Here's the ZBrush sculpt (more details on its creation are here). It has been decimated down to about 400,000 polygons to make is manageable for RhinoCAM.
Here's the block of walnut. It is about 3" x 4.5" x 8". The tail-stock rests in a 1/8" diameter hole.
Roughing begins using a 3/8" diameter 2 flute end mill. This is pretty rough yet only 0.05" was left for the finishing pass.
The 4th axis is rotated to the other side and roughing continues.
First finish pass done using a 1/8" ball end mill. It is cutting from the face to the back of the head.
Here's the final finish pass using a 1/16" diameter ball end bit. Only in the smallest crevices was any material removed.
Here's the part after the router has finished:
Here's are a few clips of the routing process:
Even with all the technology there's still a need for hand work.
Some sections of tear out need to be sanded/scraped out (above the left eye, at the base of the neck). The back of the ears had some very strange tool marks that needed to be filled (I used a mix of sawdust and polyurethane). And the area where the block was attached needed to be carved away and finished to match the curvature of the head and texture of the hair.
With some finish and a base: