Summary

This is a single-plate little and big gear extruder gear replacement set for the Printrbot Wood Extruder. It's working well on my PB Plus.

Instructions

I printed this with 0 extra shells, 100% infill, and it seems quite sturdy and reliable on my Printrbot Plus--in fact, it's extruding right now!

It's a derivative of:
http://www.thingiverse.com/thing:26243
I deepened the hex head hole, to put the hobbed bolt teeth at the right depth. There's a little spare depth for a thin washer between the gear and extruder, so if the gear is a little warped, it will still turn cleanly.
If your extruder is a little goopy, like mine, and it prints interior holes undersized, you may need to drill out the center hole to 5/16 inch, and/or chisel some clearance around the hex head. A sharp 1/4 inch wood chisel works well for this.

Spur gears for Printrbot Wood Extruder