Mashup Sliced Wade's Geared Extruder for Makerbot

This is a mashup/redesign of several designs and documents, for me the most useful to undertand Wade's extruder was certainly droftarts' pdf http://www.thingiverse.com/thing:8072 and KurtcCircuit's Sliced Wade's Geared Nema 17 Extruder http://www.thingiverse.com/thing:5548
Wade's original design: http://www.thingiverse.com/thing:1794

Some ideas like the smooth central PTFE contact surfaces are derived from the Makerbot^s plastruder MK5 http://www.thingiverse.com/thing:3290

The steppers