RE: [PSUBS-MAILIST] Sub as panoramic film platform

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

greg@precisionplastics.com

http://www.precisionplastics.com

P please consider the environment before printing this email

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com
Sent: Tuesday, September 21, 2010 4:24 PM
To: personal_submersibles@psubs.org
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.