Re: [ATM] PLOP and the mirror support.

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Jerry Reddell wrote>
> I have been playing with it to determine how best to modify a commercial
10
> inch mirror cell (all cast aluminum) to improve its support.. While
> experimenting with different support rings, number of supports, and radius
> of support rings I found several surprises. The most notable being the
> dramatic negative affect on the error by adding supports in the area where
> the most droop ( i want to say sag) occurs for a near ideal support. The
> intuitive thought is that the added support would further reduce the
error,
> but instead the error increase by a factor of 10 or more.....

The idea is of course to support the glass as evenly as possible over the
surface - I don't know how you did add those points, but if one
configuration is in decent balance, then adding extra lift where not really
needed will upset the delicate  balance.If you add more support points, you
must see that the load is still well distributed - and if you let Plop do
it, it will.

A cell should have its support evenly spaced radially and tangentially -this
is done nicely in the common 18 point cell (but for the center!) - it is not
done well in the classic 9-point cell, where the 3  explaining why a 6-point
cell usually is better (if you let Plop do it, it will move the 9 points to
one circle with 9 evenly spaced points! Even better in theory but not so
easily implemented in practice).


Considering the sagitta where the glass is lighter but more flexible, Plop
can optimize a solution where the center supports are a little closer to
each other but carry less load per point.

Nils Olof


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