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Hi David
I would suggest some actions for your very thin mirror : 1- regrind the back of the mirror using another
glass blank 1.5" larger using grit 150. Use TOT and MOT strokes so
that the back goes to a reasonable plane. Be shure that both
disks are fully ground up to the edges (use the sharpie test). This
blank will be used as a perfecly matched support for your mirror while
working on it .
2- Place a thin sheet of rubber foam and a
thin sheet of teflon between mirror and the glass blank . Down to up order
is glass blank, rubber foam , teflon sheet and mirror .
3- Place this sandwich on your machine so that
the mirror can play about 3/4" in any direction and rotates in relation to the
glass blank while strokes are running, the blank can be fixed -
without stress - to the rotating base of the machine.
4- regrind the burger to grit
600.
5- repolish the burger using your machine 1/3
strokes being shure that the mirror is sliping+rotating over the bigger glass in
every stroke of the machine arm.
6- if possible do 5 under water+CeO
mix ...
Ricardo Dunna
>> I would like to
get some input on a mirror that I'm working
on. It was a 20 inch .875 inch thick (at edge) float glass mirror blank purchased from Dan Cassaro to work on as a first time mirror project, in spite of the many warnings that I have read about trying such a bold attempt. I'm figuring it as a f/4.7 parabola. Images from a recent ronchi test (.35 inches outside ROC, 200 line/inch grating, moving source) are included at |