For my first RepRap build (customized Rostock w/traxxas) when looking for an extruder I decided on the Greg/Wade based Rostock
(Thing 60531 by RichRap) extruder would be the best option given that it was designed for Rostock style printers and had the herringbone gear (I wanted because of the reduced backlash). I also wanted something to be custom and unique to my printer so I enlisted the help of my roommate Erik Scott to help modify RichRap's gear set in Blender. After a half hour of playing around we came up with the Aperture Science logo gear set posted here, please enjoy!
Special thanks to Erik Scott for the Blender work and to Steve Kelly for printing this on his excellent Mendel90!
Not yet tested. I wanted to wait until I finished my Rostock but some friends in my school hackerspace wanted to make their own so I'm releasing it early enjoy!
For these and most herringbone gears to work well its recommended that a high precision well calibrated printer is used. Also I was recommened to print out of PLA instead of ABS because PLA against PLA is less wear than ABS against ABS. Make sure to check you infill setting so that the teeth are solid and not hollow. Refer to the source model for more information!