ATM Aluminum Disks

[Del Stanton <sdl20@pacificnet.net>]

About thirty years ago a small company that I was 
working for built a 6" aperture f/8 all aluminum 
Newtonian telescope for one of the large aerospace
firms.  The mirror blank was wrought aluminum, 
7075-T651.  The T651 designation means it is 
tempered and stress relieved.  The finishedm figured
mirror was aluminized (and probably SiO2 over 
coated).

I should think stress relieving would be crucial to 
your aluminum mirror project.  I have real doubts 
about being able to polish a cast aluminum surface 
to sufficient smoothness to be a good reflector
without vacuum deposition of an aluminum film.  
Cast aluminum is notorious for its porosity.  It is 
necessary to vacuum back-fill aluminum castings
with shellac or a similar sealant before they can be 
used for pressure or vacuum vessels.

I think it is an excellent project and hope you will 
report your successes/failures.  It will stretch the
envelope of the ATM community.

Del Stanton  - Burbank, California, USA (Near Los Angeles)

"sdl20@pacificnet.net"  (Lower case "SDL" followed by numeric "20")