Re: [ATM] Sharpie test: a little help?

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

Ah, the ol' sharpie test1  This is a test for conformance of the
two surfaces to each other.  Where the black (usual sharpie
color) is ground away, that is where the glass is in contact with
the tool.  If you do long strokes when grinding, you will find
that the edge and center won't go away on the sharpie test.  This
sounds like what you have as a problem for a first pass.  The
jproper stroke for a siz inch mirror is one inch stroke length
from the center in any direction.  This means that the total
stroke length is no more than two inches. Long strokes tend to
dig the center more than the shorter strokes and thus you will
have a ring of roubbed out black, usually at about the  seventy
percent zone or near there.
I'll also note that the coarser grits do tend to make a bigger
hole than the smaller grits so be aware that you will see the
ring appearr first before thee rest of the bblack surface gets
into action.  Use very short strokes when doing the sharpie test
and as a setup for the test.  A noe inch total stroke is a good
thing to do for a few moments when you are planning on doing the
sharpie test as the short strokes do tend to circularize the
surfaces more than a normal stroke.
Bob May
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