RE: [PSUBS-MAILIST] Sub as panoramic film platform ( viewport flange and lens fit)

That’s true. Jerry lists this style as “another method” instead of approved method.

I once asked him about it and he said that he had tested plate viewports with radial o-ring grooves and had never had a failure. He thought that a properly machined groove on the radial acrylic surface (with radius inside corners) was very dependable and, in fact, less prone to cracking than having grooves in the steel. ASME did not agree but Jerry still included the method in his book.

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 kocpnt tds.net
Sent: Tuesday, September 21, 2010 2:45 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Sub as panoramic film platform ( viewport flange and lens fit)

Hi Brian,

I could be wrong, but I'm almost positive that the standards set out in Staichow's book forbit ANY grooves or notches in acrylic.

Anyway, it's probably prudent to check out.

Best Regards,

Jim K

On Tue, Sep 21, 2010 at 11:22 AM, Brian Cox <ojaivalleybeefarm@dslextreme.com> wrote:

Thanks Dan, My lenses will be 6" in diameter and 1 1/2" thick and my flanges are pretty beefy with 3/4" thick wall and 3/4" seat. I think with care hopfully I won't see any significant distortion after welding. If I end up with some variation with how the lens is flush with the top of the flange I could vary the thickness of the gasket material on the seat to bring the lens up or down. The lens needs to be flush with the top of the flange because the O ring has to get compressed by the outside retaining ring. I will have a V notch on the edge of the lens. The gasket on the seat also will act to seal the water out.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Dan H.
Sent: Tuesday, September 21, 2010 6:07 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Sub as panoramic film platform

Brian,

Your going to find that the cast acrylic is anything but constant in size.  Each lens piece is going to measure a difference in thickness form one side to the other. The material is CAST not extruded.

I was originally planning to machine me viewports to fit the lenses and use O-ring seals. I found that impossible unless I wanted to face the entire lens then polish it back to clear.

Another thought came to mind when I was figuring out how to fit the lens. I was thinking of using a radial seal in a chamfer around the outside of the lens. When I looked at the coefficients of expansion of the steel housing and the acrylic lens, I found that the redial clearance could be quite large in cold water and non existent in the hot sun. An O-ring around the outside of the lens could extrude inward.

After I welded in my viewport frames they went out of round and flat so much that my original idea of a simple O-ring wouldn't work anyway. I didn't have the option of machining after welding.

In the end I machined the lenses with plenty of clearance and laid them in using sekoflex. I decided to stop thinking about thermal expansion and just do what has worked for others in the past.

Acrylic is easy to machine. You'll have no problems. Don't run to fast. Use a positive rake angle on your cutting tool and be prepared to deal with a pile of string flying off the tool. But you should preshrink and post stress relieve your material following a preset procedure. If you don't preshrink and you only post stress relieve your lens may be four or five percent smaller when your finished.

Dan H.

----- Original Message -----

From: Brian Cox

To: personal_submersibles@psubs.org

Sent: Monday, September 20, 2010 6:58 PM

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

Hi Jon,

              The plexiglass is definately going to be a fraction of the cost of the cast acrylic. The reason for this is that I have a few thousandths of an inch differences between the eight viewport frames and I'm concerned that they will each have to be custom machined to fit. I'm hoping that the variation will be small enough so I would be able to just have one lens fit all the viewport frames.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Jon Wallace
Sent: Monday, September 20, 2010 11:28 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Sub as panoramic film platform

Hi Brian,

Acrylic and Plexiglas are one in the same. Given the thickness of 1.5 inches I can't see any financial benefit to prototyping with a low grade Plexiglas which no doubt is going to be very expensive regardless of the lower grade. If it is machining that you want to play with, you might try calling around to see if you can get a small remnant. If it is fit-up that you want to play with, how about using a 1.5 inch Styrofoam panel from Home Depot or Lowes?

Jon

On 9/20/2010 11:20 AM, Brian Cox wrote:

Greg,    I have already machined my viewports and they are just waiting for me to get the acrylic lenses to fit in. I was thinking that I could purchase some regular plexieglass (1 1/2" thick) and machine those so I could play around with how everything is going to fit together. Can you tell me if the machining properties are much different between the cast acrylic and regular "low grade" plexieglass?   I imagine that the cast acrylic would be a denser material so it may machine and polish much differently.   Thanks,