I agree with your recommendation of Lexan as superior. However, if one is
willing to heat-soften the acrylic then curved surfaces are possible -- see
the many curvaceous aircraft canopies and windshields. My Cessna's
windscreen is over thirty years old with no cracks. (I didn't say no
leaks.)

Ever see the old Vacu-form (sp?) toy?

What really leads to cracks are "stress raisers," scratches or nicks. It
really pays to polish the edges glossy. Also, use oversized holes and
fender washers so the plexi can squirm and move. Never, ever, use
countersunk fasteners.

Roger

http://home.insightbb.com/~derbyrm

"Bob" wrote in message
ups.com...

snip

Just finished replacing six 25 year old acrylic Fuller Brush 7"x15"
port lights. The all leaked and were cracked. Why? the house has a
curve to it. So when port started to leak PO cinched them down and they
cracked. Acrylic can not take much of a curve.

Replaced with 3/8" polycarb/Lexan through bolted with 316L ss 1/4"
machine screws. Used a 1/8" 316 trim ring inside and out as a "washer."
Absolutely bullet proof. Lexan bends without cracking.

If your house has a curve do NOT use acrylics/Plexiglas. It will crack,
if not when drilling it, later from stress from the curve of the
house.

When you go the lexan route can not use 5200 like sealants. I used a
Dow Corning product; 791 I think.

Bob