Re: [ATM] mirror grinding

["David Harbour" <scarab2@cox.net>]

Scott,

Oddly enough, in the eighties, when I was doing a lot of mirror work, I was
using Willman-Bell abrasives- they were ASTONISHLY uniform in size, and I
never got any pits i. e., pits above the size of the grit; the grind was
always uniform). But I understand that others do get them. I wish everyone
could have my experience with the very high quality Willman Bell carbo that
I had. I don't know if they are as careful grading, or sifting, or whatever
they do to make it uniform, now, as I have not pushed glass in a long time
(at least through grinding-refiguring, yes). But I was always surprised at
that smooth as a baby's bottom surface I got with Willman Bell's abrasives,
back in the eighties! (Can't explain it). (I was not paid any $$ for this
testimonial from WB).

Davey

----- Original Message ----- 
From: "Scott Ewart" <scott.e@quicksurfer.com>
To: <atm@atmlist.net>
Sent: Tuesday, June 21, 2005 9:46 PM
Subject: Re: [ATM] mirror grinding


>     As long as you're still grinding, there will always be pits.  That's
how
> grinding works, by chipping out tiny pieces of glass.  Only when you
polish
> do the pits disappear.  If you want to get an idea how big the pits should
> be, sprinkle a few grains of the dry grit you're working with at the time
> around the area you're using the magnifier on.  The pits should be about
the
> same size as the grit.
>     Don't worry about using too much magnification.  There's no such
thing.
> If the scratches you see at high magnification are not visible at 5x,
don't
> worry.  They'll polish out quickly.
>
> Scott
>
>
> ----- Original Message ----- 
> From: "Cec & Cris" <ccabar@bigpond.com>
> To: <atm@atmlist.net>
> Sent: Tuesday, June 21, 2005 6:03 AM
> Subject: [ATM] mirror grinding
>
>
> | I,m in the process of grinding out my 250 mm mirror and I'm up to the 12
> micron stage. My 5x Magnifying glass does not let me see more than a
couple
> of pits. I've been on this grit for 20 minutes. I decided to use a 25mm
lens
> upside down and I saw all manner of pits. The more I ground the more
> imperfections I saw. I even saw some scratches that are not visible with
the
> magnifying glass. They don't look anywhere near as deep as some of the
pits.
> I can also clearly count the fingerprint lines on my finger. Have I used
> too a large magnification or will the mirror always have some sort of
> scratch or pit under high magnification. I used a 10x magnifying glass to
> view the mirror on saturday and I still couldn,t see any pits or
scratches.
> This was while I was on the 500 grit. I do not own a 10x Magnifying glass
I
> borowed that one for a few minutes. Can someone let me know please.
> |
> | Regards Cristian
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> |
>
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