ATM Another Update

["Michael Burr" <mtburr@msn.com>]

Here's another update from my first-mirror project -- an 8" f/6, 7/8ths
plate.

First an anecdote:

A funny thing happened last night. As some have described before, at a
certain point in polishing the action began emitting an ear-piercing
"squeal" -- almost a bird-whistle sound, high-pitched and very loud. It was
the first time I'd heard it, and it caught me off guard. Texereau describes
it as "an anguished squeaking". Anyway the really funny thing was the
_cat's_ reaction. She couldn't seem to localize the sound, and she sat there
at the top of the stairs, looking around with that "hunted" look, her ears
rotating like satellite dishes. Then she began meowling with each squeak,
and finally she slunk off to hide under the bed. It was pretty funny.

So now the update:

A few days ago I did the sunspot test as described on Richard Schwartz's
Starfleet Engineering site, and found that the surface of my mirror wasn't
quite as polished as a comparison surface, a 26 mm plossl eyepiece. I could
just barely focus the sun's disc on the surface of my mirror, whereas with
the eyepiece I could not _quite_ do so. (I must say that despite knowing I
wouldn't cause any damage, I felt very strange trying to burn the surface of
my optics with a magnifying glass.) The test also revealed more pits than I
was able to see with other methods. So it was back to more polishing.

I spent about two hours polishing last night, after doing a warm press the
day before for about three hours with bridal veil between tool and mirror,
and another hour of pressing immediately before beginning the polishing
session.

I think I'm starting to get the hang of polishing. I find that standing up
with the work surface on my kitchen table is just about the most comfortable
and effective position I've found. It seems to prevent most of the ergonomic
difficulties that I've encountered with other configurations, and it allows
me to put my weight on the mirror. This is most necessary at the beginning
of a polishing "wet", just after I've charged the surfaces with CeO and
water (with a few drops of detergent for good measure; it seems to help). If
I apply pressure, I can get back to the same quality of adhesion between
tool and mirror that I had near the end of a "wet" quite quickly. Doing
this, a wet lasts between 5 and 10 minutes. Often I'll just wet the outer
squares with water and keep going.

Despite the wise admonishments of several members, I put the mirror on the
tester to see the surface. I did this for two reasons: 1) I had it on a
friend's tester Saturday night during a Foucault demonstration for our
club's ATM SIG, and I was curious about how the shape might have changed
since then. 2) I just finished building my tester and stand, and I was eager
to use it.

It appears that by putting my hands in line at the center of the tool I have
indeed alleviated the turned-down edge that I was creating when I had my
hands at the edges. Apart from that I can only say that it looks like I have
a very slight hill in the center. I'm not going to worry about it as I have
more polishing to do. But in general I have something very close to a
perfect sphere, and I'm happy with that.

Finally, I trimmed my pitch squares as they were getting pretty close
together. What a mess. Oh well.

Best Regards,
Michael Burr