You can build a form for most windshield shapes by bending thin sheets of
plywood over frames cut to shape. Use single sheets of plywood because
joints will show in the finished piece. Use enough frames to prevent the
plywood from sagging between them. Cover the form with felt. Pool table
felt works better than fabric store felt. No grease. Borrow a couple of
propane radiant heaters and mount them about 250mm above the form so that
they can be moved back and forth. Cut the acrylic roughly to shape, a
little longer than finished size so you can clamp it, remove the protective
paper and lay it on the form. Fo not try to clamp it yet. Starting either
side of the high point heat the sheet until the ends start to drop and
slowly move the heaters towards the ends. As you get close to shape the
suspended areas will not be heavy enough to pull down so use some spring
clamps and a strip of wood to bring the ends to the form evenly. Press it
down very gently. Don't force it or you will get an uneven bend. Once
clamped keep the heat going all over the form for a few more minutes to
insure that the acrylic sets to the form but don't let it get so hot that it
flows.

You can do this with acrylic (Plexiglass) but not with polycarbonate
(Lexan). Lexan absorbs water and will form bubbles unless it is carefully
baked for a long time at lower than softening temps to drive off the
moisture.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Linemar2002" wrote in message
. ..

Brian Whatcott a écrit dans le message :
...
On Sun, 21 Nov 2004 21:37:04 -0500, "Linemar2002"
wrote:



1) Make a slim box with a heater you can control with e.g a dimmer
switch.
2) Heat a sheet until it is floppy.
3) Drape over a form covered with smooth felt, optionally greased
while it cools.

Repeat steps 2) and 3) once or twice until you get it right.

Brian Whatcott Altus OK

Thanks for the advice! English is not my native language and I am not
sure
if I understand correctly: if I make a mold from plaster it would have to
be
covered with felt that would have been greased prior to melting the
plexiglass? What kind of grease should I use? I have read somewhere that
bubbles could form in the plexiglass, what would cause this and how do we
avoid this? How thick should the plexiglass be?

Thanks again!

Marcel Trudel
Montreal, Canada