UP Mini extruder gear cooling mod

Summary Complete redesign of the extruder plastic components to allow better cooling of the extruder gear and stepper motor. The original wind barrier will work with these new designs. Adds a cooling vent for the extruder gear and exposes the stepper motor for better radiant cooling. All factory wires are long enough to reposition the circuit board. Uses all original hardware. The small guide with small bearing for the filament that fits over the extruder gear has to be trimmed as in the pictures to allow the cooling vent to work.