Dual hobbed bolt extruder: no-grinding attempt

This is my attempt to make a better extruder for my big printer. I have a bowden extruder and somethimes the filament has difficult to be extruded.
It uses 2 hobbed bolt to drive the filament.
I have finish to prints all the parts but havent try it yet. Still a WIP concept.
haven't upload the body stl file because it has some errors, that I have fixed removing some parts with a cutter...

update 2014-10-20 upload two version of the main body