Scaled version of the Ultimate Sphere Gear.
I found the 18 tooth gear did not fit at all when the entire model was scaled 2x. I replaced that gear with a filler piece.
The fillers give places to hold the sphere while spinning the gears. They also reduce the likelihood of getting fingers pinched in the gears.
You will need:
8x 21 tooth c gears.
12x 27 tooth a gears with or w/o spinning detent.
12x plug b.
32x M6x30mm long, Flat Head screws.
I printed all parts in PLA, with 1.2mm shell thickness and 15% rectangular infills.
Also be critical about your first layer and retract settings.
Trimming flash off from around the bottom of a bunch of gears is not fun making. Neither is cleaning blobs out of the teeth of the gears.
If you have cleanly printed gears and the gear engagement is too tight to spin easily, reprint the core at about 101% size. Alternately, place thin shims (shim washers) of equal thickness under all pieces. Shims should be no thicker than needed, to obtain running clearance.