Paste extruder based on the Moineau pump principle.
The pump geometry is based on http://www.thingiverse.com/thing:7958
Should work as a plug-in replacement for a hot plastic extruder in a 3D printer. However, I have NOT used this to actually print anything. I'm just publishing it in case someone else wants to try it out. (I think it's ready for printing a very small pizza without toppings, but beyond that I cannot say.)
Almost everything is parametrized and adjustable from the SCAD file. However, the resulting design should be evaluated to see if it is still sane after adjustment, since not all of the features are automatically calculated. Particularly the flange and driveshaft diameters must be adjusted by hand to match the other measurements.
See it in action: http://youtu.be/OHQiKuQvuEU
Note: obviously it is impossible to build an object from material that flows on it's own - the object would not hold it's shape. So in practice the material has to either be pulled into the extruder by a negative pressure (impossible with PLA printed pump parts) or pushed into the extruder by a positive pressure. In either case the motor axle has to be sealed, or it would either relieve the negative pressure or allow the material to flow up and out from the inlet block.
Print plastic parts. Cut flange seals from thin rubber (I used bicycle inner tube). Assemble with M3 nuts and bolts, adding a NEMA17 stepper motor. Fill inlet tube with material to be extruded and start the stepper motor.
There is a seal retention ring near the motor mount inside the inlet block, so that the motor shaft can be sealed with some kind of a seal. With this done, the inlet tube may be made thinner and a flexible tube connected to it for feeding the extruder from an external pressurized reservoir. (This part is still work in progress.)