[ATM] Speculation (sic!) on Speculum Mirrors

[artbianconi@blast.net]

When I asked why not make the support structure from the 
same material I was thinking in terms of the metal mirror not a 
glass one.

Your response however, does raise an interesting question. If a 
thin glass mirror is attached to a glass honeycomb built up from 
glass with the same CTe using a non hardening bond (silicone?) 
what would happen to the image over temp changes.

On  at , Unknown wrote:

The consequences of a mismatch in the thermal expansion 
depends on the amount of temperature change and on the 
Young's modulus.  Thermal expansion will develop a stress of 
E/alpha per degree of temperature change.  In a metal ribbed 
structure, wherein the entire structure is a good thermal 
conductor, just assume the thing is all at the same
temperature.   With glass you have no such luxury.

. . . Richard


> [Original Message]
> From: <artbianconi@blast.net>
> To: <atm@atmlist.net>
> Date: 5/25/2004 8:32:57 PM
> Subject: [ATM] Speculum Mirrors
>
> So far I've yet to find the formulation Rosse used to match 
> speculum's alpha.  
>
> Now here's the question.  I can't be sure of the exact alloys I have
> and consequently their alphas.  So if I solder these two metals
> together and their alphas are known to say +- 1 percent and differ
> in the worst way, how bad is it going to be?  Anyone?
>

Art Wrote: 
> I am puzzled:  why don't you simply make the ribs from the same
> material as the mirror? It appears you have access to a foundry.
> Pouring a thin "puddle" on a casting plate would give you as thick
> or thin a wall as you need for cutting out ribs. 
>
> It appears that you poured the mirror blank yourself using the same
> foundry methods. If you did then you are probably familiar with
> investment plaster and lost wax process. If so, then I would ask why
> didn't you mold the ribs at the same time you poured the mirror?
>
> Art Bianconi
>
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