Update 2015-10-25: added a new version with the thread pitch fixed, and designed to use the threaded E3D bowden coupling as suggested by mkelley. This coupling holds better than the pressfit version and the tube is easier to detach than the metal fittings listed below.
Redesigned to work with a different pneumatic fitting (I didn't like the bowden tube connection being the weakest part of the system and this one holds the tube more securely). The secondary gear is inserted from the outside and held in place with brass heat press threaded inserts from McMaster and M3 screws. Check the filament path, if the filament doesn't pass through cleanly, you might need to drill it out with a 2mm drill bit. I used the printer nozzle to press in the brass inserts. This design should be printable without support material.
Most people will be better off using the mounts provided by Bondtech (http://www.bondtech.se/stl-files/)
Filaments: (full list can be found on thrinter.com)
-- Sainsmart Clear PETG?