Re: ATM Caustic Zone Length

[Mark Cowan <cowanm@open.org>]

Rodger Petersen wrote:

>... The best advice I can give is press a lot, short
> sessions, test a lot. I mean a really short session, say 1 minute.My F
> ratio was 9.5 on a 6 inch so it was close as a sphere. The F5 I recently
> completed only took 12 minutes of actual figuring.

You'll have to work up from those 4.25 inchers someday, Rodger. :)

It's true, though.  Figuring can take virtually no time at all, if you
do it right; or the rest of your life, if you do it wrong.  Experience
helps a lot--but if ya'll screw up, you can always polish it back to a
sphere and try again.  

And when you do test after that 1-10 minute figuring, follow Texereau's
advice about temperature equalization--it makes for a longer job, all
the waiting, but you don't want to try to read a mirror that's still
hot. (Especially if you started with a warmed up mirror and lap.  Others
may disagree, but since polishing goes best when the glass is hot, and
parabolizing is a demented kind of polishing, it goes best that way
too.  Plus it gives you good contact which is *vital*.)

Good luck!
 
--Mark Cowan
<cowanm@open.org>
Salem, OR