[2014-07-02] Added a configurable fan duct (preset for a long nozzle).
[2013-09-13] Fixed supports, bottom-width, outlet hole alignment, 25mm motor bolts.
[2013-09-11] Added an optional nozzle stabilizer, fixed the body groove
[2013-08-24] Wider idler hinge, better supports, longer endstop bumper.
Project Home
Gain a little extra height on your Prusa i3 with this simple direct drive extruder. Requires an inverted "mini" x-carriage or you can use the "Universal 24-to-30mm GT2 X-Carriage" http://www.thingiverse.com/thing:135353, also included here.
Refined Design
My one previous attempt at an extruder was the Compact Extraptor http://www.thingiverse.com/thing:120971 and as a conglomeration of extruder and mounting part it's pretty good. But it requires long back-to-front screws and was kind of bulky. With Tweety I started the code over from scratch, centering everything on the filament pinch point, and made it possible to use shorter M3 screws.
Stabilizer
The optional "nozzle stabilizer" was added to limit how far the hot-end may be pulled downward if it collides with an object while the Y bed is moving from front-to-back. This is a weak point of vertical x-carriage setups like the i3. The nozzle acts like a lever, pulling the assembly downwards. For this reason most fatal "head crashes" occur when the bed is moving in the minus-Y direction. By limiting the movement of the hot-end closer to the platform, the stabilizer should improve reliability in cases where a rising overhang or small blob could sabotage a whole print.
Configuration
The SCAD, and the STLs included, are set up for a 2engineers 50:1 geared stepper motor, MK7 filament drive gear, 3mm filament, and a 608 idler bearing. The SCAD is highly parametric, so it should be relatively easy to adapt for your specific motor and dimensional preferences.
Video
See http://www.youtube.com/watch?v=TEPwp8cAwcQ
thinkyhead
