Thursday, May 14, 2009


No-Lathe Extruder Pops Out

I'm having difficulty stopping the barrel of the no-lathe extruder popping out. As the silicone warms up it seems to lose its grip on the barrel and the latter slowly slips out of the silicone/MDF clamp.

This combined with the extra material called for in the form of silicone tube is bringing me back closer to Forrest's and Nophead's extruder designs with long, thin-walled barrels and some form of heat-sink near the inlet.

Vik :v)

You could 'rough up' the end of the tube to provide a bit more friction: but I've had similar problems with PTFE without a thread.

I ended up using the BfB-style penny washer and some bolts to apply force to keep it in and sealed, especially when warm. However, your barrel is smooth and there's nothing to latch on to.

The penny washer also acts a heatsink, so when I put it at the lower (nozzle) end, too much heat gets conducted away and it's difficult to reach temp.

Whichever way I turned, I found I was coming back towards nophead, BfB and the traditional nozzle...
This has wrecked one of my extruders too.

I recall that you were using a BfB extruder (saw it on photo's). This one has a retainer washer. But maybe that wasn't your 'production' extruder?

I myself used a heatsink instead of a washer and push it against the PEEK barrel. This cools the PEEK a little extra. But I must admit that my extruder still doesn't work satisfactory.
I've been wondering if the extruder barrel design I have, made from 5/32 inch copper tubing, works as well as it does simply because the inside of the tube is very smooth.

I know that Chris and the rest of you have been drilling out bolts and similar to make yours. Could it be that the inside surface of your extruders, because they are drilled rather than extruded across a die, is rougher and that that roughness is meaning that you have to have more thrust to get your polymer to extrude?
>'rough up' the end of the tube

Why not drill a few holes through it, sideways?

That would grab the silicone.

You'd have to make them narrow enough that the silicone doesn't obstruct the barrel, though, which might mean some experimentation.
i do like your idea so far, one thought would be to make the threaded barrale a little longer so that you could still use a nut on the other end before silicone and that would stop it from getting pushed through, i think that is your issue any how.

the other think i would try is a small hose clamp too.

in my head i always wanted to try to drill out a small bolt, but i am un sure how well that would work too.

i need to get enough funds so that i can start building one of these soon.
Forest, I tried variations on your design and had gobs of problems.

I only think yours works because you concentrate the heated area in a very narrow zone.
Indeed! :-D
Yes, reducing the size of the melting zone seems key to making the extruder work smoothly. I've been experimenting with bits of heatsink and hope to make another blog post shortly.

I'm presuming that people can buy, bodge or salvage heatsinks without too much difficulty.

Vik :v)
If you use a dense wood (like oak) instead of mdf, you could skip the silicone entirely and focus on getting a more solid grip with wood, possibly using a setscrew.
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