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<p>[QUOTE=&quot;Kentucky, post: 1494909, member: 33176&quot;]About rock tumblers.&nbsp; If you use them the other way around, they are called ball mills.&nbsp; When I worked in magnetic recording tape production, ball mills were still used to &quot;grind&quot; the magnetic paint that would be applied to the plastic film.&nbsp; Instead of the &quot;balls&quot; getting smooth from the abrasive powder, smooth balls were used to reduce the size of the chunks in the abrasive powder (which for magnetic tape was gamma iron oxide).&nbsp; I worked for Ampex, and some of our mills used original &quot;balls&quot; which were Normandy Beach flint pebbles.&nbsp; They turned into beautiful polished stones.[/QUOTE]</p><p><br /></p>

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