After 1 year of no activities on my lathe, I am back.
A sphere of 65 mm with 6 spheres inside in maple.
The mother sphere has 3 mm wall, the other 5 have 2 mm wall and the central sphere is 7.5 mm radius.
The spiral support idea comes from “The Manuel du Tourneur” by L. E. Bergeron, 1816, planche 12, fig. 33.