Zero Tolerance Ball Bearing

I didn't design this for the purpose of 3D Printing, but it can be done.

There are no gaps between the parts, but you can use these ratios if you want to include metal balls:

Ball diameter is 60.7% of the race thickness (bearing thickness or height, not diameter)
Alternatively, the race is 164.7% of the ball diameter

If you have a 1/2 inch metal ball, the race thickness will be .824 (about 13/16), but I suggest scaling it up slightly to create a clearance gap.