Re: [ATM] Grinding tips (was Pencil Test/Sphere)

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

The pencil test does work well but you do have to remember that
the surface is still rather hyperbolic in shape (measuring by
light wav velengths!) but that is nothing to bbe really worried
about here.
You have been doing some rather long strokes to get to the
desired sag. and it is now time to shorten them up and proceed
down through the grits.  The only thing that nneeds to be watche
out for at this time is whether you have still some 80 grit pits
in the surface and the 310 grit stage is where that really needs
to be che ked and you just find three or four pits that look
deeper than the rest and do a wet and see if they disappear.  If
so, you're running normal!  Past this stage, the reflection test
shows really all that needs to be seen for pit size as all of the
big pits have been gotten rid of and all that is left is to get
the pit size down to where you can polish the glass surface.
The difficult work of getting a hole in the glass is now done.
The next is to refine the pit size and this really happens
quickly!
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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