Herringbone Geared Extruder

This is an attempt to combine various aspects of Adrian's and Wade's extruder drivers. Specifically, It keeps Adrian's extruder clamping system, uses a prime number of teeth for good wear characteristics but uses Wade's hobbed bolt to do the driving.

As the name suggests, the design uses Herringbone gears. This ensures that backlash is substantially reduced, which should result in the extruder requiring slightly less reverse, but more importantly run quieter. The design of the drive gear is s