U2 and underextrusion problem

[Hero_s 0]

Hi everyone, I've had quite a lot of problems with our U2 now. We've had it for maybe 4-5 years and it has print a lot. Here's the previous post when I first asked about its problems 

 

I ended up replacing the teflon coupler, the bowden tube and the nozzle in september this year and the prints were coming out good, but now they're horrible. From what I see, I know that it is some underextrusion problem, but I don't quite know what to do since all the parts that I thought could be the source of the problem are new. Here's how the prints come out :

 

 

I get the same result with different filament and different gcodes, so that's not the problem. Before every try, I also clean the feeder, but it immediately gets dirty when it prints. I think the problem might be in the print head because, when the material is forwarded, it's not grinded at all. You can see on the picture that it begins to deteriorate when it starts printing.

 

 

Any idea on how to deal with this?

 

Sandrine

[Smithy 1,144]

Have you checked the knurled wheel in the feeder if it is still ok? Normally I would say yes, must be ok, if your filament is so grinded, but just the be sure. If the filament slips a little bit, you get under extrusion.

[Hero_s 0]

Hi, thanks for your answer. Yes, the knurled wheel is ok.

[Smithy 1,144]

Ok, next idea, you wrote after changing the parts it was ok, so maybe you have a clogged nozzle now? This would also explain why your filament is so grinded. Some dirt or dust can be enough to get a clogged nozzle.

 

Try to carefully clean the nozzle and make some hot/cold pulls and try it again. 

[Hero_s 0]

Yes, I also thought about it, but even after cleaning the nozzle the problem remains. Also, when the brim comes out, it's almost ok, so a clogged nozzle doesn't seem to be the problem. 

[Smithy 1,144]

Have you changed something on the software/slicer sider? profiles or other settings?

[Hero_s 0]

No, I use the same software with the same profile for my two other printers and everything works with the others. I tried to switch the exact same file from my U2E+ to this printer. It is a successful print with the U2E+, but fails with the U2 

[Smithy 1,144]

Ok, was just another idea...

hmm, I think I am currently out of ideas 🙂

[Hero_s 0]

Yeah, I've been dealing with this since September and I still haven't found the answer...

[geert_2 557]

I would suggest you disconnect the bowden tube at both ends, and then:

 

- Check the tube is not mounted the wrong way around: the wider opening should be at the feeder.

- Manually heat the nozzle to print temp, and manually insert a piece of filament straight into the nozzle, and extrude: does this go smooth, without too much resistance? To make sure the nozzle is clean, and temp is correct.

- Manually push some filament through the bowden tube, while still disconnected at both ends: does that go smooth without too much resistance?

- Then connect the tube again at the nozzle, and feed manually from the back through the tube, and extrude (heat nozzle). Does this go smooth?

- With the bowden tube still disconnected at the feeder, feeding a piece of filament, and pull on it to see if it easily slips? For example if the internals of the feeder would not apply enough pressure anymore due to wear?

- Some more tests along this line?

 

The idea is to *separately* test all parts of the traject. Probably you have done these already, but maybe you overlooked something? Or maybe something has deteriorated recently?

 

I found that it is often a combination of things that causes underextrusion in my UM2:

- Most important: too tightly wound spools, near the end, especially of old PLA that has become very hard: this causes extreme resistance against unwinding, acting like a strong spring, and it causes very high friction in both the bowden tube and in the teflon coupler and nozzle. My solution here is to manually unwind a bit of filament and wind it in the opposite direction around a skater wheel (diameter 7cm). Then let it roll up on the spool again, but now it has a bending radius of ca. 30...50cm, the same as the bowden tube: this causes no more friction. This alone prevents 95% of underextrusion problems for me.

- Deformed teflon coupler after a few 100 hours of use.

- Kinks or sharp bends in the filament, so it has difficulty passing through the feeder and tube.

- Rare, but has happened: dust picked up by the filament due to static charge, and pulled into the nozzle, causing partial clogs.

 

[Hero_s 0]

Thank you! Even though I did most of those, I'll try again and see what happens! I'll come back to you.

[Hero_s 0]

Hi again Geert_2, I didn't know there was different ends to the bowden tubes, but now it's in a correct position. Good to know. I have tried every single step in your message and everything went as well as you could expect. After that, I still couldn't figure out what was wrong. Since I suspected the print head to be the cause of my problem, I decided to replace the teflon coupler again. Even though it didn't show important signs of use and is still quite new, I guess it was the problem 'cause the printings seem fine for now. 

 

Could it be possible that it worn out faster for some reason? 

 

(thank you very much for your help, so much time for such a little piece... ) 

[geert_2 557]

Mine typically last reasonably long, several hundreds of hours. But if you print at hotter temps or higher speeds (=more pressure), they might wear out faster.

If you have a microscope or good magnifying glass, you could look into it from the bottom and see if the inside is deformed?

 

Or maybe it was a bad batch?

 

[Hero_s 0]

Alright, I haven't touch the temperature/speed settings, so it might be a bad batch... I'll look at it closely. Thanks again.