precision extruder is designed to remove filament backlash and work well with flexible filament. designed to be reliable and robust. filament is precision guided into extruder, stepper driver, and bowden cable (see cut-away images showing filament path). direct drive bowden extruder for 1.75 mm filament. can be used with mk7 or raptor drive gear, 608 bearing, and nema 17 stepper. use 25 mm m3 socket cap screw to mount motor. use cut to length spring such as mcmastercarr pn 9663K180. use push-to-connect fitting mcmastercarr pn 5225K503 with standard m5 nut to secure push-to-connect to chassis. for use with 4 mm OD ptfe tubing. through holes for mounting on 20 mm extrusions using m5 socket head button screw. inspired by many fine bowden extruder examples. thank you open source reprap community. successfully printed and assembled, but yet untested as of 2014-05-04.