Broken PTFE insulator in hotend - Why?

Dear all,

I'm quite new to the reprap community and since one month I successfully built my Prusa Mendel. I can now print more or less correctly but this morning, I had a huge failure of my hot end for the second time (!).

I have bought the hot-end here: [www.thereprapkitstore.co.uk]

And this morning the PTFE insulator just broke and the melted plastic were leaking everywhere. I don't have a picture but I found someone who had the same issue: [www.ppl-pilot.com]ℑ=~/App_Data/UserImages/Image/rrp3.jpg

I have exactly the same setup as in the picture (with the PEEK block and everything). So my question is why my PTFE rod broke? Because it's already the second time it broke and I couldn't find any replacement except buying the whole hot end again.

Any help is really appreciated.

Thanks a lot.

Mathieu

... it's mostly bending of the the thread-start and excess pressure, what's ripping the weakest part off

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Viktor
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Thanks for your answer Viktor.

That's what I thought. For some reason the hot end seems to bend the PTFE rod . Do you know a solution to that or a better hot-end alternative?

Did you screw the PEEK block to the extruder?

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[www.hydraraptor.blogspot.com]

Yep it is completly screwed, with bolts on the top and bottom of the peek block, preventing it to move up or down.

yeah i had the same problem. i think it's just a flaw in the design, since it is a common failure mode. The tension of the PEEK block is hard to get right: too tight, and you compress the ptfe, constricting the filament, but too loose and you stress the thin section by the threading. The ptfe also tends to creep, so my print quality got consistently worse. I had it for a year, which was long enough for better alternatives to be developed.

I went with the J head instead

I also saw this J-Head hot end. It seems really rock-solid compared to the ones using PTFE insulator as a mechanical holder. I'll try one like this to see if I get improvements over my 3 days of printing without failure .

Hello everyone,

I'm posting on this thread cause the exact same failure happened to me. Zittix, could you tell me how you solved your problem? Did you buy another PTFE insulator? Where?

Is there any known solution for this problem?

Thanks.
Pierre



Edited 1 time(s). Last edit at 03/18/2012 03:03PM by Pierre le vrai.

Hi Pierre,

Actually I solved this problem bz completly chaning the hot end I was using. PTFE-based hotend (where the PTFE liner is used as mechanical support) are actually really weak. I am now using a J-head nozzle for several months without any problem! You can buy it from here [hotends.com]

Mathieu

Hi Mathieu,

French? Anyway, thanks for the information, I'm gonna check out this hot end, but just a quick question. I read on the website that for printing PLA, you need to add a fan? Did you do that?
And also does it come with the silicone heat compound?

Thanks

Pierre

Hi Pierre,

Not French, Swiss, but French speaking . Yes, after having bought this new hot end, I added two small 4cm fan on each side (one pulling the other pushing air flow through the nozzle). It works like a charm and prevent the hot end to overheat. Since, I didn't any problem with my hot end/cold end. You can find those 4cm fan pretty cheap on ebay.

I attached a picture of my fan mount, which I find quite good and easy to do.

Hope that helps.

Mathieu

the jhead prints ok without the fan, but i think the issue is that the peek isn't as good an insulator as the ptfe. this causes increased ooze and a higher extrude force.

But it still prints, if you don't want to bother with the fan right now. I've also added some copper wire to mine, sort of like a heat sink. i'll post pictures later tonight.