To: Anthony Stillman ,atm{at}shore.net
From: MLThiebaux 
Reply-To: MLThiebaux 


Somebody reading this thread might have noticed and is wondering why the
formula for ROC I posted Mon, 17 Mar 2003 06:24:51 -0400, namely

>...
>If the width of the feeler gauge is  W, or equivalently if the drill bit >is
loose and can be moved back and forth under the straight edge by the
>total amount W, then  ROC = (D^2-W^2)/8T.  D = mirror diameter, T =
gauge >thickness or bit diameter.
>...

is different in appearance from Anthony Stillman's (Wed, 19 Mar 2003 14:06:29
-0800)

>...
>h = r - offset
>ROC = ((2*r*h) - h^2) / (2*g)
>
>
>where
>
>   ROC   radius of curvature
>     r   radius of the mirror
>     g   diameter of the drill bit
>     h   distance from the mirror edge to drill bit
>offset   distance from mirror center to drill bit
>...

The answer is that the two formulas are algebraically identical.  Take your
pick and get the same ROC.

Martial Thiebaux
Rawdon Hills, Nova Scotia

--- BBBS/NT v4.00 MP