Well I did this as an exercise because I suck at booleans. This consists of a cube and two spheres. I know it's not quite centered, but it was just an exercise so perfection wasn't my aim. =D 1) Create sphere. Make positive. 2) Create cube. Shorten to half of sphere's height. Make negative. Group to check effect. 3) Create sphere. Resize to create core. Make positive. 4) Select all. Group.