From stickoutrock's awesome Eliptical Planetary Gears: a remix that includes a "space-frame" that serves to keep all the gears in place.
The frame is held to the outer gear with clips which enables the frame parts to be easily removed and gears swapped out or readjusted. No glue necessary - and the clips enable the whole thing to be put together and pulled apart many times.
The frame does hide some of the beauty of the gears themselves, but does enable a build all from the same material (ie, no clear acrylic necessary).
Everything (including clips) is sized for 3mm acrylic. Thicker or different materials may require readjustment of clip mechanism.
Pieces clip together very simply - and is easy to unclip if the gears are in the wrong spot.