A direct drive NEMA17, bowden, mk8 extruder design that attaches to 15by15 openbeam.
I've had some issues with existing extruder designs, namely that the pushfitting have been pushed through the plastic threads or come out of alignment, causing the filament to jam. Or simply that there was not enough pressure on the idler.
This desing attempts to fix those issues by clamping the pushfitting to an m5 nut and using leveraged tension on the idler.
I also wanted to be able to adjust the idler tension as well as being able to clean the hobbed gear without having to take the extruder apart.
Its a bit fiddly to put together but once assembled it does the job without a hitch!
Edit: I've uploaded a new scad-file which is now parametric in regards to hobbed gear. Just enter the inner diameter of your hobbed gear as per http://reprap.org/wiki/Drive-gear
There is also experimental support for flexible filament guides. I've added selectable guides to the scad-file but I haven't printed them yet!
I printed mine in PLA with 50% infill: rock solid but still flexible enough not to be brittle.
1x M5 threaded, BSP, pushfitting
1x M5 15mm bolt
2x M5 nuts
1x M5 washer
1x 625 bearing
1x M3 15mm bolt
2x M3 25mm bolts
3x M3 nuts
6x M3 8mm bolts
1x spring, 6mm wide by approx. 20mm long.