Thanks for the comments.
The eyeball I started with was the 50 mm vent available from many sources, I cut out the center divider and then bored the spherical clear through. After a fair bit of trial and error the size of the dividers was determined, ( I would like to get the acual split ratios; I used for the the cross dividers 25% 50% 75% of the diameter)
I made a cad drawing in 3d to get a set of profiles that would interlock and cut them on a cnc, with a bit of fettling to match up the contact points the core 'eggcrate was a snug fit. The face edges are then dressed to match a spherical profile. the thing is then glued in place.
I am quite please with the result
SteveB