Re: [ATM] Ultrathin Project update

[Richard <cnc@cncservo.co.uk>]

Hi Arjan,

Thursday, May 17, 2007, 2:22:24 PM, you wrote:

AtM> Possibly the convex side is not a figure of revolution or it may have
AtM> irregularities.

I think that would be a second order effect at worst. Take the case
where the substrate properties approach that of the glass and the
contact approaches molecular. It is then indistinguishable from a
solid lump of glass with a concave surface.

AtM> You can have a "nearly" perfect rigid support then, but
AtM> enough off to cause sag and print-through.

How can it be "off" ?. The plaster has no voids and is in intimate
contact with the convex surface of the mirror, whatever its shape. The
support has been cast in place to the exact shape of the convex
surface. Thickness of plaster is very much greater than thickness of glass.
Lets say 50mm to 100mm of plaster. Vacuum cast plaster is very strong
and hard and bears little resemblance to air cast plaster.


-- 

Best regards,
  Richard in the UK

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