Sadly, I had to pull the plug on this attempt. Had multiple problems, the final blow appeared to be a bit slipping or some other z axis problem. The 1/16 ball started milling about 1mm lower than it should have right down the center of the map.
I’m going to start over, reduce some of the detail (roads between towns) and try again with the tapered 1/4 inch shaft bits. At this point I’m going to try and avoid 1/8 shaft bits in the Shapeoko. I have not owned the Shapeoko long enough to draw any definite conclusions other than I’m having bad luck with 1/8 bits slipping.