[PSUBS-MAILIST] Clearances

Fri Dec 20 22:58:28 EST 2024

appreciate the feedback guys!

On Fri, Dec 20, 2024 at 5:49 PM Alec Smyth via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Good point, I agree!
>
>
> On Dec 20, 2024, at 5:48 PM, Alan James via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> 
> Great advice thanks Alec.
> So in Rick's case, where he is machining the side rather than the faces,
> the crazing won't matter.
> Alan
>
> Yahoo Mail: Search, organise, conquer
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> On Sat, 21 Dec 2024 at 11:19 am, Alec Smyth via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:
> 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
>
>
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