Brian,
I first shrunk my viewports with a higher heating process.
This was before final machining. I probably did have
some thickness shrinking then but I didn't have an exact measurement of the
thickness before hand. When you get your acrylic it won't be exact
thickness anyway. My pieces were all different thicknesses. I don't
remember the exact variations but I'm thinking they varied about .030 thousants
of an inch. They even very from one edge to the other of the same
piece.
I was told that thick acrylic sheets is made by pouring the
liquid acrylic between two sheets of glass and there is always some bulging
of the glass form.
If you need exact thickness you should have your acrylic in
hand before you machine your housings.
Dan H.
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