Underwater Housing for miniDV

Step 3 Overall Assembly

Since this is quite customized per camera, I can only give you general guidelines.

One end of the assembly gets an acrylic window glued in. This is the sealed or non-removable end (left in the diagram). This end requires a 1/2" thick acrylic disc cut into a nice circle. I put the 4" pipe on top of the acrylic and traced the circle twice, rough cut with a jig saw, then mounted it to the PVC pipe using double sided tape and used a pattern maker bit on my router table to make a perfect disc. I'm sure it doesn't have to be this perfect, but you'll use more epoxy if it fits into the coupling loosely. You might as well cut both discs at the same time.

Hint: leave the protective paper on the acrylic for as long as possible.

Make two of the following:
Insert the disc into the coupling until it hits the stop. Use a pencil to trace on the paper against the stop so you know how much paper backing to remove when you glue it in. I just used an exacto to cut that small ring of paper off. Run a thin bead of epoxy in the stop and also on the side of the coupling where the disc will sit. Push the disc in and put some weight on it. A can of soup works. Let it set up for 10 minutes, or overnight.

Keep in mind, I trimmed the length of my couplings but it's not exactly easy to make nice square cuts. If you think you want to trim them, Do it BEFORE you glue in the discs. NOTE, the faces where the Oring sits must be smooth so I used the factory edges of the coupling. Of course, if you have a milling machine, you can go nuts with this. My purpose was doing as much as possible with readily available garage tools.

One final tip on the gluing process. Use masking tape on all adjacent areas because the glue goes everywhere. It's much easier to peel the tape before the epoxy or cement starts setting.

Comments

[ermaclob]

as im making mine i start to notice that it is kinda hard to take the coupling of the pipe once it goes all the way in. how do you easily remove the end coupling once its all done?

[Bobby_M]

If you look at the drawing, the coupling that becomes the removable cap only overlaps the pipe about 1/4" before the oring stops it. On mine, it provided no resistance to removal.

[ermaclob]

im using 6" pvc, 1/4 into the coupling is very loose . thats making me worry. i want ~ 1 1/4" in the coupling. any recommendations on longer latches?

[paratroopaah]

On my design, if I install the end cap without the o-ring in place, the o-ring can be pushed into the gap with just a small amount of force. Should I shave off some of the 4" pipe to get a more snug fit?

Steve

[Bobby_M]

Yes, absolutely. You want that gap to be too tight to even push the ORING in because when you start taking on pressure, you want the cap to be able to compress the oring as much as it wants to. You don't want the cap to bottom out on pipe. I'd say take 1/8" off. Just my opinion.

[peterthehun]

Instead of a back view port, I just used a PVC end-cap - one less potential leaker.

[Bobby_M]

I understand the benefit to a cap on one end but I like to be able to see inside from my viewpoint in case there is a leak. I can also see through the viewfinder to look at battery life, etc so that I know when to stop framing shots when the tape runs out or the battery dies. My version two housing doesn't use a glue joint in the back but still allows seeing in.

[Rich_D]

If you wanted to use a screw-on end cap, couldn't a hole be cut in it for an acrylic window to be added? I guess then the question would be which seal do you trust more: the one on the permanently-affixed housing, or the one on the screw cap? I think it would be easier to bore a round cut in the screw-cap than to cut an exact line in the pipe; What do you think? (Also, does Home Depot actually have clear PVC end-caps?)

[peterthehun]

usually with pipe threads (tapered) you have to seal them with teflon tape. that's good for houses but i wouldn't use on a case like this. you could otherwise use a paste/glue to seal it but there's no guarantee... the "appropriate" way is to use teflon tape I believe... i dunno, maybe an o-ring would do the trick?

[Bobby_M]

I've played around with the threaded fittings a bit but there are some drawbacks. For one thing, they're huge and add a lot of bulk. Cutting a nice hole in the rounded cap would be pretty difficult. Home Depot doesn't sell clear PVC, but it is available an really expensive.

[1234]

If you find a acrylic cap that matches nice with the pipe could this be used instead of your design also would pressure affect this to come off & on upto 40 meters in depth.

[Bobby_M]

An acrylic cap would be great, or even a "mostly" clear PVC version but these fittings are cost prohibitive. Probably $30 or more.

[paulthenurse]

The other thing I'm considerign doing is doubling up the walls. I bought a couple of slip couplings, teh kind that you can slide the leanth of the pipe because it doesn't have the internal stop. My plan is to glue 2 couplings to a leanth of pipe. The end of one of the couplings will be the o-ring seat. The other end will get a regular hub fitting that I will glue in place and use the internal hub stop to act as the other lens seat. If this works as I hope, I'll have 2 layers of pvc without having to do any heat forming. Thoughts?

[Bobby_M]

The idea of full double wall did cross my mind in both my designs and the one pressing benefit is that fortifies the two open joints I have in the center of my housing body. That is, if both of my coupling ends touched each other in the middle, it provides for more surface area for gluing. The other benefit might seem to be more resistance to implosion, but single wall schedule 40 should already resist hundreds of feet of depth so going thicker is of no added benefit that I can see.

[paulthenurse]

Bob, is there a reason why you wouldn't add a second O-ring at the top of the body, where it sits against the inside lens seat? It seems to me that if you do that you would get a double seal. The only dificulty I see is that the o-ring is not held in place by going around something, but rather held in place inside the ring. Maybe you would neeed to router a shallow groove just below the lens seat for the o-ring to sit in. Paul

[Bobby_M]

Hey Paul, I didn't catch your comments here but I did reply on this issue at Scubaboard. I actually think double end seals make a lesser "seal" because the hardness is actually doubled. In theory, if one design uses a "70" hardness O-ring, a double system should use two O-rings with a "35ish" hardness. Otherwise, the sealing pressure is not going to increase at the same rate as the water trying to get in. The only kind of double seal I'd promote with this design is one that is inset around the body of the housing. When the cap goes on, it slips past the captured o-ring and compresses it. In other words, it won't compete with the main O-ring.