I use a Dremel tool a lot, and always try to work with two hands. One
toward the back of the unit, and my other hand on the thin part,
lightly guiding the front, or keeping it from "kicking" off.
I also try to have the direction of rotation way from me where
possible.
I've experienced exactly what happens to you many times, particularly
when you cut from a flat surface into something with a ridge.
I cut the hardened steel bearing race off of a set of motorcycle forks
in a matter of minutes. Can't say you're lucky this happened, but
you're lucky it didn't go down to the bone.
--
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(dirt bikes, rat bikes, rental car abuse...)