[ATM] Dumb Question: how to measure a...

["Mutalib Abdallah" <omegatroid@hotmail.com>]

Circle.

Given a circle of glass, how can I measure it to characterize its 
circularity?   Assume I do not know where on the glass is the "center", if, 
in fact a center exists.

The only way I can thing of is to measure the coordinates of a large number 
of edge points, copy the data into a computer file, and then do a curve fit 
to find the circle of best fit (either rectangular or polar coordinates).   
Or maybe a truncated fourier series (which is a least squares best fit).

Another way might be to measure the diameter at many points, but I know that 
there are non-circular forms with constant diameter.

Suppose I was writing a specification-- how would I specify roundness?  Is 
there some way to just measure it directly?

I ask this because a friend is making round looking mirror blanks on a jig 
that geometrically should not work.  I want to measure the error of his 
ways.

Ideas?


_______________________________________________
ATM mailing list http://www.atmlist.net/