Update[27.7.2017] Release version, obsolete versions removed, Fusion 360 links added:
-Trispinner http://a360.co/2vMkWzz
-Dualspinner http://a360.co/2h5THwv
-buttons http://a360.co/2h5YQoy

You can spin just gears, or you can spin whole thing and gears will spin with it. Bearing hole tolerance is +0.2mm, don't expect long spin times, especially if you're using low quality gears.Blue one in photo with discarded Chinese gears spins 30 seconds, and gears spin for 10 seconds.

If people are interested I'll clean and release Fusion 360 file, meanwhile, if you want different bearing holes, or bevel-spur version feel free to ask, I'll make and release it.

-all 608 bearing is impossible
-I tried to utilize airsoft bearings as bearings instead of spacers, they have much higher friction than 608 or 606.

Ultimaker

Ultimaker 3

doesn't matter

30% is enough, probably can go lower

For body 20% infill is enough, to ensure buttons' durability print them 100% infil, or at least set wall thickness to 1.5mm or higher.rnrnThe blue one in photos was printed on Ultimaker 2+ normal settings 20% infil 1mm wall thickness normal quality, except layer height 0.15mm with Ultimaker blue PLA