As Lobby said, it sounds like you were cutting from the bark to the center
of the log so as to turn end grain bowls. What you need is something to
prevent the log from rolling. I use a c clamp that rests the arm on the band
saw table and prevents rolling. For a 10" diameter log I think a bar clamp
might be more appropriate.

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God bless and safe turning
Darrell Feltmate
Truro, NS Canada