Re: ATM Edge Problem

[andydtg@alpha1.phoenix.net]

Re:

>> This morning I cast another aluminum blank and I am going to grind this
>> out using the pyrex tool from the glass version and polish it out on the
>> same lap.
>> 
>> I should end up with a spherical mirror that does not need aluminizing.
>> One presumes that the TCE and surface finish will render it useless but
>> I have never been one to believe what everyone presumes and what is
>> useless in general may just have a use in specific.
>> 
>>
>Well good luck. I tried GRINDING aluminum but did not have much luck.
>It was just to soft and grinding went to slow. I had to machine it
>then finish with fine grinding. Also casting type aluminum does not seem to
>bright to me. Let us know if thing go better for you.

We actually made some flat aluminum mirrors for the Shuttle program, by
grinding with 3000 grit followed by cerium oxide on pitch. These were for
docking aids, in which a video camera looks at a reticle machined into
the reflective mirror surface. The mirrors came out ok but had a hazy
surface because of the crystal structure in the aluminum alloy. The
crystal grains and boundaries differ in hardness & don't polish to the
same depth. We later had these diamond turned, this results in a perfect
surface (looks just like aluminized glass!). Unfortunately, diamond turning
technology is only good to about 1/2 wave in visual wavelengths. I believe
that 1/10 wave is possible is sizes up to 24" but won't come cheap.


Andy Saulietis / DTG Alt-Az-Fp Drive Systems
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax