Why is the slot on the body of a fly-cutter offset from
the centre?

Is it so that the cutting edge itself is brought onto
the line of a diameter?

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On the Chronos fly cutter that I have, the cutting bit
is about 6" long and 1/4" square.

How much should protrude at the sharp end? It seems to
me that if there was more than, say, 1", that there would
be destructive forces tending to bend or to shatter the cutting
bit.

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When using fly cutters and planing bits in hand shapers,
surely as the cut proceeds, the cutting bit will wear and
that therefore you will not end up with a uniformly flat
surface?