[ATM] Dick Parker's mirror workshop

["Francis J. O'Reilly" <foreilly@bestweb.net>]

Or, good enough isn't.

I had the honor of being invited into the home of an accomplished telescope
maker this morning to join him and about a dozen other men for a morning of
pushing glass and testing mirrors and lenses.

Dick and his lovely wife, Nancy, have a home in Tolland CT. In the
basement, Dick has built one of the most incredible optics shops that I
have ever had the pleasure of entering. The other telescope makers were
polite and friendly, two children were there, both of whom were well
behaved and generally enjoyed the session.

The workshop began at about 9:00 a.m. There are about ten workstations
where various projects were in progress. I decided to finish up an 8" f/6
project that I had started about 12 years ago. It is at the polishing
stage. We removed the old lap from the tool after putting it in the
refrigerator. After introductions and looking around a bit, it was time for
the mandatory class in optics, the subject today? Part two of testing and
the benefits of the null test with an autocollimator (Dick has a very
sophisticated autocollimator)After the excellent class conducted by VCR, I
spent the balance of the day learning Dick's method for making a pitch lap.

Making a pitch lap is more of an art than a science. Dick had a coffee can
of pitch melting on an electric burner. We cleaned the old tool and the
mirror, warmed both the tool and the mirror, built a masking tape dam and
poured the pitch. I had brought several rubber grids and molds, but instead
of using them, we removed the tape from the newly poured lap as soon as it
could stand by itself, splashed cerium oxide on both, created an air
channel and hot pressed the lap. Shortly thereafter I cooled the lap under
running cold water and then trimmed the edges with a single edge razor
blade.

Next, Dick set the lap up on a stand, set up a coffee can of pitch
underneath and a torch next to the lap, got a pair of vice grips in which
he placed a large strip of aluminum and showed me how to melt channels in
the pitch to facilitate the flow of the cerium oxide slurry necessary to
polish the mirror. He then set me loose. When I finished melting the
channels I trimmed the edges of the squares (Alright more like trapeziums)
with a single edge razor blade to assure that there were no high spots. We
then heated the pitch lap in more than tepid and less than scalding (That's
a matter of opinion!) water. The mirror was already in warm water and hot
pressed using a piece of bridal veil. (Obviously from a second wedding as
it was purple) I then ran the lap under cold water again and we used a
pencil with a loop of pipe cleaner on the end to brush beeswax on the lap
(Only one pass per trapezium) and we were done.

I had brought along my 8" f/3.92 mirror that I had made years ago.
Somewhere during the process of making a pitch lap, Dick kindly took some
time out to put it to the test. I was amazed that the autocollimator showed
that I had nailed a sphere dead on nuts! This can only be because I had
made numerous mistakes that had fortuitously canceled each other out. This
evening I went home and took some measurements. The mirror is actually a 7
7/8" therefore the mirror at a radius of curvature of 61.75" approximately
comes out to an f/3.92.

Normally, after a day of working on optics, I feel like I have done the
work of three men, Moe Larry and Curly. Today as I drove home, I reflected
on the mornings events while listening to Johnny Maestro and Lyle Lovett.
This was the most enjoyable and productive telescope time that I have had
in a good many years. I truly owe a debt of gratitude to Dick Parker for
assisting me in the telescope making process with his relentless pursuit of
perfection.





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