"Peter Dohm" wrote

I am not sure what material is used in the currently offered commercial
assemblies, but it may very well be glass. (As you might guess, I also
don't know what material to use as a mold for glass--much less how to form
the resulting mold.)

You can make the mold out of about anything that will stand the heat. Wood
has been used, and so has plaster of paris, or even dry sheet rock compound
or concrete. The trick is to line the surface that will be touching the
lexan or plexi with felt, or lacking that, an all cotton material like
t-shirts are made of. The plug needs to be perfect, because any defect in
the plug will transfer onto the plastic lens. Caution, if you go with woven
cloth, some of the weave pattern will come through onto the plastic. Not
good for windshields, but probably OK for light lenses.

When you use lexan, you need to put it in a low temp oven, of around 150 (I
think) for several hours to let all of the water slowly evaporate out of it.
That will prevent the bubbles in the plastic.

The plastic (acrylic or plexi) should be mounted in a frame, and clamped
securely around the edges. When you are ready to mold it, bring the
temperature up rather slowly, until you get a nice amount of sag in the
middle. Then you are ready to pull it down onto the plug.

The plug should be mounted on a base that has a support which is at least
smaller than the outside of the plug, and the support should be on a base
that will not tip over as you begin the process of pulling the plastic down
around the plug. It should be held there until it cools, almost to room
temperature. The excess can then be cut off with an abrasive cut off wheel
on a dremmel tool or die grinder.

If there are rather sharp, deep bends, it may be necessary to smooth the
plastic onto the plug as it is being pulled downward. Wear cotton gloves,
with perhaps a thicker pair of gloves under it to keep from burning your
hand. You will need a helper, unless you came outfitted with more than two
hands. g
--
Jim in NC