RepRap Darwin Y axis bearing clamp

This variation on the Y axis bearing housing allows a 22mm 608Z "sk8er" bearing to be used on the Y axis drive shaft. This means the standard 8mm steel drive rod can be used but without the need to file a flat along its entire length. Alternatively, a threaded rod can be used, but attachment of gears using M8 nuts & washers is left as an exercise to the diligent researcher (I'm looking at you Graeme :).