FW: [ATM] Back of my blank

[mlbrown at everstrive.com (mlbrown@everstrive.com)]

If you plan on flexing it into a parabola, it needs to be pretty flat and
wedge-free.  If not, usually it can be left as molded, unless it rocks a
lot in your preferred grinding and polishing setup.  If it is really shiny,
sometimes reflections from the back can confuse testing a bit.  

For this reason, I like to hit it with coarse grit just to rough up the
surface.  Plus, I like the look (purely cosmetic) and I like to think
(completely unsupported by evidence) that a ground back holds silicone glue
(my preferred mounting scheme) better.

But really, you can nearly always leave it just as it is.

If you do grind it, chamfer the back edge.  I've seen chips that started
there and proceeded all the way up the side of a 1" thick blank.

=Matt


Original Message:
-----------------
From: Shane LaPierre atmlist@ct-astronomer.com
Date: Tue, 03 Feb 2004 15:41:31 -0500
To: atm@atmlist.net
Subject: [ATM] Back of my blank


Been a while...  Can somebody just let me know how flat my 
8" 1 1/2" thick blank needs to be?  Should I go ahead and 
grind it flat?  I sure like the polish on it, but I can't 
see myself making it look nice again.

Thanks,
Shane LaPierre
http://www.ct-astronomer.com
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