How much separation should there be

Ok this is going to those that already are printing and designing parts.
What is the tolerance when you design something so that when it is printed it already is together for example if I wanted to design a ball bearing including the ball bearings them selves as one object.

So I would have an outer wall surface and an inner wall surface and then between them several spheres to be the ball bearing so For getting the side of the ball bearing if I have a distance between the two walls say 25mm how much of a gap do I leave when designing the size of the spheres so that they indeed are free moving after printing.

I read of one person build large pieces and then using something that looked like a puzzle piece cut to hook the two larger piece together one side male and the other side female. He made the male side .01mm smaller than the female side and when done he had an extremely solid fit he had to work to get the two pieces together.

Now for spheres in my ball bearing how much smaller should I design them so they actually work well.

I am assuming it is something between .01mm from the total diameter which may be too small but 1mm may be too big.
What is a good starting point.

I assume the extruding print width would have something to do with it as well.

Which begs another question what happens if you design inside the extruded print width meaning that the design has two lines so close together that when the printer prints the two lines they overlap sounds like a mess to me.the print head would simply plow into the previous line already laid down correct or am I missing something.

 

One of the things that really caught my attention was the ability to printed these "impossible" things like the gear sets that are already assembled or planetary gears things that come out "ready-to-go". In your experience with the settings you have for your build table(s) what spacing would you use between the teeth of two intertwined gears so that you end up with two movable pieces instead of one unmovable piece of plastic?