I doubt the plastic auger is going to be able to withstand the pressure it will be subjected to. My guess is the teeth will just sheer off.

Sorry, that is just a model.  I forgot to actually state that the parts would be water-jet cut out of steel.  Probably stainless for the screw.  Not sure on the body. That would be about heat transfer and surface roughness.

The plastic parts were just to get a feel for it.

The length is still way short compared to the usual L/D for an extruder.

My printrbot wasn't the greatest at getting the square hole in the screw elements straight- and it wasn't the exact size it was supposed to be, so I had to sand down the square dowel that I was using as a center- so the individual elements don't line up perfectly.

ETA- I did think about getting a low temp element for this plastic model and using wax to test it out at a low temp.

I saw the thread about the alternate screws like the hammer drills and had finger-banged a bunch of them at the local hardware store trying to figure out a way to make it work. 

I then thought about making a screw and even the extruder body out of water jet cut metal.

The screw would be made of alternate vanes differing by set degrees around a square drive.  The degress would change to provide a positive advance of the material.

Here are some screen shots of my TinkerCad (so you understand my level of engineering experience) and 3D printed parts from my Printrbot in blue Tglas.

You can even vary the depth of the screw vanes.  I set these up to fit in at least a pellet depth in the feed section, and then reduce the free volume as melt would happen and then actually have a zero-progression, but mixing section.  Kind of like a real screw on a real extruder.

I really think that could work.

The body is a bit more challenging.  You can water jet cut metal up to a few inches thick.  But it the body would have to be longer and made of parts that would have to be held together.  I put a bolt down either side.

I don't know how much clamping pressure I would need?  I don't have a place for the heater band, but I think a heater cartridge in a hole like the bolt is in, on the top and bottom for dual heating would do it. 

Then it goes into a some step down sections to get to the standard brass nozzle.

Since I have some compression built into the decrease in free volume in the screw, I really don't know what will happen under pressure when running.  The stories about the purge compound and the pressure increases with that causing the brass end gave me pause.

Also not sure about the cost of the water jet (which I picked due to being able to cut thicker extruder body sections).   The screw needs to be from about 1/8 inch stock (IIRC) to get the turns about what looks right.

I think the screw design has some merit.  I just don't know if it can be done with the current size pipe.  Keeping it so that the square stock is strong enough to provide the turning force without torsioning is what I'm not sure of.

I'd also want to keep the screw from rubbing against the body, so controlling that better than I see in my early version Filastruder would be something else to design in.

One way around the tube issue would be to use a bigger standard pipe- but I can't find a bigger standard brass 'plug' or die end.  Something like 30mm or so would be about what I need.

I think all of these are things that could be dealt with and the price of a Filabot is so high that I think there is still room- but then I saw the Welllzoom extruders for $600 and complete lines for $2400.   Not sure if I trust them.  I know someone that has one and they have run it in a commercial lab setting as lab extruder and they have been happy with it.

Is this a viable option for a variation of the Filastruder?