Bob Engelhardt fired this volley in
:

I guess that you're assuming that if it had slipped, it would have
scored the arbor and you would have noticed. I'm not sure that I would
assume that.

It's academic to me - so what if it slips?

I guess you've never properly installed a stone, or at least not noticed
what's what between the stone and flange washers!

If it had slipped, the paper washers would have been abraded.

(Paper what? You don't use them?)

And if it had slipped, then there's the potential for the stone's
becoming loose on the arbor, which could be dangerous.

Lloyd