In article , Greg Menke says...

Greater contact area requiring more force to apply the tool, thus more
deflection?

Exactly. Tools with large contact area, like threading,
form, or cut-off, put extreme requirements on the rigidity
of setup.

I forgot about the lock screw... oops.

It's quite probable that some of the flex that contributed
to the 'inscribed circle' was simply the carriage moving
back under the strain of the cut. Lock it down with the
lock screw to eliminate that.

Jim

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