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...
If you are comfortable with drilling and tapping this is probably mostly self explanatory.
If you want some help along the way there are instructions at http://thefabfor.com/yet-another-bowden-extruder/.
It has been a few months since I built this one so if I've forgotten something or more help is needed please leave a comment.
If you choose to build one here's what you'll need.
1/4" compression x 1/8" pipe fitting A Watts model with a UPC of 042805445372 works fine
2 - 8 x 16 x 5 ball bearings. Traxxas PN #5118 is a package of 2
2 - 4 x 60mm bolts for tensioner
1 - 5 x 60mm bolt for motor mount pivot
1 - 3 x 40 flathead screw to stabilize idler bearing side to motor side
3 - 3 x 8mm flathead screws to fix motor to extruder
2 - 5 x 20mm flathead screws to fix extruder to printer
1-14mm length of 8mm rod for idler bearing
50mm section of 1/4" inside diameter high pressure fuel line for the tensioner
You will also need a few tools:
Drill press, while not mandatory, makes the job easier. Substitute a drill motor and steady hands if you need to.
1/4" x 20 tap & appropriate drill bit (wikipedia sizing chart calls for an #7 sized bit, 13/64" or even 7/32" will work)
1/4: x 20 die & 1/8" drill bit (the drill bit is used to keep the PTFE tubing from collapsing while cutting the threads)
1/8" pipe tap & 11/32" drill bit (the hole on the stl could also be properly sized prior to printing)