Making bowls from a flat piece of wood with a scroll saw is a hoot.  The rings are cut on a bevel, stacked in reverse order, and glued in this type of clamp.  See photo of the scroll saw bowl book that describes the process and this clamp.

The outside dimensions form a 13" cube.

Time to free up shop space. The long bolts, nuts, and washers are worth the price.

P.S. I might have some other scroll saw bowl accessories stashed away that I'll give you.