Re: [ATM] hex mirrors

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

The HxTek mirrors were slumped and fused mirrors rather than cast
mirrors.  AFIK, ev4erybody on the list that is doing lightweight
mirrors seems to be doing the slump and fuse method.  Casting is
a bit more difficult as you need to get the glass to flow frerely
and the refractory materiaals are a bit mor difficult to deal
with, witness the first 200" mirror.
I think that the HexTek mirrors used a 3/8" ffrront and rear
plates in that size of blank and used 1/8" or thinner spacers
between teh ront and back plates.
If you're really going to be casting, make the blocks of air
inside conform to the desired ROC of the finished mirror so that
the front plate is about the same thickness throughout.  The
thicker the mirror from front to back, the more rigid the whole
thing will be.
Also, when going to polish the mirror, dno't pour hot pitch on a
cold mirror or you will surely induce a nasty cracking sound
which will ruin your whole day.  Slowly heat the mirror until the
p9itch melts on the mirror!
Bob May
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