This looks pretty cool! Wonder if it can get hot enough for a 1mm nozzle?
Whoa.
…And then a pellet extruder rabbit hole.
There seem to be a few companies at this now. Downside is no retracts, upside is pure material that hasn’t been previously extruded already (better quality).
That would work and fit really well on an mpcnc…
Check out their youtube page. He’s milling parts on an aluminum extrusion mill. Looks like he’s milling the auger as well.
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Nice.
I’m actually thinking about a good way to build such a system for about 3 weeks already so this comes at the right time for me. I would like to give a try to 3D printing steel and stuff like that, using a similar principle to MIM (Metal injection molding).
I can probably get my hands over some MIM material, but it is made out of pellets. So I need to find a good system to go from pellets to a wire… I don’t think this is the perfect solution but it could be a start.
Thanks for the video @Barry 
I want to mount it externally and extrude 1.75mm to feed into my regular system… I wonder how picky it is on pellet size, can I feed it cropped waste filament? Can I run it sideways?
Looks like he has two versions, one for 1-4mm pellets and one for thin strips cut from bottles 0.1-0.5mm x 2-5mm. The difference seems to be the auger.
It wouldn’t come out uniform enough I wouldn’t think. It is hard to get it really round and really even. The big machines have multiple heat zones and a much longer auger to get the pressure more even. Then they go though a few hundred feet of water cooling or an air bearing/cooler… Direct extrusion for large nozzles would be nice but it wouldn’t be really clean layers, and no retract.
I think there is an open source plans for this kind of thing as well.
And the first thing I’d want to feed it… ground scrap prints. 
I think I’ve found a way to do retracts, and basically to print exactly as if it was just a regular printhead.
Just not sure yet how I can manage to build it.
Reversing the screw should reverse the pressure but I am pretty sure longer moves will drool or string. I’m not sure how much gearing that one has but the Titan Areo retracts are limited to 24mm/s on a 16th stepping board because of it’s gears. To much gearing and other issues arise.
A pellet extruder, reject part recycler, would be awesome. I hope one of you tries it!
I wouldn’t do it this way, actually the idea would be to fill some kind of damper reservoir with the pellet extruder, keep this reservoir under slight pressure by continuously extruding, while keeping it at the plastic liquid temperature.
Then you would have some cooling and a regular extruder head after that.
The reservoir would act like a damper, keeping the plastic available while allowing for retracts. While retracting, the plastic filament would just go back to this reservoir and melt again.
The only downside I see is that it will be quite bulky, and probably a bit heavy (2 steppers needed)
Not really sure if my explanation makes any sense, it’s a bit complicated to explain, but I’ll try to build that, it sounds like a fun project.
Like a bowden almost, filament on demand, you will need to sync there outputs somehow. Can’t wait to see what you come up with.