Re: [ATM] Bevel question

["Bob May" <rmay@nethere.com>]

Not a dumb question at alll!  Measure it anyway you want to.  The
fact is that the reason is to get the pressure from the grit on
the glass away from the edge of the glass.  Even a little 1/32"
reductioon of size ofd the mirror will usually do, except
possibly in the first coarse grit.  Whatr is called in the wood
and metal fabrication inductry as a broken edge.
A full 1/8" diagonal measurement will insure that you have more
than enought ot really make suire that you won't have spalling
off of the edge of the glass, the big reason why it is done.  The
spalled off pieces do an excellent job of cutting you at the most
inopportune time and they do cut deep/!  The spalling happens
when the grit presses near the edge and there is no meat of the
glass to support the pressure.  As a result, the crack in the
glass propagates as the edge pullsaway fromm the rest of the
glass and that drops deep and hopefully towards the side of the
glass.  As a result, you end up with a little sliver of glass,
another nice sharp edge on the mirror blank that is ready to
spall again and again.
Bob May
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