From: "Jerry" 
To: "'Byron Ader'" ,

Reply-To: "Jerry" 


Much snipped...
**************************
-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net] On Behalf Of Byron
Ader
Sent: Monday, July 07, 2003 11:25 AM To: atm-digest{at}shore.net
Subject: ATM Done Polishing (I believe) now Foucault


a very faint hint of "smoked" glass.

I have seen no real improvement over the surface from the last two hours.

I have a constant "donut" in the middle of my mirror.  I have a 6
inch mirror
and can best describe the location of this "donut" as starting 1
1/2" from the edge of the mirror and forming a complete circle all
around my mirror at this distance.. The mirror indicates the type of
shadowing that would reflect the spherical surface except for the donut
(which is illuminated). Inside the donut is more shadowing that probably is
is consistent with the mirror's spherical shape.

I hope I have described this well.


TIA,
Byron
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I'm not sure you described it well enough or not. It can be difficult to
describe unambiguously what you see in the test.

If I understand what you are saying correctly it sounds to me that you
aren't through polishing.

How much total time have you polished?

Look at the area that you call a donut closely and compare it's polish with
the outer 1 inch and the inner. Are the inner and outer area the smoked
parts? It sounds to me that you may be describing a ring that is polishing
faster than the center and edge. You are saying "permanent donut"
and I take that to mean that it stays in the same place when you move the
knife edge. If the outer and inner areas are polished less than the 50
percent zone that zone can look brighter under the test. When you say that
the donut is "illuminated" do you mean all the way around or just
on one side of the mirror and dark on the other side? The donut has a left
and right side. What is dark on the left should be bright on the right and
vice versa. If it is brighter all around and the outer and inner portion of
the mirror are darker the darker areas are not polished as well as the
donut. If you are looking at a donut the crest or high part should change
position on the mirror with forward and back knife movement. From your
description I believe you are only looking at the reflected light from the
light source and not cutting the beam  at the center of curvature with the
knife.

If you see any area that looks even slightly smokey on a clean dry mirror
it is not polished. If you don't polish it completely it will be very easy
to see when it is aluminized. Usually working MOT the edge will be the last
to polish fully.

I hate to be a pessimist but I think you have a bit of work to do. And If
the 50% zone is polishing faster than the center and the edge you may have
a shape problem that will require fine grinding to make the mirror
spherical.

There will naturally be disagreement among others on the list but just to
suggest some time for guidance, a first time mirror maker polishing a 6
inch by hand should not think they have taken "too long" until
they have polished 15 hours. I have seen one polished fully in 6 hours. If
I had 15 hours in and it wasn't polished out yet I would have to have good
reason to believe that 5 more hours would finish it or else I would go back
to grinding. After you have done a few of them you will know much sooner if
there is a reason that it is not polishing fully and a return to grinding
is required.

Hopefully I have misunderstood you and you just need to polish a few more hours.


Jerry

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