[PSUBS-MAILIST] Clearances

[Alec Smyth via Personal_Submersibles]

Hi friends,

I just got a call from Greg, so took the opportunity to ask him about this
question of whether or not to anneal the front viewport after machining it
to the lower diameter. I was correct about "any time you machine, you
anneal" being the proper thing to do, but he also confirmed that Kittredge
never annealed his viewports (which were all tested to 500'). In his
opinion, given the modest depths we operate at, we're fine without
annealing. But what surprised me was the nature of the downside. He didn't
think machined-but-not-annealed viewports would fail prematurely, but he
said they would craze prematurely with exposed to the sun. What happens is
that the machining heats just a very thin layer of acrylic, at the surface.
When you heat those molecules, they contract 2-3 percent, and that puts
stress between the thin layer of surface molecules and the ones beneath.
The crazing you see when acrylic has been exposed to the sun is cracks
between the surface molecules and those below. If there is built in stress
between those layers, then the UV-induced cracks appear much more easily.

He also reminded me of something else. Rick, when you pot the window, be
sure to wipe off the excess Sikaflex, rather than cut it off with a razor.
If you cut off the excess, there's a high chance of scoring the surface.
That, particularly on the inside face of the window that is going to be
under tension, is far more concerning than not annealing as far as
affecting failure depth.

Best,
Alec

On Thu, Dec 12, 2024 at 4:27 PM Rick Patton via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Thanks Hank, I'll check it out.
>
> Rick
>
> On Wed, Dec 11, 2024 at 12:54 PM hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> Rick,
>> I have a concern about using a sealant for your front port.  You mention
>> that you welded up an o-ring groove and thats why you want to use a
>> sealant.  If you did not have the seat machined after welding and smoothing
>> the weld, then it may be distorted.  Using a sealant to make up for the
>> distortion may be a bad idea.  The sealant is not going to transfer the
>> load evenly to the seat, given the softness.  If that is the case, I would
>> have it machined again, even if it means cutting the frame out.  That
>> solves both problems.  Welding it back in would be a breeze for you.  Cut
>> it out from the inside to avoid burning interior stuff.  I have built a
>> wood bulk head in Gamma to protect the interior when I cut the front off.
>> Hank
>>
>> On Wednesday, December 11, 2024 at 07:15:41 AM MST, Jon Wallace via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>
>> We should perhaps seek some clarification from Greg if he's willing to
>> guide us.  I had a conversation with him about Kittredge annealing and he
>> told me Kittredge never annealed any of his viewports.
>>
>> Stachiw was pretty adamant about annealing in his book.  Like Hank, I do
>> seem to recall some restrictions regarding annealing multiple times
>> although I don't recall if it's a single time or a different schedule as
>> Dan suggested and I don't have my Stachiw book with me right now to check.
>> There is a rather obscure one sentence statement by Stachiw in his book in
>> which he says any annealing is better than none.  This suggests to me that
>> while adhering to the strict annealing schedule is ideal, if it cannot be
>> met benefits will still be derived from a looser schedule.
>>
>> Jon
>>
>>
>>
>> On Tuesday, December 10, 2024 at 11:59:14 PM EST, Alec Smyth via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>
>> Hank, what you're proposing sounds totally logical to me. However, I have
>> asked Greg this very question in the past (whether we really have to anneal
>> a viewport.) I'm not sure what the underlying causality is, but he has
>> enough professional experience in the field that I just take his word for
>> it. "You need to re-anneal it whenever any machining has been done on a
>> viewport." Annealing is pretty straight forward.
>>
>> I'm currently working on forming acrylic headlight covers and windows for
>> an antique car restoration. It's a new skill I'm trying to develop, so
>> fortunately I'm not making anything safety-critical like viewports. But one
>> interesting detail is that Greg strongly recommended annealing even for
>> this, because it'll make the covers and windows less likely to crack (there
>> could be stresses caused by mounting screws or flying pebbles, for
>> instance.) He had two basic points he stressed for the things to last:
>>
>> 1) That not all acrylic was equal. The only one he will use is "cell
>> cast" acrylic, and he warned me emphatically to stay away from the cheap
>> stuff which can be referred to as extruded or "continuous cast." I know
>> this has not been mentioned on this thread, but I bring it up because it
>> seems to be key information.
>> 2) Annealing
>>
>> Next time I speak to him, I'll ask about machining with light passes and
>> coolant.
>>
>> Best,
>> Alec
>>
>>
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20241220/023a34d1/attachment-0001.html>