hot end keeps falling out

Hi all. I am using Wade's extruder and a hot end from makerbot (ptfe). I am having a problem where the heater barrel on the hot end is pushed out of the ptfe barrier. I am running 240 degrees C (abs) and I'd like to maintain a large mass flow rate through the extruder. Does anyone know what I should do about this? Are there better materials for the barrier?

Thanks!

Would switching to a PEEK barrier fix this?

Simply put an M6 nut between the metal washer and the PTFE barrier. That way the washer is holding up the heater barrel instead of the PTFE barrier.

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I don't see how this is supposed to hold the heater barrel in the PTFE barrier. The heater barrel slips out of the PTFE barrier regardless of what is attached to the heater barrel. It has to due with the high heat and high pressure against the PTFE threads. They eventually fail and the heater barrel is pushed out.

I've been building my Mendel for the last 2 weeks, and everything else is working pretty well, except for the heated tip.
I'm having exactly the same problem with it repeatedly getting pushed out.

The original design was the Oak insulator type from Techzone, but I've now switched to the PTFE type and I just can't get it to stay in there.
Last night I tried fastening a hose clamp around the lower end of the PTFE barrier but it still didn't hold.

I've now sourced most of the materials to rebuild the entire heated tip from scratch (in quantities large enough to build 20 of the things). I just couldn't seem to find a compatible thermistor and good nichrome wire.
I stripped some nichrome out of an old hairdryer, but its quite long for the 9 ohm resistance required and its not insulated like the original stuff from Techzone.

Anyone have any tips for sourcing these things? I mean what other field or industry would use similar thermistors and insulated nichrome wire? It'll take another week if I have to order these from overseas.
None of the local electronics suppliers seem to know what I'm talking about when asking for either of these items.

...insulated nichrome wire...?

Try a supply shop for ceramicists. Many Potters use electric kilns, which sometimes need a bit of fixing.

Apropos of nothing, how long a piece of hairdryer-sourced nichrome does it take to get 9 ohms?

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-Sebastien, RepRap.org library gnome.

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Yes, this is a common problem that also occurs using reifsnyderb hybrid PEEK/PFTE thermal barrier.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

The issue is that the PTFE expands faster than the brass.

If you're going to stick with that design and not use one of the newer designs that Adrian uses on his geared extruder, then you should consider using a larger diameter piece of brass with deeper thread.

If you want to use the design that Adrian came up with on a Wades, you need an adapter bracket to attach it to.

Adrians design:
1. Puts the brass OUTSIDE the PTFE, so that the PTFE expands into the brass, not the other way around.
2. Puts a piece of PEEK on the end that holds the brass up into the PTFE, so it can't fall out. The brass has a slightly wider area at the top so this can be done.

Take a look at [reprap.org]

Edited 1 time(s). Last edit at 11/19/2010 03:17AM by Cefiar.

Mendel-parts.com sells a nice hot-end of this type.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Try a supply shop for ceramicists. Many Potters use electric kilns, which sometimes need a bit of fixing.

Note: that stuff is not insulated

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

Hazuki,
you might also look at the thread on glass nozzles. It eliminates the problem of using soft PTFE to hold the hot brass. Although we are still working on the best way to heat the tip and measure the temperature of the plastic.

Mike

Oh I see, you're using a Wade extruder with a MakerBot hot end. Well, you need some sort of support to hold the barrel rather than the PTFE. Put something similar to rhmorrison's photo on. That peek block holds the brass barrel, so the PTFE is not supporting the hot end.

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Nichrome wire? You may want to use a vitreous enamel resistor instead. See Nophead's blog from which this was made.

A smaller resistor works better according to nophead.

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I'm building it with Baling Wire

hazuki - if you are printing with ABS then PEEK will solve your problem. If you are using PLA though you'll need a hybrid (PEEK plus PTFE) like this



and then use a grooved adapter to connect it to your wade.

Rick
MakerGear

jgilmore Wrote:
-------------------------------------------------------
> Nichrome wire? You may want to use a vitreous
> enamel resistor instead. See Nophead's blog from
> which this was made.
>
> A smaller resistor works better according to
> nophead.


I use this resistor for heating: [search.digikey.com]
Here's my setup:
[picasaweb.google.com]
The resistors are cheap and work great. I've got quite a few hours on mine, though I bought a few extra just in case. The one I'm using shows no signs of deteriorating.

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Thanks for the responses guys. Yes, I am using Wade's extruder with a Makerbot hot end. I am extruding ABS plastic. Where can I get this grooved adapter for the Wade extruder? Right now I have the PTFE attached to the Wade with hi temp epoxy and that seems to work fine.

If I switch to the PEEK, do I need the extra support for the heated barrel?

Thanks so much.

I've used a peek/ptfe hybrid for about a month now without issue. Before that, I went through four PTFE only thermal insulators; one of which was only in commission for a few hours.

I am curious about what this is: http://www.makergear.com/products/groovemounts

Is the PEEK Groovemount actually the thermal barrier to which the heater barrel screws into? Does this part have the same dimensions as the Makerbot PTFE thermal barrier?

Yes, you screw the barrel into it. No, it does not have the same dimensions but you can use it in place of the standard PTFE insulator.

If you have more questions either post on the MakerGear Google Group or stop by the MakerGear IRC channel (irc://freenode/makergear).

Rick

Had the same problem when using so high temperatures. The problem is that PFTE loses its mechanical properties at around 250. My solution is to make an extra braket. See link:
[www.nordicreprap.com]