From: edwski@comcast.net
To: atm@atmlist.net Subject: [ATM] A polishing we will go!
Date: Mon, 02 Oct 2006 21:42:11 +0000
Greeting ATMers,
Having made an 8 incher and 10 incher, I wanted to go for the gusto.
Originally I was going to get a pregenerated 16 from Newport. Those plans
got delayed(luckily). A few weeks ago I purchased a ready to polish 18 inch
from James Mulherin at OMI. The mirror arrived very well packed and fine
ground, excellent! Looked too nice to polish. Our local mirror making
group meets at the NCA(National Capital Astronomers) mirror class run by
Guy Brandenburg(a big thank goes to Guy!).
We had a old 12 inch pitch lap. After softening it with hot water, we
pressed it with 100 lbs of weight. Then the journey began. I began
polishing with cerox 1670. On the first night, I only manged to put in 45
minutes of polishing. The center was beginning to polish out. :)
A week later, I cold pressed the lap for 30 minutes and began polishing.
Holy Pitch Lap! It is quite a work out, especially when you start to
squeak. 45 minutes and I needed a break. 15 minutes of cold pressing and
back to polishing. All was great until I heard the most dreaded sound you
can hear while grinding/polishing. @$%&* I had scratched the blank!!. There
are a few, one or two that I don't think will get polished out. The pitch
lap was made on a base of some-sort of poured material, this is ok, but
there were still tiles from grinding under the pitch. GRRRRR. I was back
again this past friday, we switched to another pitch lap, this one is
better. Total actual polishing so far, 3.75 hours. The polish is all the
way to the edge, no hazy areas, just a nice smooth polish. Hard work but
fun. I plan on a total of at least 8 hours of polishing before taking a
look on the test stand.
Until Then, Grind more and Enjoy the Sky
Ed Witkowski
Woodbridge, VA
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