Direct-drive hinged extruder for E3D/J-Head hot-end (Prusa i3)

Here is my attempt at designing an extruder for my Prusa i3.

I took some inspiration from different designs to try to make an extruder which is easy to print, compact, easy to clean and has tight guides for the filament (to be able to use flexible materials).

I made a couple of test prints with it and it seems to work fine so far. I haven't tested any challenging materials yet, just PLA.

Here are the components:

* [E3D all metal hot end for 1.75mm filament](http://www.e3d-online.com/ourshop/prod_2781400-E3Dv5-All-metal-HotEnd-175mm-Direct-Extrusion.html). It mounts like a J-Head so a J-Head should fit as well.
* [NEMA17 stepper motor](http://robotdigg.com/product/7/NEMA17-Stepper-Motor-40mm-Long,-1.2A). I am using a 40mm motor but any NEMA17 should work. The back of the motor is mounted on the X carriage and all the extruder parts are mounted to the front of the motor.
* [Mk8 Drive Gear](http://reprap.me/epages/reprap_nu_4149051.sf/en_US/?ObjectPath=/Shops/reprap_nu_4149051/Products/%22MK8%20Drive%20Gear%22). The Idler and filament guide are very tight around the Mk8 gear so other gears will probably not fit without modifications.
* **EDIT: The design is now for a 5x10x4 ball bearing** and not the initial [Yoyo ball bearing](http://dx.com/p/steel-ball-bearing-for-yo-yo-5-x-11-x-5mm-127059) (It is a 5x11x5 bearing grooved to 10mm in the center) The groove helps guide the filament but it should also work with a flat 5x10x4, 5x10x5 or 5x11x5 bearing.
* [50mm…