Re: [ATM] ATM] Pencil Test/Sphere

[Jeff Lowe <lowe@nanotechsys.com>]

atm-request@atmlist.net wrote:

From: michael dodge <michaeldodge9@hotmail.com>
Subject: [ATM] Pencil Test/Sphere
To: <atm@atmlist.net>
Message-ID: <BAY116-W1972F89FDA44ADB48E72C9FC110@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"


Hello, this is my first post on the list!  I am currently grinding my first mirror (8 inch f/6), finished with my first grit (80) and have been grinding with the second (120). I know that I need sphere by the end of this grit size, so I test it with the pencil test mentioned on the stellaphane webpage. everything is wearing evenly except the oustide edge, about 1/4 inch in from the edge. What should I do? grind with the mirror on the bottom or on the top? I would like to fix this problem before I go on with fine grinding what should I do? Any help would be greatly appreciated! On a second note I would like to thank francis o'reilly for the videos on youtube, there great! Thanks for any help!

Hi Michael,
You are not ground out to the edge yet. The quickest way to get there is tool on top center over center 1/3 stroke. Since you are so close, I would not go back to 80 but would continue with the 120 grit you have. This also has the advantage of minimizing the 80 grit pits in the outer zone of the mirror. You may loose a little radius doing it this way, so keep an eye on your sag. 

-- 
Jeff Lowe


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