deformed teflon fix, use a bit of bowden

[fluxline 0]

i posted this last month on google groups when in testing, but i thought i'd post here now that i've run with it for a bit. i've only tested this on an UMO, someone else may want to test it on the 2.

 

it seems there are 2 issues with the teflon inserts:

 

UM2: the new glass impregnated one for the um2 which after time has wear from the rubbing of the filament, forming a groove in the side wall of the teflon.

 

UMO: the orignal non-impregnated teflon piece that came with v2 hotend upgrade, which has heat degradation around the entire base where it meets the brass inside the peek. i have printed xt, and similar to abs, it appears over time the heat can degrade the teflon at that brass interface.

 

Issue with umo teflon insert is what i was trying to fix and as we all know, necessity is the mother of invention and my teflon insert needed fixing over the holidays.

 

what i've done to fix the degraded teflon end:

 

i shaved off the bit of deformed teflon insert and then sanded with fine grit to make flat. I think i took off around 1mm, but hard to tell what the original was but this was the measurement from the inside of the peek where it sits. i bored out the inside of some old pfa bowden tube using a 4.5mm bit. sliced off a 1mm section of that tube and that is the gasket. i inserted that into the peek. and then re-assembled the hot end as normal with the teflon insert sitting inside the peek, on top of the bowden gasket. i then heated the hotend without filament and let cool. checked the thumbscrews again and made sure all was secure. inserted filament and printed.

 

i've printed around 60 hours now in total, including about 30 with colorfabb xt at between 240-247C with no problem just took the ahead apart to inspect and the bit a bowden is still good, clean, not smashed. i can post some pictures if needed, but it just like a normal clean peek and a sliced piece of bowden.

 

hopefully this is useful for someone stuck as i was ... or maybe as a way to increase the life of those disposable teflon pieces.

 

[chrisr 18]

Did the piece of bowden tube resist the heat ok?

 

[fluxline 0]

looks just like when i put it in, except for a little indentation where it mated to the brass. just make sure that it is slightly larger than the amount of teflon insert removed, so that it is pressed together when putting the hot end assembly back together.

 

[chrisr 18]

Thanks, I'll try that next time I dismantle the hot end. I'm amazed the bowden material is up for resisting 240 - 247C or so. I'd have expected it to have melted. Interesting discovery! :-)

 

[fluxline 0]

i believe they are just PFA material, teflon, that even under pressure can resist up to around 260C. In the original hot end there was no teflon piece, the bowden was inserted directly into the peek against the brass tube coming up through the alu block.

 

[fluxline 0]

Wow, hero! never has a little gasket been so proud.

In my opinion, I don't think the teflon issues will go away. it's a part under both temperature and mechanical stresses and will need to be replaced. i would prefer to have a teflon insert that is more resistance to mechanical wear and use something cheap like this for thermal protection as a disposable.

i think if you give it a try, make sure the internal diameter matches the teflon insert and brass tubing. since the pfa is a little deformable under temperature load, the internal diameter is going to depend a bit on how much you tighten down the thumb screws.

 

[nigelc 0]

Teflon, supposedly invented for the Space Race, but has always shown problems, even when applied to frying pans and not on re-entry on a space capsule. It burns and deforms.