Filament stuck

[donmilne 2]

You know it's weird, but I could swear that it's printing better than before. Can't think why, except that I reduced the temp to 220C and tweaked the support (moved it a tad further away).

 

[gr5 2,170]

they seemed to involve clearing a nozzle blockage and completely dismantling the print head

Yeah - well - it may look like lots of text but it only takes a minute to read. There are these sharp metal blades in the "bowden holder" and if you simply pull out the bowden you can scrape off the surface such that next time it isn't secured so well and you start to get these gaps (that you already experienced) where the bowden slowly slips upward and then the PLA can potentiall leak out and you get this inner tube effect that you already got. Each time you remove the bowden it gets worse.

 

[donmilne 2]

Did you check this yet? This would explain why the pla softened enough to create that disk in the first place. Although more likely your bowden just wasn't seated properly.

No, I didn't check this. The circumstances of the original failure was given in my first post. It was a print that came loose from the bed and stuck to the nozzle, hence creating a blockage which I assume allowed heat to propagate back up the filament. Anyway I don't know what you mean by the "third head fan" - there are only 2 obvious fans on my UM2 printhead. I can hear what is probably a third fan somewhere, but I don't see it. Are you familiar with the UM2?

I was careful to check here on how to remove and replace the Bowden tube before I tried it. I didn't simply yank it out and hope for the best. I did try your advice to loosen the print head screws before pushing in the tube and the retainer, but I can't say the grip on the tube seemed any firmer than doing it without that step.

The print came loose because I made the mistake of trying a UM1 profile in KISSlicer, not realizing that it wouldn't include g-codes to heat up the bed.

 

[IRobertI 520]

Look at the head straight on, the fan is "inside" the head, at the back.

 

[gr5 2,170]

I didn't simply yank it out and hope for the best. I did try your advice to loosen the print head screws before pushing in the tube and the retainer, but I can't say the grip on the tube seemed any firmer than doing it without that step.

 

Excellent!

Keep an eye on the gap between the bottom of the bowden and the white teflon part that it touches. If you see any air gap at all then fix that the next time you aren't printing.

 

[donmilne 2]

Just for completeness: I've seen the third fan now (I actually find it more visible looking at the rear of the printhead), and yes it is still working fine.