[ATM] the effects of scratches...+

[Jim Burrows]

At 08:26 2007-01-28, Norm Prince wrote:

>So the question is...how bad does a scratch need to be to really effect
>performance?  Is painting out the scratch black a bad idea, or would it
>improve performance?

What a scratch does is to scatter light - probably much less than the 
spider - and next to invisible relative to atmospheric scatter.  If the 
scratch has smooth sides, it might not hurt to paint over it, but to keep 
the acattering area as small as possible, the paint should stay inside the 
scratch.

>Also after an hour and a half of walking around the barrel I
>tried something else...I jigged the blank to the turntable of the much
>unloved "M-o-M" and ground by hand with the turntable spinning.  Wow!
>whoever suggested it THANKYOU...its a great idea on too many levels to
>enumerate. (i think Paul Klien might have suggested it...if not he, well one
>of yall put the notion in my head somehow.)

When I asked Bob Goff (RIP) the usual amateur question, "Do I have to go 
back to fine grind?" - my RC secondary had about 10 microns of surface 
P-V.  He said, "Nah, take about 4 hours of polishing.  Jim, you should get 
a spindle for polishing and figuring..."  So I forked out $500 for a 
pottery wheel for the current refiguring task (P-V this time is a little 
less ~ 3 microns).

         -- Jim Burrows
         -- Seattle N47.4723 W122.3662 (WGS84)