This started off really well, I used 2 spheres at different sizes (in wireframe mode) to judge the correct size, then tried to delete a strip of faces in the outer sphere. I then got pointers in the right direction (realising I was doing my process in an inefficient way), deleting the majority of my outer sphere so I can work on it in halves and then duplicate.
Extruding my model to make the outer sphere appear as if it’s not hollow (then using the front -Z view to line everything up as the extrude was angled) I then extruded the face, to create the “teeth” of the outer sphere. The insert edge loop tool was needed to make sure the teeth wouldn’t be too rounded however I wouldn’t be able to replicate it exactly, so I decided to create 24 segments and seperated my outer sphere so I’d only need to work on 1 segment.
I thought working on the segments in sets of 3’s would be easy, yet ended up having a 2:1 from non-teeth and teeth. Instead opting to do it in sets of 2, duplicating it 12 times and translating it to correct spot (translating it two make 24 segments because I then flipped it for the other half of the sphere.
Jonathan's University Blog 