RE: [PSUBS-MAILIST] Big acrylic dome problem

[<jonw@psubs.org>]

Darek,

The "cheapest" way is not the "best" way.  As someone else stated earlier,
your life, and more importantly the life of a potential passenger depends
upon you getting this right; and getting it right the first time.  The
sperical shape can't just look like a sphere, it has to be a sphere.  That
means an accurate geometrical shape with a constant thickness so it can
safely handle the pressure of water against it.

The "best" way to make a dome is to cast it into a mold that has the exact
proper dimensions for the sphere.  This is not financially feasible for a
one time application.  The second "best" way is to machine it, which for the
size you are intending will also be expensive.  The third "best" way is to
vacuum form the hemisphere into a mold.  The least effective method, is to
"blow" it into shape by compressed gas.

No, it is not impossible to heat 70mm acrylic for forming, but it has to be
done in a specific manner as documented in Stachiw's book.  It doesn't
require extreme temperatures, but the heat-up time and cool-down time is
lengthy.  I'm not trying to hide any info from you, it's just that the info
you need is very detailed and impossible to relay through an email.
Stachiw's book has all the data you need to accomplish what you are seeking
to do, which is why you should purchase it.

Please don't take the "cheap" way on this part of your project.  Trust me,
you don't want your last earthly experience to be the implosion of a
viewport failing underwater.

Jon




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