Re: ATM 3 blobs enough?

[The Silent Observer <silent1@ix.netcom.com>]

Jeff wrote:
> 
> For a 10" diameter, 1" thick mirror, are three blobs of silicon adhesive on
> a plywood mounting disk sufficient, or should I construct a 4, 6 or 9 point
> mirror cell?

I don't have enough experience to give a definitive answer, but I can
contribute one data point: my 8" full thickness mirror (probably about
the same weight as your 10" x 1") stayed on its cell through 4000 miles
of freeway, and 56 miles (two 14 mile round trips) on an unpaved ranch
road, while riding in the middle seat of my mini van on a recent star
party trip from Seattle to New Mexico.

It's mounted on three silicone pads 1" square each, with four 1/8" holes
drilled in each mounting point (aluminum mounting pads) and silicone
forced through the holes.

The first time I mounted it, it came loose under its own weight when
sitting still, because I hadn't adequately cleaned the mount plates and
used only about half the area of each.

I can't, however, comment on mirror flex -- it's not an issue with my
full thickness mirror, so I haven't pursued it.  Others here can tell
you for certain, but I'd suggest using six or nine silicone pads located
to minimize flex as the mirror changes position during telescope
pointing.

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Donald Qualls, aka The Silent Observer           NAR # 70141-SR Insured
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Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.