Unfortunately the amount of shrinkage is
not consistent. And, as I said in my last email, shrinking individual viewports
will create optical distortion in the material that can’t be removed. I
suspect that the reason that some folks end up with viewports that are not flat
enough to seal against an o-ring is because they tried to shrink the discs (and
distorted them) and has little to do with thickness tolerance of the cast sheet.
So what to do? Get a bunch of guys
together, go in on a full sheet of pre-shrunk polycast (that will be very flat
and distortion-free) chop this sheet up into smaller pieces, machine them into viewports,
and then anneal the parts in accordance with the schedule in Stachiws book. No
fuss no muss.
Greg Cottrell
Project Manager
http://www.precisionplastics.com
P please consider the environment before printing
this email
From: owner-
Sent: Tuesday, September 21, 2010
4:24 PM
To:
Subject: Re: [PSUBS-MAILIST] Sub
as panoramic film platform
In a message dated 9/21/2010 9:47:39 A.M.
Eastern Daylight Time, greg@precisionplastics.com writes:
The material only shrinks once.
Is there a percentage of shrinkage for a
given thickness and/or diameter that can be used to "size" a disk so
that after cutting it round, machining the edge, and post work annealing the
correct diameter can be reached ?
Or, stated another way, if the cast
acrylic only shrinks once, can the shrinkage factor be added to the original
cut size so that after annealing the disk, it's diameter fits the ring within
the acceptable tolerances depending on what sealing method is used ?
Frank D.