“Volumetric” means that a specified amount of rotations from the motor leads to a predictable and repeatable amount of extruded material. Just as in a filament extruder, you can easily calculate the amount of material extruded per step and control your extrusion pretty nicely. The use of a stepper in the design means you have full compatibility with existing electronics and software. RichRap Universal Paste Extruder is an excellent way to get started with paste extrusion and do small tests with various materials. But as we’ve discovered in our testing, for any serious printing of multiple or larger parts, we need to look for a different approach. One potential way to improve the Syringe Pump (which no one has implemented as far as we know) is to use a fairly small permanent chamber with a plunger (like a syringe), perhaps 5-10cc in volume, that can be quickly refilled from the side. Once the plunger has pushed all the material out of the chamber, printing pauses, the nozzle moves off the print, the plunger retracts, the chamber is refilled from a large capacity pressurized container, and finally it does a small starter extrusion before resuming.
VDX Paste Dispenser 2 photo by Viktor Dirks
RichRap - Universal Paste Extruder photo by RichRap
Davids Paste Extruder
photo by David Mckenzie REPRAPMAGAZINE