[ATM] polish time for 13 inch

["Mel Bartels" <mbartels@bbastrodesigns.com>]

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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