Direct drive extruder for Wilson or Prusa i3 rework

This is a direct drive extruder that I designed specifically for 1.75mm filament extrusion on my Reprap Wilson.
How to use:

• It will connect to the standard X carriage (also X carriage for the Prusa i3 Rework by eMotionTech) using four M4 x 20mm screws and nuts.
• Uses a MK7 drive gear (probably MK8 too, but I've only been using MK7)
• You will need 3 M3x30mm screws to attach the motor (one is also used to support the hinged lever).
• The Idler bearing is a 624RS bearing, held in place by a M4x20mm screw and locknut.
• For the spring, choose a 1" (uncompressed) spring with decent (~10lbs/in.) tension.
• Through the spring, use a M3 x 50mm screw with a M3 nut going into the slot on the extruder.
• The hot end mount is JHead compatible and will also work with hot ends like the e3d v6. Two M3 x 30mm screws (probably 20mm or longer is ok) with nuts are used to attach the clamp piece to the outer side of the hot end. A fan mount is provided for a 40mm fan, for which you'll need another M3 screw and nut to mount and four M3 screws with nuts to attach the fan.
  Also included is a "key" that you can press over the end of the motor so that you can manually turn the extruder. It only works with D-shaft motors.

There's also an assembly video for this extruder now on YouTube:

https://www.youtube.com/watch?v=z2bXSRLNdbQ

UPDATE Jan 22, 2015 I've altered the extruder body and idler a little bit to add a slot for a second tension spring. This helps keep the idler from pushing more flexible filament off to the side, where it can slip off the drive gear. I've also moved the filament path up a few mm closer to the gear for a similar reason.