Nozzle clogs and there is a bulge on the filament end

[Elaup 2]

Hi there, community!

I repost this message as it was in the wrong category.

I'm requesting feedback on an under-extrusion issue I need to solve. After a few successful prints on my UMO+, the extrusion stops generally at the second layer, especially for large parts. I've checked the feeder and I did a few trials after Atomic methods that seemed to work well.

When I pull out the filament after the failed print, it has a "collar" shape, like ten milimeters above the cone.

I'm wondering if this may have a link with my under-extrusion problem or if it is normal to have such a shape on the filament end?

Thanks in advance for helping a noob!

[SandervG 1,221]

Hi @Elaup,

Thank you for your message. Most likely there is a problem with your bowden tube.

Either the bottom tip is not 100% flat / aligned with the surface it should connect with (the ptfe coupler), or the bowden tube can move up and down. This can be because the horse shoe and coupler have lost grip, or perhaps it is just not fully inserted.

If there is a gap between the bowden tube and the part underneath, and the heat has a change to crawl up in the filament, it can expand the filament in this area and once it became fatter it will cool and can not move up or down.

You may also want to look at your printing temperatures, if they are perhaps not too high, however, if the problem indeed lies with your bowden tube you need to address this no matter what. Good luck!

[Elaup 2]

Hi @SandervG and thank you for your answer!

You was right, I checked the bowden tube end and I noticed it was not cut perfectly straight. So I cut it again with a sharp ceramic knife. I inserted it while paying attention that it did not move up when I locked it with the blue clip, and now it seems to be much better now.

I'll try to print a larger part to see if the problem happens again!

Thanks again for your advices!

[Elaup 2]

Hi @SandervG and thank you for your answer!

You was right, I checked the bowden tube end and I noticed it was not cut perfectly straight. So I cut it again with a sharp ceramic knife. I inserted it while paying attention that it did not move up when I locked it with the blue clip, and now it seems to be much better now.

I'll try to print a larger part to see if the problem happens again!

Thanks again for your advices!

[Elaup 2]

Under-extrusion came back when I tried to print a larger part. The nozzle completely clogged at the second layer. I checked the filament and the bulge is much smaller but still here.

Should I try to cut the bowden end again? I'm not sure I could be more accurate...

Thanks again for your help.

[SandervG 1,221]

How often have you cut it? If you have cut it too much or too often, there is a chance it is too short. When your print head moves to the front of the machine this can create pressure on the filament, create a hard angle where it enters the head but also pull it out of its socket and creating an opening again at the bottom.

By heart it should be 68cm long. Can you measure how long your bowden tube is?

[Elaup 2]

Thank you for your answer @SandervG.

It was the first time I did it and I just removed a few milimeters, maybe three. Do you think it is ok and that I should look for the problem somewhere else?

About what you said on the horse shoe and the coupler grip, what can I do to improve it? Should I replace the parts with new ones?

Thanks again,

Edited June 23, 2017 by Guest

[SandervG 1,221]

if it is only a few mm, I don't think you need to change your bowden tube. What does the outer surface of your bowden tube look like? Clean or does it has a lot of cuts and scraped surfaces? Besides the length, if the outside is scraped this will also reduce grip. You could try to add some tape on the outside, but this is more of a 'dirty quick fix' than a solid solution. And this would only make sense if your outer diameter seems to have gone thinner. Do you have digital calipers to measure it?

[Elaup 2]

Thanks for your reply! Yes I can measure it. I launched another large part test and it's printing without clogging. The shell looks fine. Only the inner walls are underextruded.

I'll do the checks you suggest after this print. If I remember well the end of the tube is a bit scratched but not really worn.

[Elaup 2]

To follow-up: the printing quality seems to be good in the end, despite the underextrusion I can see during the build-up on the inner walls. I measured the tube end diameter and it's around 6.4 as over the entire length so I assume the issue I had was a bad connection with the coupler.

Thanks again for all the advices!