Our first attempt at routing the marble recesses in a game board resulted in an unacceptable amount of tear-out.

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1-2 Shank

Our first attempt at routing the marble recesses in a game board resulted in an unacceptable amount of tear-out, top photo. After switching from a roundnose bit with a 14 " shank to one with a 12 " shank, the tear-out went away, bottom photo. Why? Thicker shanks flex (and chatter) less during operation.
—from the WOOD® shop