From: "Andreas Derwahl" 
To: "'Frank Q'" , "Atm-US
\(E-mail\)" 
Reply-To: "Andreas Derwahl" 


> ### This implies grinding 2 surfaces together to get mating
> surfaces for
> extra good contact.

That might be necessary. I'm sorry I didn't distinguish well between ribbed
mirrors like Richard Schwarz's and solid plate glass glued together to the
required thickness. The latter should be much easier to match to the
necessary precision and a lot easier to aply pressure to.

> ## At these pressures/temps, wouldn't it be easier to cut out the
> appropriately shaped
> pieces of glass, grind and mate them, assemble and slump the
> lot ??? The
> only
> uncertainty here is that slumping temps may not be high
> enough to fuse (ie
> glue)
> the pieces together.

I agree that in order for a gluing method to be an improvement it needs to
be easier to do as slumping and fusing. So anything needing fancy equipment
and expensive materials/chemicals would not be worth doing.

> ### Do not underestimate epoxy. It is amazing stuff. Back in
> 1972 (Yep, 30
> years ago)
> my father, in his enthusiam, epoxied the diagonal to its
> mount. ...

I'm not sure if the bond strenght is the problem with glued mirror blanks.
As I understand it's the change of shape at different temperatures. While
there is probably some deformation to be expected when the mirror is not
equilibrated it should at least have the same shape at different
temperatures when it is at thermal equilibrium. So either you have a glue
that has the same expansion coefficient as the surrounding glass like Mel
suggested, or the glue layer is so thin and strong that it doesn't matter.

Andreas

--- BBBS/NT v4.00 MP