Printable 608 bearing

This is not a print-in-place bearing. Those are fun and have their uses, but they must necessarily be quite loose. If the bearing is instead assembled from parts it can be much tighter, almost starting to resemble a real bearing... If you are looking for a print-in-place bearing optimized for 3d-printing, check this out: https://www.thingiverse.com/thing:3240362

Parametric model

The stl files included are for a 608 or 8x22x7 bearing, but the FreeCAD model is completely parametric so any size can be set, including the clearance between races and rollers. This model is optimized for small bearings, for larger bearings (say > 32mm diameter) this variant might be better; https://www.thingiverse.com/thing:3576371

Printing

No support. Print the rollers with a brim if you have problems getting them to stick to the bed. Small bearings could have this problem, larger shouldn't. Set 'seam position' to random to make the parts as round as possible. If you have problems with an 'elephant foot', i.e. the first layer sticking out due to being squashed against the plate, then you might need to trim it away from the roller ends and the cage holes so they roll freely inside the cage. Any obvious blobs should be trimmed away from the races and the rollers before assembling. It's a good idea to start with only the rollers without brim to avoid having to reprint everything if they don't stick to the bed. Lowering the perimeter and small perimeters speed really helps with printing small pieces that tend to come loose during printing. Also 'avoid crossing perimeters' (slic3r setting) or similar could help.

Assembling

1. Put the 'jig' inside the outer ring.
2. Put the rollers side by side against the outer ring on top of the 'jig'.
3. Fit the inner ring into the bearing, also against the outer ring.
4. Press the inner ring sideways into it's place in the center of the outer ring
5. Remove the 'jig' and spread out the rollers evenly
6. Put the cage in place
7. Snap the cage top onto the cage 'pillars', one pillar at a time using fingernails or some other fitting object. Make sure that the smooth bottom layer side faces down.

UPDATE 2019-04-28:

Switched to FreeCAD 0.18 and found some errors in the model. New version uploaded.

UPDATE 2019-05-20

I added an stl file with an even tighter version of the same bearing. Try this if the other is still too loose.