Re: [ATM] Grinding Question, and the color of Pyrex

[<dhkblaszyk@zeelandnet.nl>]

Hi Russel,

Yes I took a rotary grinder by hand to dig the hole in the first place. I
went to about 80% en kept some 20mm from the edge. For accurate measurement
of the desired sag I made a template from some scrap MDF. It turned out to
work just fine. When I started to grind the mirror uniformly smoothed out.
Only the edges needed some more time. All in all it took 4 hours to smoothen
the entire mirror and reach the desired N to about 0,2.
Yes it is my first. So I'm learning along and it fun too. Thank you all for
the support.

Kind regards, Darius Blaszijk


----- Original Message -----
From: "Russell Jocoy" <russjocoy@hotmail.com>
To: <atm@atmlist.net>
Sent: Friday, March 18, 2005 3:03 AM
Subject: [ATM] Grinding Question, and the color of Pyrex


>
>
>     My first reply is to Darius Blaszijk, and his question on
"grinding"...
> Did you grind out the center of your disk with a rotary grinder?? This is
> what I took on your first posting...
>    If this is the case, keep your tool on top for awhile and work to the
> edge. What ever your "SAG"
> turns out to be will be... Never dig a hole in a mirror with a power tool
> unless it is guided by some
> form of radius guide or pendulum.. If you were hand grinding, disregard my
> statements.
>      Tool on top , and different strokes can bring the deep curve back up,
> but if you have ground a
> hole in the middle, it might take  a while........ If this is your first
> mirror don't concern yourself with
> the saggita until you get a spherical surface,  You need to work the curve
> out to the edge..
> Once you do this then measure.. make sure you bevel the outside diameter
of
> your disk..
>
>      Jerry...    The color of Pyrex.... I have had the privledge to have
> many different slabs of Pyrex
> glass pass through my hands. Some of this was large 4 foot by 5 foot by 1
> 5/8" slabs, and some
> scrap cut off's. Some also being 7/8" thick..... I have seen color
> difference in separate pieces, from
> "straw color" to "white color"   The large 1-5/8" slabs were towards the
> yellow side, ( althought
> I had some 10"x 40" cut off's that were noticably white. The 7/8" sheet
that
> I still have, 4'x5',
> is white as can be.   As far as annealing I find no stress in either
color.,
> As far as cutting I have found
> no difference in hardness. My guess is either an imperfection in the
mixing
> process or a chemical
> action at a certain temperature. This is a great question that only Pyrex
> manufacturer's could answer.
>    I see no difference in the material, just the color....    Russ Jocoy
>
>
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