Creating Fidget Spinner 3d Model, have a question

I am making a spinner using these bearings. Or at least this size bearing. As you can see it says 22mm diameter. What size will I want to make the holes in my model for the bearings? 22mm? 23? 21?

Isn’t that a philosophical question?

  • mathematically, the hole must have any diameter 22+ε with ε an infinitesimally small positive value, let’s say something close to zero but not really zero.
  • if the model is intended for rendering, you may want a nodge be visible, so either leave a small gap or create a bevel around the hole.
  • if the model is for 3D printing (or physics simulation), you might consider that a SketchUp circle is a polygon (default 24 sides) and the hole’s inscribed circle must match the spinner’s circumscribed circle for being able to rotate.

But I’m curious like you for other people’s experiences.

.1 mm larger than you need.

Then print and test.

Then adjust.


So much comes down to the use (in this case, you need a nice tight fit) and material (PLA and ABS shrink different amounts), that there is not exact answer… Print and adjust!

Most likely your local library has a copy of Machinery’s Handbook
Therein you’ll find extensive guidance on bearing shaft and housing fits.

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Unstated is whether by “making” you mean 3D printing. If so, you need to take into account the shrinkage of the material as it cools. That may take some experimentation. If you need a precision fit, you should do what foundries do: make the hole just a tad small and ream/bore it to size after printing.

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