Just some quick thoughts:

• You would want your mold material to be VERY carefully chosen. I think it goes without saying that whatever the epoxy cures against it will be PERMANENTLY bonded to. So you need a mold made out of something stiff and good at holding dimensional tolerance, but that you can either wash away (acetone perhaps) or crumble to dust. Either way, you will leave a small amount of it behind on the surface.

• Additionally, any material you use for the mold needs to be able to hold an amazing surface finish for the interior, or else you'll have the same problem these guys with all-metal hot ends do, where they simply cannot polish the interior surface enough.

• Rather than use a centrifuge for casting, a reasonably strong vacuum can be used to pull out the bubbles and properly fill the mold. I use this technique for really thick polyurethane casting and I get some pretty flawless results.

• The epoxy itself is a rather poor thermal insulator, but it really shouldn't be too complicated to put a layer of ceramic paste or something similar should do the job.

I think it is just complicated enough to make mass producing difficult and just expensive/troublesome enough to make me not want to try a one-shot. It's a good thought, though.

for the mould, as I said, this can be printed in ABS, easily dissolved in acetone. and shouldn't leave residue, -though what if it does? the whole point of the thermal insulator is that it doesn't get hot, so that ultimately the hot end can be held in a plastic part, (like the MK4 extruder) or wades extruder etc...

the interior wouldn't be moulded (far too difficult), you'd simply drill out the epoxy through the barrel to ensure alignment after the part was cast.

what makes you say that substances like JBWeld are poor insulators?
http://www.reprap.org/wiki/Thermal_Conductivity

it's twice as good as a material such as granite which is used as a pot stand to insulate counter tops from hot pans all the time.
it's roughly the same as rockwool.

Basically according to that chart, JB weld has a thermal conductivity of around 2x that of peek. so should actually be a pretty good choice for the insulator material.

Completely agree with the mass production point though!
but as I said. for you, in your home this isn't an issue, yes, if you're trying to run a business I can see why this might be a problem!

which goes all the way back to the stainless steel discussion before, where I said, as one guy I can spend days on end in front of my lathe carefully lapping the inside of a barrel, but, as a business plan, putting a few hundred dollars of labour into a part that you can only reasonably expect to sell for less than one hundred is crazy...

the point is the best material for the job, and the best material to do the job economically for a business might not actually be the best thing.

http://www.cotronics.com/vo/cotr/ca_putties.htm

• You would want your mold material to be VERY carefully chosen. I think it goes without saying that whatever the epoxy cures against it will be PERMANENTLY bonded to. So you need a mold made out of something stiff and good at holding dimensional tolerance, but that you can either wash away (acetone perhaps) or crumble to dust. Either way, you will leave a small amount of it behind on the surface.

• Additionally, any material you use for the mold needs to be able to hold an amazing surface finish for the interior, or else you'll have the same problem these guys with all-metal hot ends do, where they simply cannot polish the interior surface enough.

• Rather than use a centrifuge for casting, a reasonably strong vacuum can be used to pull out the bubbles and properly fill the mold. I use this technique for really thick polyurethane casting and I get some pretty flawless results.

• The epoxy itself is a rather poor thermal insulator, but it really shouldn't be too complicated to put a layer of ceramic paste or something similar should do the job.

I think it is just complicated enough to make mass producing difficult and just expensive/troublesome enough to make me not want to try a one-shot. It's a good thought, though.

I can't seem to find any information on the thermal characteristics, (like melting point, if it gasses / what it gasses etc)

It would seem like this should be the ideal stuff to make a hot end from though. I assume a good method would be to start with a threaded rod with a hole drilled through it, (like there currently is).
then an added nozzle (like there currently is)
then set this in a block of epoxy/jb weld material where the final shape is a mould, as a bonus it's be possible to cast a nut inside the insulator meaning that the barrel could be removed without damaging the threads in the thermal barrier, (because the threads aren't in the thermal barrier they are in the nut that are cast into the thermal barrier). (you could even print the mould to create the new insulator!)

It's a lot more involved process to make these though, (making the moulds etc).
you'd probably have to cast them in a centrifuge to make a reliable part without bubbles of pockets.
think if the material cost of a current hot end.

About a dollar of brass, a few dollars of peek, a few cents of PTFE as a liner, - retail price, tens of dollars.

You might end up with an amazing hot end, but I'm not convinced that it'll be possible to mass produce.
not you're replacing the few dollars of peek with a few dollars of epoxy.

But you can print the mould, and print and arm and a counter weight, a pivot etc there is no heat or anything dangerous, so this is a pretty cool project. so even casting in a centrifuge wouldn't be out of the question.

once you're finished with the casting you'll need to run a drill be through the hollow barrel to clear the new insulator material out.

so a reasonably complex process is needed for what I imagine will let you get the best results. -that might make it unprofitable if you plan to/want to sell them.

but all the tooling for this (moulds, and even a centrifuge for the casting) can easily be printed. so as a one off project this would be cool...

but back to the first problem...

what temperatures can the resin in the epoxy handle before it either all out melts, or is soft enough to deform.
what temperature will it start to break down and release gasses at.
what are those gasses?

would be interested to find out of there is any information anywhere about the thermal conductivity of exhaust repair paste.
this stuff is made to handle 600 degree C (and higher) temperatures.
it dries pretty rock hard.

whether it prevents heat transfer enough to be used as a thermal barrier would be a good question.
(also this stuff is really thick, so casting it will get more difficult!)

the hot end that you;re thinking of might be this one?
http://www.soliforum.com/topic/2087/mad … rovements/

Might be a dumb question, but why not make the whole hot end assembly out of metal? Like aluminum.

According to some previous discussions, this is quite doable if the assembly is lengthened to include a big heatsink to insulate heat from the hotend from the rest of the extruder:

http://www.soliforum.com/topic/1829/revised-hot-end/

There was another recent thread that included a pic where someone machined a real nice one, but I couldn't find it.

Looking at the thermal conductivity chart referenced in the above link, has anybody tried epoxy?  Seems like a relatively easy material to mold or machine, especially the putty-like compounds if they would be strong enough.

http://www.usplastic.com/catalog/item.a … rchresults

http://www.plasticsintl.com/peek-unfill … -l-en.html