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  • O-ring seal?

    I am making an underwater housing (needs to be good to 150 feet) with O-ring seals. I am new to 3D printing, and will be handing stl files to a friend to do the actual fab. What I do not know is how well O-rings seal against 3D printed materials. In this case the seal will be between a groove in a printed part and the inside of a length of SCH 80 PVC pipe. Any insight/guidance would be appreciated!

    (And a quick question that is probably in a FAQ somewhere. Given the name DrVAX, is it safe to assume the proprietor was a VMS guy back in the day?)

  • #2
    A 3D printed underwater housing good to 150 ft.??? I'm not sure how doable this really is. It seems like you're asking a lot. For sure it would have to be really thick.

    Guys, what do you think; is this a crazy idea?

    And, yes, Irv worked for DEC back in the day.

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    • #3
      Originally posted by Ender5r View Post
      A 3D printed underwater housing good to 150 ft.??? I'm not sure how doable this really is. It seems like you're asking a lot. For sure it would have to be really thick.

      Guys, what do you think; is this a crazy idea?

      And, yes, Irv worked for DEC back in the day.
      I am bad at physics, but this sounds like a huge amount of pressure and the seal seems to be the least of the problems here.

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      • #4
        I go back with DEC to PDP 11/45s. Back in the day part of my job was going around the country shoving nonstandard Q-bus boards into microVAXen, stuffing them with 300 MB Maxtor drives (for only $4000 a pop - amazing!), and connecting them to things like 9-track tape drives. This actually annoyed DEC at the time, because their usage model was having microVAXes surrounding a 780 which drove peripherals. They looked at us askance when we decided that for our uses we didn't need the 780s at all. I even wrote a bunch of real-time instrument control software. Turns out you could do a lot with all of those sys$you_name_it calls! None of which is relevant to the question at hand...

        I am a physicist ;-) and the overall specs are easy. 150 feet is only about 5.7 atmospheres, or something on the high side of 80 psi. That's not that much higher than in-home water pressure, which is typically about 50 psi, 1-1/4" Schedule 80 PVC is rated to 520 psi, which means it probably would hold 1000 psi no problem. The issue is having a water-tight seal on an end that can be opened and closed. That's easy to do in principle. I don't trust just using a threaded cap to protect electronics from leakage, but you can use a threaded cap to press a plug with O-rings into the pipe. The plug is what I would like to print.

        That's the bit that I don't know anything about. My partner-in-crime's printer is a Prusa that prints with PLA. I have no clue how well an O-ring in a printed grove will seal. I could machine it, but it would be a lot more fun to print. If it works I can imagine all sorts of fun uses!

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        • #5
          OK, if I read you correctly, you are planning to have electronics inside a PVC pipe whose end is sealed with a 3D printed cap. Is that about it? To me, the main issue would be to make the O-ring big enough, so that it can have enough squishiness to make a really good seal.

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          • #6
            That's basically it. If this were machined aluminum on machined aluminum it's easy. But you raise the right question. What O-ring polymer and size is the best match for the surface texture and tolerances that can be achieved with a printed part? This is my first foray into this kind of fabrication, and I'm finding myself chasing a variety of interesting technical questions. But the more I think about it, the more I see a 3D printer in my future, especially if things like pressure seals are an option.

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            • #7
              Obviously, a testing plan is a requirement. Caps of different sizes, rings of different materials & sizes, some weight inside the pipe so it will sink, possible wrapped in paper towel or such like so it's easy to see if any water got in. Unless, of course, you just happen to have a pressure chamber available

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              • #8
                Absolutely on the testing plan! I've bought that particular T-shirt a few too many times. No, no handy pressure chamber. 😆 Weight it down, lower it to depth, and let it stay there for a while.

                I've also been looking at smoothing options for PLA such as dichloromethane steam, or the Polymaker brand of PLA that can be smoothed with isopropyl alcohol. I'm thinking a place to start might be careful sanding, followed by smoothing. Any experience with that part of the process?

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                • #9
                  PLA cannot really be smoothed. There are brands claiming that, but in the end they just add solvable components. Removing components is more or less uncontrolled removing of structural parts. Or they claim it is still PLA because of the print behavior, but practically it is something completely different and you have no idea what chemical shit evaporates.

                  ABS is the way to go there. Acetone and a few minutes of bathing the part inside the fumes to get a shiny part.

                  If I would go for a smooth part, I would go for resin printers. It provides proper resolutions, but is messy.

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                  • #10
                    jhester, Geit (as usual) makes a good point. And it has implications for the printer you buy. Your best bet for ABS is an enclosed printer that you can vent either through an activated carbon filter or to the outside. Perhaps a Monoprice Ultimaker II would be a decent option: reasonable price & build size, & it's enclosed. Plus DrVAX thinks quite highly of them.

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                    • #11
                      Thanks for all of the great feedback! It has led me to a lot of interesting digging. I have an approach in mind. It will be awhile before I know anything but I’ll post when I do.

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