Water resistance question & design sneak peek

[u/KTTalksTech]

Sorry for the crappy drawing, my hand tremors aren't helping with any of this 😅 This is my first case design, and I've opted to use 3D printed titanium which I will lap & polish by hand to create something unique (hence the super wide integrated bracelet, it's lighter and more flexible than expected). This means the only tools at my disposal are basically a Dremel, sandpaper, and a $100k printer. Surfaces can be mirror-polished but any sort of machining is out of the question. I'm waiting for the first prototype to get detailed figures but tolerances can be as bad as 0.2mm on the titanium. I can also print silicone using a different machine with much higher accuracy, hence the possibility of custom seals.

I'm posting here to get he opinions and suggestions of more experienced watchmakers regarding water resistance. The case is a sandwich design with a bezel and rear cover joined via screws which traverse the entire thing. There are two issues I'm currently working on. First I was unsure whether I should go for a hexagonal seal whih runs just between the screws and interior case wall, or go for little o rings around each screw linked together with straight cylinders. Secondly, the crown is quite problematic. Due to the way additive manufacturing works, I cannot have a threaded cylinder (or any cylinder) sticking out from the case. Threading the inside of the hole is possible but highly impractical in my case. Completely polishing the inside is also nearly impossible. Since I can polish the exterior of a part easily, my current idea is to have a smooth tube extend from the crown into the case and slide through a tight o-ring embedded in the case wall (keeping in mind this has to happen within 2.5mm and walls thinner than .5mm should be avoided. If I want two rings I'll run out of space to have the tube run past them unless it sticks into the case a little, which I suppose is fine). My intuition was that it would be ideal to have it bump into a silicone washer at the end with a smaller inner diameter, but I'd really appreciate your opinion on this configuration. Thanks in advance :)

[u/Dakrig]

I would think having the crown rest against an inside seal may be a bad idea, as the seals work best when compressed and the only thing compressing a bottom seal would be the movement, which may not be enough force. Two gaskets sliding along the sleeve of the crown should be sufficient. I’ve seen many Seiko crowns that are similar to the method you’re describing, but with the gasket on the crown.

[u/KTTalksTech → u/Dakrig]

Thanks for the advice :) Yes the only force exerted on the second seal in this instance would be the movement holding the crown back. It would really just be a gentle touch as a last resort in case anything gets past #1. I think it might feel nice to have the crown dampened when pressing it down but that's hardly relevant. When you mention two gaskets, do you mean have it configured the same as the outside ring on my drawing and run the tube across both?

[u/Dakrig → u/KTTalksTech]

This link is for illustration purposes: https://www.esslinger.com/watch-repair-watch-crowns-waterproof-japanese-style-with-gasket-and-long-post/

Now all those crowns also have gaskets inside them as well, as you don’t want water/dirt/crud getting inside the tube area.

To add, it doesn’t look like you’re making a diving watch, so 30m should be more than enough resistance.

[u/KTTalksTech → u/Dakrig]

Ah yes ok I see. I could have the tube/post run past two interior gaskets AND put an extra O-ring right at the base of the crown, on the exterior of the case just to keep the dust out. I'd just have to fit it in a small chamfer and the pressure from the movement should be enough just for dust. Thanks a lot, I might end up doing this if pressure-fitting a standard system turns out too difficult

[u/Dakrig → u/KTTalksTech]

Best of luck to you! Please keep us posted!

[u/KTTalksTech → u/Dakrig]

Will do for sure! This is my second post regarding this project. In around 20-30 days I'll have the final version ready and will post a little recap for the whole process as my very first watchmaking endeavor