This extruder is a derivative of Zach's plastruder and I'm really excited to share it. The main difference is that exchanged the idler wheel with a Delrin plunger. This reduces the overall size of the extruder uses two fewer layers.
Using a plunger allows the force exerted on the filament perpendicular to its direction of travel to be adjusted while the extuder is running. I mounted the electronics along the side, so I can view the teeth on the filament on the way to the thermal barrier and adjust the force to get the tooth depth I like.
With this design, changing the filament takes approximately ten seconds from when the barrel becomes hot enough. The motor can be removed with out disassembling the housing.
There is, however, a flaw in this particular design. The captive nut holding the plunger screw will crack the acrylic if you tighten things too much. In the next version I will have this fixed. This design is also based on a larger diameter timing pulley, so the filament guide is a little off.
See it in action http://www.youtube.com/watch?v=HMjVrmLJvIU