And here is my explanation of how I think it happens. BRPro (and likely Sunfly) blanks have concave faces so the centers of the chips will never touch. Other ceramics (like
Tina no-molds) may have a convex face that bulges in the wrong direction, like this:
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Now, when one or more of these convex chips ends up in a stack, one of three things happen.
1. They all face the same direction and "spoon" - no spin.
2. The convex chips are arranged so the concave faces touch - no spin
3. two convex faces touch - Spin!
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And sometimes I think one chip just has enough of a bulge in the center so that it’s the only contact with other chips.