Ok, I have one crazy problem. Let me first explain I'm not a professional engineer. But I have one crazy idea, and I need advice from Hydrostatic or Mechanical engineers for my object to survive in.....are you ready for it....

The CHALLENGER DEEP. Yes, at the bottom of the Marianas Trench!

If you think I'm a total nutjob/insane at this point, you're right. But it's (maybe) not as difficult as you think! Granted, I feel like a fool for asking here, but I know no other place for so many professional engineers who know their stuff.

I'm not an engineer by trade. I'm, let's say, an inventor. I have knowledge on a broad range of subjects, and normally I make very normal stuff. My object is an encapsulated purely mechanical device, spring powered. Not sure how to describe it, but basically, I have moving mechanical parts and gears only, that I want to design to operate at the bottom of the Challenger Deep. Normally this would be a monumental problem to say the least.

Why I'm not totally mad- the device in question is almost entirely a solid object, with very little internal volume. We're talking less volume than a shot of expresso. Not a submarine, a very small device- therefore it should be possible, as there is less area to overcome imploding due to huge hydrostatic pressure of about 108.6 MPa, at around 36,000 ft. deep in the ocean.

Here's where it gets technical, and hopefully fun- most of the device is situated between 2 thick and perfectly mated flat industrial sapphire domed crystals. The internal open volume for the device takes the forms of spherical hollows, in the center of the crystals. The main hollow (75% of the total internal volume) is a spherical cavity of about 1.5 CENTIMETERS in diameter.

Here's where I feel embarrased & lost- I'm not sure how to calculate for implosion due to hydrostatic pressure, or what materials variables come into play to do so. I figure tensile strength of the material is the main point, but maybe that's an amateur mistake? I chose synthetic industrial sapphire for 2 reasons- 1, the device must be transparent. 2, Sapphire is the only material I know of that is clear, chemically inert, and has an extremely high tensile strength. The central cavities to hold the instuments are all spherical for a reason- that is the shape that should resist implosion the best/distribute pressure the most evenly, according to common sense, and studies using glass spheres imploding at depth in the sea to test for hydro-acoustic properties within implosion depth ranges.

I know of the near incompressibility of fluids under high hydrostatic pressure, and normally, that would have solved it- I could just fill the entire thing with gasoline, or something, and be done with it. After all, gasoline was used in the hull of the Trieste for incompressible bouyancy. The problem is, the main hollow of the device must either be gas-filled or ideally be under vacuum- part of the device in that portion uses mechanical movement based on a natural spring that must keep regular motion- that would never work properly in a liquid. This is why I am thinking it should be a vacuum- oxygen at that depth would liquefy under pressure? Something tells me I don't get that part well. Forgive me, I normally design very normal, simple things. This is something I thought up "off the deep end", far outside my normal range.

The idea is, the sapphire has a high enough tensile strength that, given a specific total thickness of the 2 mated crystals, with the sphere situated as half in each, in the center, it should survive imploding due to water pressure, and allow the spring motion to work unimpeded in a very small volume of oxygen or vacuum.

Can anyone shed some light on how I calculate for resisting implosion/material thickness needed here? I have basic engineering calculus under my belt from college and did well (A-), but I'm not a scientist/an experienced engineer. I have experience fabbing with synthetic sapphire and metals at small scale, but I can't find anything remotely helpful to aide me in my design! Any submarine engineers here? Somehow I think they might know what I need to do.

And yes, go ahead and call me crazy, I know how nuts this is! I am only attempting this build because the small internal volumes needed look manageable to me. And I only posted this insane question because this is a forum for mechanical design- so it's a relevant question, and a great challenge at that! Maybe one of you better than I will see the fun in addressing such a design and offer some advice. Finally, forgive me if I reply to anyone late- I live in Japan currently (from the US), and am going to bed at 3am!

Thanks.