Re: [PSUBS-MAILIST] uniform? acrylic viewport thickness

[Ian Roxborough <irox@ix.netcom.com>]

Hi Gene,

actually, I think you where right the first time. (Phil is right too.)

The technic, if I understand it, is to control the temperature so that
the center of the acrylic sheet is cooler in the center, hense stretches
less in the cetner when blown into a dome.

While this technic would result in a thinner overall dome, it would
also result in apex being closer to the overall thickness of the dome.
When calculating the operational and crush depths, the only thickness
measurement that counts is that of the thinnest part of the dome.
So, even with a thinner overall dome, the thinnest point (normally
the apex) would be thicker than the tradisional blowing technic,
hence this dome would have a deeper rating.

It all sounds nice in theory, but I believe it's going to be
very hard in practice.  Maybe running many simulations on a
computer with different temperature grades.  A jig/harness for
building a viewport dome with this technic would maybe consist
of many temperature sensors (the type that can accurately tell
the temperature from a few inches a way) and heat guns suspended
above the blowing jig.  All this would be hooked up to a computer
which would monitor all the temp sensors and turn the heat guns
on/off to ensure the correct temp grade across the acrylic sheet.

If you make a mistake, then you endup with a unsafe dome, for
example, if it's too cool in the center you'll get a flat spot,
ruining the optics and strength of the dome.  Same again, if
one of the heat guns or temperature sensors isn't accurate or
is miss calculated.  If the temperature grade is wrong, you
could end up with a 'step' (similar to bi-focals) in the dome.
If the walls endup thinner than the apex, then you must take
the thickness measurement for the walls.

And then there is the Jerry D. Stachiw fact.  Make a few
dozen of these new domes and distructively test them to make
sure they are behaving as expected and have no strange issues
when they get close to colapse depth.

Overall, it sounds like too much work just for a little extra
acrylic at the apex of a dome.  But, in theory, it should work,
in practice it might be next to impossible.

Cheers,
  Ian.


On Sun, 27 Feb 2005 04:18:24 EST
HUNTR2@aol.com wrote:

> You are right Phil,
> 
> I was thinking shortly after that post that having the same thickness over 
> the whole surface maybe the same as taking all the steel and strenght of a high 
> rise building and distributing its weight and strenght evenly from top to 
> bottom, making use of materials very inefficient.  The apex of a dome doesn't have 
> near the weight on it that the base of the dome has, because the weight is 
> cumulative, increasing toward the base.  So,  an engineer would PROBABLY tell us 
> that it lowers the overall depth rating significantly by making the thickness 
> equal over the whole surface. 
> 
> Gene
> 
> In a message dated 2/24/2005 11:16:31 AM Central Standard Time, 
> pnuytten@compuserve.com writes:
> Hi, Gene:
>         That would make a larger area thinner, with the same net result,
> no?
> Phil Nuytten
> Hi Phil,
> 
> Question...   If you heat the acrylic evenly with several heat lamps, and 
> leave the center just a LITTLE bit cooler than the rest of the project,  Would 
> the apex of the bubble retain more of it's thickness and result in more even 
> thickness over the whole dome?  This might be accomplished by a ring of lights 
> over the project.
> 
> Gene
> 



************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 311
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************