Re: [CAD_CAM_EDM_DRO] re:re: flat glass

ballendo@... wrote:

> I read what you're writing, but my EYES have SEEN the results of
> glass "flow!?! And as a previous posted reply siad, mine is NOT a
> singular experience!

What measurement data do you have to substantiate your claim that
your eyes have see the results? I have certainly seen a lot of
glass windows that have thicker bottoms than tops, but also vary
so much in the centers that statistics say to ignore the results.

> More to the point of this list and the original idea, I would just
> say that using 1/4 plate glass of such a large area will need
> EXTENSIVE, ADJUSTABLE, support to be reliably flat. Any telescope
> makers wish to respond...?

There is no quarrel with 1'4" glass of any sizeable proportions
needing lots of support. Adjustable is really practical
application of support and should not be avoided, if only because
the earth moves - here in California at least.

I think telescope glass is not anything like window glass. Good
mirrors are made of fused quarts, if you can afford it.
Certainly, soda/lime glass is the pits of quality and if anything
would sag a low melting point glass like the first glasses in
Egypt or West Africa should. I haven't seen any of the
archaeological glasses deform because of gravity.

JerryK

>
> Hope this helps.
>
> Ballendo
>
> >The reference below repeats an old wives tale about glass flowing.
> >The experiments that I'm familiar with have not demonstrated flowing
> >of (common soda-lime)glass at room temperature, even under
> >stress<snip>
>
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