On Wed, 31 Oct 2007 20:32:08 -0700, Fred the Red Shirt
wrote:

On Oct 26, 2:04 pm, "Roger (K8RI)" wrote:
On Fri, 26 Oct 2007 09:53:04 -0700, Fred the Red Shirt
...
Surface Preparation (cleaning) is extremely important as traces
or organics (from handling( will prevent adhesion of the aluminum.

Texereau recommends final cleaning by electron bombardment
in the vacuum chamber.

Which reminded me, my friend uses that plasma for the final cleaning.
Thats a lot of electronic bombardment. :-))



How big is his vacuum chamber?

What sort of vacuum pump(s) does he use?

The roughing pump is a two stage, dual vane, rotary pump with IIRC a
2.6 Liter capacity. (It's big and heavy any way and uses a 1 HP motor)

The diffusion pump is a 10" Siemens with a 3 stage chimney, but no
cold trap. The cold trap is there but only serves as a baffle without
cooling and appears to stop back gassing. It uses about 100 ml of 704
or 705 fluid (although the pump works well with anything between 50
and 150 ml).


One large enough for a 17.5" mirror is rather non-trivial. Assuming
a 20" diameter cylindrical chamber, the top and bottom would need
to support over 3000 pounds each, if the work is done at sea level.

He has a quartz bell jar that is (again IIRC) about 18"in diameter and
close to 18" tall or a bit more. Ultimate vacuum is probably on the
order of 1.2 or 1.3 X 10^-6 or -7 Torr although it doesn't need to go
that high.

Roger (K8RI)