This is dissection of a sphere into two identical pieces, which includes a hollow cavity when assembled. This is derived from the same basic OpenSCAD script as my previous Hemi-demi-sphere submission.

Build two copies of Hollowdemisphere.stl.

Watch your first model carefully; it starts with a brief 45-degree overhang from a thin edge. If your printer doesn't use support material then the first 10 layers may need a little tuning.

On Hollowdemisphere.stl the upper half of the model also exhibits an overhang. If this gives you too much trouble, try building the cylinderdemisphere.stl version instead; it eliminates the interior overhang by using a smaller cylindrical cavity at the expense of using more material.