Bowden tube feeder with filament release mechanism  
This is a Bowden tube direct drive filament feeder for 1,75mm filament. (User Kert made a remix for 3mm fillament using a geared stepper over here: http://www.thingiverse.com/thing:306532)
The great thing of this feeder is that it has a quick release mechanic to remove the tension of the filament on the extruder motor. This way you can easily remove en feed filament by hand.  
I've made a complete instruction video how to assemble the feeder and explanation of the inner working mechanics:http://www.youtube.com/watch?v=ZsNm0UfQsyQ
(One mistake in video: the two 45mm M4 bolds should be 50mm)  
Also included is a filament spool holder for extrusion bars  
If you use it, please share a picture!

The Libro-Struder is an original 3d printer extruder created at the Pueblo City-County Library District. It is part of the RepRap Libro project but is a general purpose filament extruder for all your filament-pushing needs. It uses plastic-on-plastic friction forces rather than toothed-gear biting forces to grip and advance a plastic filament. The Libro-Struder is less prone to jamming and slipping than the more common Wade or Bowden-type extruders. It can also be created with fewer specialized parts. The design explores the idea of using taken-apart pop rivets as tiny bushings on shafts. The current model does require a stepper motor that has an orbital gearbox attached. I have had much success with a Nema 17 stepper with a 27:1 gearbox, Part No. 17HS19-1684S-PG27.
Hackers encouraged to print their own gearbox. :-)
Original design by David Hartkop, Technology Trainer PCCLD.
Hardware:
Nema 17 motor, 27:1 gearbox #17HS19-1684S-PG27
4 x M3x8mm screws
Push-in pneumatic fitting for 4mm od nylon tube
18 gage steel…