If you are using old buffs that have shrunk (worn, really), or the
goblet buffs that start smaller, you want more RPMs - you are basically
shooting for a more-or-less fixed surface feet per minute of the buff on
the wood, which varies with diameter and RPM.

It's a good job for the old Shopsmith, if you have an old Shopsmith
hanging around.

Beall suggests 1/3 hp or greater 1725 for the 8" buffs, and 3000 rpm for
the 4" buffs.

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