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Posted by Jess Anderson on February 4, 2005, 4:04 pm

Bearing in mind that I don't know much, I *think* acrylic
(that's methyl acrylate sheeting, right?) is very labile to UV,
enough to become cloudy (somewhat orange and even more brittle,
too) in less than one summer's exposure. That might not be a
problem with a front-surface mirror, but certainly would for a
second-surface one.

All along during this thread I've been thinking of mylar film,
which is very lightweight and of course easily shaped against
some suitable substrate (thin plywood or even cardboard). On
the other hand, I haven't a clue how well it tolerates UV, but
I think it's pretty good since people trust their lives to it
in high-altitude long-distance ballooning.

[] Nothing would be more tiresome than eating and drinking if
[] God had not made them a pleasure as well as a necessity.
[] -- Voltaire, 1694-1778
*  Copyright 2005 Jess Anderson
*  www.jessanderson.org  *  anderson@wisc.edu

Posted by Gary on February 5, 2005, 4:58 am
Jess Anderson wrote:

Extruded Acrylic sheet (e.g. Plexiglass) is actually listed as being
quite resistant to degradation in the sun.  It gets the highest rating
in my plastics handbook.

One thing to bear in mind is that all of the plastics have a high
coefficient of thermal expansion.  So, you want to be careful in how
you attach it to a support frame with a low coefficient of expansion
so that it does not buckle  or bow as the mirror changes temperature
and ruin the parabolic shape.

Mylar requires some form of surface treatment for UV protection.  If
you used aluminized mylar, the alum coating would protect the mylar if
its on the sun side.  Not sure how long the alum will retain its shine
in the weather.  One thought would be to cover the "mouth" of the
parabola with a clear film, and then use aluminized mylar for the
mirror -- the film cover would protect the alum from dust etc. and
might also reduce heat loss.

If you have trouble finding a local supplier for the aluminized mylar,
try these guys: http://www.mirrorsheeting.com/
I have used them in the past and been quite satisfied.  They don't
mind taking orders for small quantities.


Posted by Glenn on March 7, 2005, 1:33 pm
 I can answer in an unsc ientific fashion that mylar is pretty durable.
Three (Vancouver BC) winters ago I laminated mylar onto a satellite
dish.  It is modestly  faded but still very reflective, enough so that
it will destroy the satellite feedhorn electronics at the focus in a
very short time.  I have yet to add the hot water pickup to the unit
... :-(  too many projects ...

I used polyester resin (ie fibreglassing stuff) to bond the mylar to the
mesh dish.  It is still well and truly stuck there.  It did create a few
  "thin" spots in the reflector but not too bad ... for a cheapass
experiment, definitely not a prduction technique.

Thanks,  Glenn

Jess Anderson wrote:

Posted by Duane C. Johnson on March 8, 2005, 12:05 pm
 Hi Glenn;

Take a look at the cast aluminum receiver built by my
friend Vigil Vinz. See:

A better way to apply the Mylar is to use axle grease for
the glue. The grease doesn't harden yet is sticky enough
to hold the Mylar. Better yet, The Mylar can relax and
form a very smooth surface.

In a few years, when the Mylar deteriorates, it is easily

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Posted by Gunnar on March 8, 2005, 6:15 pm

It takes a hell of a time downloading your page!
as of this writing 83 items left (after about 3-4 minutes).

Heavy traffic or slow server?


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