Re: [ATM] industrial polishing pads?

["Dave McCarter" <dmccarter@sympatico.ca>]

> I think these are the sort of "industrial fast polishing pads" that
> all of the standard "telescope making" texts say are not quite suitable
> for producing a final polish on the optics of an astronomical device,
> but I am interested in trying whether or not they may have some virtue
> as a "prepolishing" material to smooth the texture left by the fine
> abrasive before continuing with a pressed pitch lap to refine the
> surface to true smoothness.

Don't do it!  When applied to the grinding tool to do a polishing session
the pads add considerable thickness to the matched surface, and this changes
and lengthens the radius of curvature of the tool with respect to the
mirror. The result is that the edge of the mirror is polished first and
hard, which turns the edge. Precisely what you don't want.

Pitch does not do this because while warm or cold pressing the pitch
conforms to the surface of the mirror, taking on exactly the same radius of
curvature, so the turned edge does not occur.

Dave
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