Hacking the Casio F-91W to Handle 1000 Psi
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The likely explanation is that heating lowers the surface tension [0] and viscosity of the oil so that it can creep easier between the parts. I also considered heating for a problem where a liquid had to enter very narrow cracks.
What you observe with boiling water though is not solved gases leaving the water but actually water turning into steam. Steam is exactly the same stuff as water, just a lot less dense.
Actually if you increase temperature and pressure enough, there will be a point at which it makes no sense to differentiate between water and steam anymore [1]! Which is a fun thing: you can turn water into steam without boiling it. Raise the temperature and pressure enough while keeping it liquid, reduce temperature while keeping the pressure up and then reduce the pressure as far as you like, as long as it doesn't make the water condensate.
Voilà, steam without boiling!
What is happening there is taking a detour around the critical point instead of crossing the blue line (which is where water boils) in the following graphic[0]:
[0] https://en.wikipedia.org/wiki/Critical_point_(thermodynamics... [1] https://en.wikipedia.org/wiki/Critical_point_(thermodynamics...
There are actual diving watches that are rated for 1km or more. The first image on the Wikipedia page for "diving watch" shows one rated for 3km. Rolex famously attached one of their prototypes to the exterior to the Trieste in 1960, and it survived the trip to the Challenge Deep.
If not, even with a thin layer, I doubt the result will give you a readable display, as, judging from the red color of the display in the end result, there’s air between the glass and the LCD display in these watches.
Casio says the F-91W is only splash resistant, so you shouldn't wear it in the shower:
https://www.casio-europe.com/euro/products/watches/collectio...
If you want one you can wear in the shower try the BD640W or similar:
https://www.casio-europe.com/euro/products/watches/vintage/b...
I would imagine the best case for a seal would be to have equal pressure on both sides.
Since internal gas is compressible it would be easier for water to enter with a pressure differential. Then, because the water would have to be next to the seal with pressurized gas behind it to exit again, the water would probably stay.
Having a non-compressible liquid inside would make the seal work less in most cases.
Why are people wearing watches in the shower?
You get to forgo taking on/off the watch and you get to wash the watch at the same time, instead of wearing a watch with residue sweat etc back on after the shower...
From your question I take it you don't wear your watch when sleeping either?
You can always jiggle the band a little and let water / whatever flow underneath.
I hung a Casio W96H by its folded strap on the first ring of the shower curtain. It’s been this way for at least 7 years.
How long are your showers?
EDIT: Although epoxy makes it a bit difficult to change the battery, depending on how you go about it. Maybe some conformal coating on the PCB + mineral oil.
There's one other good reason to use conformal coating: it has very little change in size when it dries. There are a few spots on the board that would be affected by that, most importantly the load capacitors for the timekeeping fork. Ceramic capacitors have a piezoelectric effect and change shape ever so slightly (they stretch and squash, alternately contracting around their midsection and then expanding). It's not enough to break the solder or the epoxy but if you pot them it changes their apparent capacitance, which will change the frequency of timekeeping. Probably not enough to matter, but still measurable. Large inductors have similar problems and can eventually break loose from epoxy.
I'd suggest a good candidate would be a silicone gel. It can be applied to the watch in liquid form, allowing all air to vacate, then cure into a soft solid once sealed in the watch. It could also be removed relatively easily, if you decided you don't want it in there any more.
The real advantage of an oil filled face is the greatly increased readability of the watch.
Does anyone have any idea what the chemical differences between the two are that affect how they interact with rubber? I’d love to learn more.
Mineral oil, contrary to the remark in TFA, is 100% organic. Unlike olive oil, though, it's saturated. Does that matter? It's not exposed to air, so no. But olive oil goes cloudy when cold.
The watch is unlikely to have latex in it, but quite likely to have silicone parts and seals that might soften in silicone oil.
Thanks for the correction! From what I was reading, olive oil goes rancid (and acidic; but mineral oil does not).
("Organic", outside of agriculture, means "composed of carbon compounds". In practice, that usually means compounded by something alive, because life has been at the carbon for a long, long time.)
Nitrile is commonly used in hydraulics as natural rubber doesn't play nice with hydrocarbons.
https://forum.tz-uk.com/showthread.php?330958-The-Little-Wat...
> "I slightly loosen two screws, to let out a couple of drops of oil (which would allow forming a bubble inside the box)."
I think that’s the idea. Could be wrong.
Pull it back again and see if it still works.
Obviously you need a deep ocean, so check a map first.
You’re probably going to have to go off the continental shelf[1] to get 700m it greater depth.
This will make your plan somewhat less trivial.
The view from my office window includes a fjord more than 500m deep; a couple of hours drive to the south, you can get down to 1,300m/4,000ft or so a few hundred meters from the shore.
Edit: Xylakant beat me to it!
For anyone interested in how this can go wrong, Raising the Dead - a book about scuba diving at its limits - has a passage about a rescue diver repairing his dive computer in the field, re-filling the oil, and noticing that he'd lost a drop or two in the process, with a resulting tiny air bubble...
Is the alarm louder or quieter?
Is the tone any different?
I have no plans for deep sea diving any time soon, however, I do like getting up in the mornings. Would an oil filled Casio help me in this practical regard?
I also wonder about how fragrant the oil could be, if you used some oil based perfume, could the watch that is not waterproof be made to smell nice, if only slightly so, but mitigating the odour of bacteria that accumulate on the back of the watch when tightly worn?
If it's waterproof, it's a killer hack for its simplicity and overall cost.
Unfortunately, that would also destroy the LCD and quite possibly the crystal oscillator (not sure how strong the metal can enclosure of those things are). Battery wouldn't survive it either but you could easily take it out and insert it after the vacuuming.
Filling this with mineral oil might actually reduce rather than increase its pressure withstanding ability.
Hopefully someone does some tests.
Also: why do some watches purposefully leave an air bubble in the watch? Is this an aesthetic choice or is there any benefit/detriment to it?
Here is another detailed liquid-filled watch guide [0], which talks more about handling thermal expansion, where rather than using an air bubble, he opts for some sort of foam ring. Another person recommends Flourinert with foam rather than mineral oil [1].
[0]: https://www.christopherwardforum.com/viewtopic.php?f=5&t=496...
[1]: https://forums.watchuseek.com/f21/liquid-filled-citizen-6540...
What happened with the first attempt?
Does the oil leak out of the buttons when they're pressed?
How about the buzzer? I think it's attached to the back of the watch so shouldn't be affected too much?
Someone mentioned improved readability. I assume underwater that is definitely the case, as you no longer get TIR reflections off the back of the watch-face/internal air boundary at steep angles, but how is readability affected in air?
Found this on Amazon
https://www.amazon.com/BARTON-Watch-Bands-Crimson-Standard/d...
Which ironically aren't a NATO standard, but a UK MoD spec.
This is a genuine 'NATO' issue strap:
https://www.cwcwatch.com/collections/m-o-d-spec/products/cwc...
Seeing a lot of commenters wondering if the seals on the watch will manage to keep water out/oil in. Anyone know if it's possible to replace the o-rings or anything like that?
No confirmation if this works.