a wrong setting in Cura somewhere that is causing the drive mechanism to push through more filament than the hot end can extrude - you know like print speed set to 400 instead of 40?

[gr5 2,173]

Is the feeder stepper really hot? Sometimes it is hot enough to soften the PLA right at the feeder knobbed sleeve.

Maybe you need to explain better about the "change filament" grinding. Is it happening only when the material gets into the head? Or when it is part way through the tube.

You might want to remove the bowden at the feeder and inspect it for over-crimp there which can cause problems.

[DPL 0]

Is the feeder stepper really hot?  Sometimes it is hot enough to soften the PLA right at the feeder knobbed sleeve.

Maybe you need to explain better about the "change filament" grinding.  Is it happening only when the material gets into the head?  Or when it is part way through the tube.

You might want to remove the bowden at the feeder and inspect it for over-crimp there which can cause problems.

 

Thanks for the replies. To explain better, the filament moves through the Bowden tube OK until it gets to the hot end. Then the feeder starts skipping. The feeder does not seem to be getting hot. Last night I thought it was because the Bowden tube wasn't fully seated into the Teflon adapter at the hot end, but this morning the problem is still there. Using manual control to advance the material (nozzle at 210C), the feeder skips back. The hot end is actually hot, since a piece of filament melts if touched to the nozzle. At this point my next move is to replace the hot end, since all evidence points to a high resistance there.

I don't think the Cura settings are off as I always use the "quickprint" (High Quality) default settings.

Thanks again for the help.

[gr5 2,173]

Then the feeder starts skipping.

Oh! That's normal. If nothing is coming out then it may be getting hung up on an internal ridge. Try cutting the tip of the filament to a point and reinserting it. Or go to move material and move it up and down a few times watching the filament and grabbing the bowden and pushing it a few different angles so the filament approaches slightly different each time. Usually what I notice is suddenly the filament starts moving again another 10mm before finally coming out of the nozzle.

Alternatively you could have a plug. A small piece of sand or dust can get carried up through the bowden and into the head and cause a plug. Best remove with cold pulls or you can remove the whole nozzle assembly and burn it out clean.

I guess reading all your posts I'm just completely confused. Are you saying you get nothing out of the nozzle during filament load? if you do get filament but it's skipping - that's completely normal. Or are you saying move-material works fine but when you print the print doesn't look so good? I think you should start over and explain what the problem is because I'm getting conflicting information.

[gr5 2,173]

Maybe the problem is we disagree what "grinding" means. To me grinding is when the filament is ground down and you get a bite mark out of the filament. Or alternatively the filament is ground flat on one side so instead of a cylinder coming out of the feeder you get a half cylinder.

I think maybe you just mean the "skipping" sound is grinding? If so that means everything you said is now taken in a new light and maybe you just have normal underextrusion which is a whole different topic than grinding or plugs.

[gr5 2,173]

I have to say words are not the best way to communicate sometimes. A video or photos is usually better. That way the term "grinding" is clear to everyone.