You can easily make 1 sphere in 2 halves them using a diferant material make another sphere to fit over the first. Attach the sphere together witha good epoxy them put them on a 4th axis and machine the desired shape into the outer sphere. You could make the inner sphere lock together for machining then, un screw it after. The outer sphere would have to have a foot on it that would be removed after or act as the base for it to sit on.
I am not sure of the material is that you are using, but lets say the inned sphere is aluminum and the outer sphere is another type of machinable material. You can use a sacraficial material for the inner sphere and make a 2 piece outer sphere and attach it to the inner sphere by heating up the inner sphere and appling a layer of bees wax, then you attach the outer sphere. when it cools it will lock the 2 together for machining. After it is done just warm up the part and it will come apart. The apply the outer and inner to make up the sphere. I hope this makes some sence to you if not just delete it  |