This is an extruder designed to be used with 3mm filament in conjunction with a Bowden tube between the extruder and the hot end, to help reduce the mass of the moving print head.
The design objectives were to provide for a way to reduce the lateral loads on the gear reduction output shaft, securely mount the tube to the extruder (and the tube to hot end), expose the hobbed gear as much as possible for inspection and cleaning, keep filament centered as it enters tube and finally, be made from easily accessible parts.
It uses a 5.2 to 1 gear reduction nema 17 stepper motor, a modified compression fitting to solidly hold the PTFE tube in place and Airtripper’s fuel line based tensioner. It mounts on a 20x20mm aluminum extrusion.
This 0.1 version has been working on a delta type printer for approximately 4 months now and has been solid so far. Retraction settings have been the most challenging obstacle, it seems as if every brand of filament acts slightly differently.
Future modifications: eliminating the compression fitting and directly threading the PTFE tube into the filament guide would be first in line. A fast release would be handy. Could be much more compact. Integral filament wiper…
The STLs are here: http://www.thingiverse.com/thing:142977
Instructions are here: http://thefabfor.com/yet-another-bowden-extruder/