Re: [ATM] polish time for 13 inch

["Norm Prince" <princenorman@bellsouth.net>]

Them's some good pointers for us newbs Mel...thanks!

-norm-

----- Original Message ----- 
From: "Mel Bartels" <mbartels@bbastrodesigns.com>
To: <atm@atmlist.net>
Sent: Monday, July 16, 2007 23:22 PM
Subject: [ATM] polish time for 13 inch


> Just wanted to drop a note to keep pushing the concept of effective
> polishing.
>
> I'm working on a 13.2 inch f/3 (41.05 inch focal length) slumped plate 
> glass
> courtesy Richard Schwartz.  I polished out from 9 micron aluminum oxide in 
> 4
> hours with cerium oxide (1:10 dilution) (test is the intense light at edge
> of mirror looking for scatter with magnifying lens) using a modest 
> oversized
> tool (14.5 inch diameter), 55 Gogoltz pitch 1/3 inch thick.  The tool is 3
> inches thick of Applyply plywood with doorskin pancakes on top so as to 
> keep
> the pitch thickness relatively constant from edge to center.
>
> The oversize tool controls turned edge on plate glass mirrors very nicely.
> I never channel except for initial forming; I do micro facet heavily.
>
> I'm now about 1/2 parabolized with 30 minutes of figuring, modifying the
> pitch lap by increasing the micro faceting near the edges to simulate a
> parabolizing or parabolic shape by surface area lap.  For this I use long
> strokes with modest side swing.  This keeps the edge from turning.
>
> So polishing can be quick and effective if you really dig in with slow 
> heavy
> strokes.
>
> Mel Bartels
>
>
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> 


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