Re: [ATM] Polishing questions - stop polishing, keep polishing, or go back to fine grinding?

["Jerry" <wa4guu@verizon.net>]

It is probably fully polished.

6 hours can be enough for a 6 inch, but 12 isn't really so much on a first
mirror. With experience you can get more efficient. 

If you have to use a 60X microscope to see these "pits" and they are really
pits, they should polish out.

Just one thing here though.  When you say that you did 15 micron and 25
micron, I hope you don't mean in that order.  Did you finish with 15 micron?

Are you polishing with weight?  Even if you finished with 25 micron, if you
polish efficiently you can polish from there.  I had a friend that polished
after grinding with 30 micron and he would get polished out almost as fast
as I would after grinding to 9 micron. On a small mirror with some weight on
it I would think that even if what you are describing are pits they can be
polished out in a reasonable time. If they were pits that couldn't polish
out fairly easily, they would be easy to see with the naked eye.

My recommendation is put about 5 to 8 pounds of weight on it, or press that
hard as you polish. Make sure you are getting good contact and polish for
another hour and see what it looks like then. When you can work for an hour
and see no change consider it done.

Of course, since I can't see the mirror.... I could be wrong.

I'm interested in your history. It's a big job for a 12 year old... But you
see, you didn't give up, did you?

Jerry


-----Original Message-----
From: David Steinhauer
 
I have some questions regarding my 6" f/5 mirror.  I have spent 12 hours so
far polishing it.  


I have noticed no change for at least the last four hours of polishing.
- The other day I bought a $10,  60x illuminated microscope from Radio 

when I look through the 60x microscope while illuminating the mirror by
focusing sunlight on the surface with my 1" lens, I see hundreds of bright
tiny spots!  I'm pretty certain these are pits.


So, did I not spend enough time in fine grinding?  I did 16 wets of 15
micron grit, and 18 wets of 25 micron 
grit.  

Should I go back to fine grinding, or accept that the pits on the mirror are
probably no worse than the amount of dust that typically will reside on the
mirror surface?  Or is this something that might polish out with a few 
more hours of work?

Thanks in advance.

David Steinhauer
Lynnwood, WA, USA

P.S. If you're interested, here's a few words about my background.
Twenty-one years ago when I was 12 I tried to grind a 6" f/8 and eventually
gave up (I was trying to rough out the curve with a standard
center-over-center stroke.  Needless to say, it took forever!).  I finally
bought Richard Berry's book Build Your Own Telescope when the first edition
came out, and built the 6" German equatorial, using commercial optics.  
They must have thought I was a bit odd building the pier for the mount in
eighth grade shop class.  I took a break from astronomy for many years
(college, married, had three children - no energy for hobbies with a 
baby in the house), but now I'm back, and enjoying amateur astronomy more
than ever.


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