12 BB ball bearing

thingiverse

This requires 12 steel BBs. The standard size for these is 4.57mm or 0.18 inch. You can print the entire bearing with its cage or if you prefer, separate STL files are available for the races and cage so you can print them in different materials. I did not include a hole through the middle, use your favorite 3D modeling or CAD program to punch whatever size or shape of hole is needed. To assemble the bearing, place the inner race inside the outer one. Push the inner race over to one side, which gives enough space to insert the balls. Evenly distribute the balls and center the inner race. Snap the cage into place on one side, between the balls. Hopefully all 12 BBs can be inserted at once. If not, you might need to modify the design to increase the diameter so there is more space between each ball. Commercial bearings are made using this same procedure but with specialized equipment that shifts the races, inserts and distributes the balls, then snaps in a plastic cage or uses rivets or spot welds a two-piece metal cage.