Fun little model, makes a nice sound. 

In the picture I have the model with the diameter 20mm and i printed it with 0.14mm layer-hight but I recommend 0.2mm if you don't want to spend too much time on fine-tuning with supports and reprinting. 

I have added another model with a diameter of 18mm for less thick fingers. If more sizes are needed i can add them. Simply downscaling the model might not work as balls already do not have much wiggle-room.

Print settings:

• max support!! Balls in the middle (as well as middle ring) are floating, if you don't make sure that support infill is at approx. 80% the print will fail because of the balls being printed uneven, make sure that supports are placed in a way so that the bottom part of each ball is not floating (consider using support types like concentric support) 
• 0.2mm layer-height (you can try finer, but the print quality of the bottom balls might suffer if you don't support them well enough)
• might as-well set infill to 100% or even better wall count to 10 or so doesn't really affect print time or material usage, else the infill of the balls will be uneven

After printing some balls will likely be stuck to the ring after removing supports, just wiggle them arround a bit and they should come off without too much force.