Re: [ATM] Mirror stuck on pitch lap

["James Sturtevant" <jhsturte@hotmail.com>]

Jerry wrote:

>Whether the parchment does well may depend on the uniformity its thickness
>and how well the flat sheet can conform to the curve of the mirror. If it
>conforms to fast curves then somewhere the thickness must also change or it
>has to wrinkle. In any case I imagine that the variation of thickness will
>be larger than a few waves of light. Maybe that will press out in a few
>minutes. I would prefer that the prior press has it just right.


The wet parchment is quite flexible and, with a little care, has little 
tendency to wrinkle. Even if a small wrinkle does press a groove into the 
lap, that is really not much different from the random scratch grooves that 
many workers put on a lap. The parchment also has excellent wet strength and 
only very rough and careless handling will tear it.

I haven't done the calculations but, intuitively, the difference between the 
actual mirror surface and the parchment covered surface is just a few 
thousandths of an inch in radius of curvature - a very tiny difference in 
shape that presses out very quickly.

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