Originally posted by Euphie
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Step 1 - clean and dry
Step 2 - fall through trays of square mesh of varying sizes. Agitating the trays helps them fall through. After long enough, the trays contain only balls with one cross-section between the mesh size of the tray it's in and the one above.
Step 3 - verify sphericity. This is where it's tricky, and requires some development work. Here some ideas:
3a - Manually measure a sample size from each group just to verify they aren't all oblong.
3b - Further sort by mass, and manually measure a small sample size for each group. Lowest mass is likely to have the highest sphericity.
3c - Create a plate with a spiral groove cut into the face of it; ~.60" depth, a ~.35" tool diameter, and full radius. Using the measurement from the mesh tray, set the distance of a flat disc from the bottom of the radius on the spiral plate. Rotate the flat disc to drive balls from one end of the groove to the other (ID to OD). Any ball that doesn't pass through gets cast out. Those that pass through are as spherical as the test setup limits them to exactly.
3d - high-speed laser micrometers with real-time discard by air jets. $$$$
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