RE: ATM Testing for fine grinding

[BOB PRABOWO <BOB@bahana.co.id>]

Hi George,

>Could anybody please suggest a good and reliable way to find out if
>fine
>grinding has finished ? (Checking for pits that is and focal length as
>well).

This is how to test the mirror to see if you've finished fine grinding.
Clean and dry the mirror then hold the mirror a few inches above a
newspaper and look through it. When you can read what was written there,
though it was as if you were looking through fog,  the fine grinding is
finish. But to be on the safe side  grind for two or more wets.
To check for pits I used a 10 x magnifier. I think, during the finall
session of fine grinding the pits became harder to be seen because the
mirror became more transparent and the pits become smaller. But you can
try to check for pits with the magnifier. The way I did it, after the
newspaper test, I ground a few more wets to make sure that I get rid of
the large pits left by previous abbrasives. 
Your finest abbrasives will left some pits (small pits) but they'll
disapear when you polish the mirror.

To check the focal length, it's better if you use the sun test. Wet the
mirror, go outside and face the mirror toward the sun. Then, you
reflected the light from the sun to a wall. Move the mirror back and
forth until you get the smallest reflection of the sun. Measure the
distance from the mirror to this reflected spot of light. That's your
focal length.

Good luck,
Bob P. Sumitro
Jakarta, Indonesia

True Victory is Self Victory!
Harmonize yourself with the
Divine Parent Mind -
salvation lives right within
your own body and soul.

-Morihei Ueshiba-



>
>George
>
>