[PSUBS-MAILIST] question

[Alan James via Personal_Submersibles]

Cliff,
I'll paste Alec's email below. But I read his email as saying that annealing after machining  is not necessary on the edges where they are not seen, as the sun is less likely to cause crazing there, and if it did it would have no detrimental effect.An additional thought is to do the final machining with lots of water cooling.
Alan
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

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