[lylecheatham]

I wouldn't compare it to the screw drive they use on injection molding. Those are for pushing pellets and melted plastic, not for pushing a rod (or strand) of continuous plastic.

This design uses threads on the outside of the filament [1] to grip it with a nut.

The main difference is that the design and manufacture of this system is extremely simple, contrary to what you've said. They use off the shelf 4-40 [2] taps and nuts to create a triangular thread. I would even go as far as to say this is _easier_ to manufacture than hobbed gears.

[1] http://www.sciencedirect.com/science/article/pii/S2214860416... Excerpt for those without access: "in the FastFFF system, this limit is overcome using a rotating nut to drive a threaded filament (Fig. 2c), analogous to a leadscrew linear actuator"

[2] http://www.sciencedirect.com/science/article/pii/S2214860416... Excerpt for those without access: "The ABS filament is cut with a standard 4-40 thread (Craftech Ind.), which has a triangular profile (Fig. S1, Table S1) [10]."