How to make a rotary switch o-ring seal?

[QuadCoreInside]

Hi all,

We're working on a diy plexiglass underwater case for my camcorder. We've completely sorted out the shape and dimensions of the housing itself, but there's still one challenge to be dealt with.

We want to control the camera's start/stop button by a rotary switch in the right side panel of the housing (which is also the lid).
At the moment, we have made a design as seen below (back view). The axle is to be a smooth 6mm rod, with metric thread cut on both sides to allow the nuts to be screwed on.

The switch will be rotated counterclockwise, so the tip of the switch will move forward and press the start/stop button.

We wonder if this design will be waterproof at 30 metres depth. What do you guys think? Any improvements maybe?

 

[tbone1004]

you need an Ikelite control gland and control shaft. If done right it will be tight until much deeper than 30m

 

[miketsp]

I don't much like the idea of the threads. I'd do what most commercial housings do, use a smooth rod with a groove cut in to accept a circlip to keep the rod in place.

 

[QuadCoreInside]

Ikelite control glands are not suitable for us, because of the non-metric dimensions. We just want to know if this is going to work, or how we should tweak this design to make it work.

 

[diversteve]

It's hard to tell from your drawing but I think your design will leak around the shaft where it goes into the axle since all your o-ring does is seal the axle against the inside of the case. Since the pressure will be from the outside trying to get in, that's not the best design for that either.

Optimally groove the shaft on both sides inside the axle housing and press it in with two o-rings but that may be hard to turn if the fit is correct. Also add an o-ring under each nut. I'm not even sure if this would work franklly.

I do have a little experience with rebuilding the front port on a poly housing - it used an o-ring outside and an o-ring inside. The inside of the port was grooved to accept an o-ring but it still leaked between the threads. Where it was leaking was along the face of the housing into the threaded port.

Adding a 2nd o-ring to the outside captured by a threaded ring solved that problem - that would be a similar idea to the outside of your design.

For reference, here's what Ikelite does. Their exploded views might help:

Ikelite | Camera Control Levers with Knobs
Ikelite | Camera Control Glands for 1/4-inch Shafts

You can buy a non-metric tap for your housing and cut a standard thread into your plex and use Ikelite's instead. They're only a few bucks...It's probably never going to come out and it's just a one-off for your use right?

 

[tbone1004]

it should work since that is basically how the Ikelite works. Build it and put it in a pressure pot and see

 

[QuadCoreInside]

Miketsp, the thread will only be at both ends, in the middle (where the o-ring will be), the rod will be smooth. No problem for the waterproofness of the o-ring seal.

I don't much like the idea of the threads. I'd do what most commercial housings do, use a smooth rod with a groove cut in to accept a circlip to keep the rod in place.

 

[miketsp]

Miketsp, the thread will only be at both ends, in the middle (where the o-ring will be), the rod will be smooth. No problem for the waterproofness of the o-ring seal.

I understood that from the drawing but it seems that as you rotate the rod it will drive in and out due to the thread and will not be pure rotation on the o-ring. May tend to unseat the o-ring. Plus in practice the run-out of the outside thread will be very close to the o-ring. Threads only end abruptly on drawings, not in real life. My opinion is that construction with circlip(s) will be much easier and safer in practice.

 

[QuadCoreInside]

I understood that from the drawing but it seems that as you rotate the rod it will drive in and out due to the thread and will not be pure rotation on the o-ring. May tend to unseat the o-ring. Plus in practice the run-out of the outside thread will be very close to the o-ring. Threads only end abruptly on drawings, not in real life. My opinion is that construction with circlip(s) will be much easier and safer in practice.

Good point! My idea was to not thighten the nuts to the housing, but to carefully cut the threads so that the nuts will jam at the right distance. Then there will be a little room between the nuts/washers and the plexiglass. The rod will rotate freely together with the nuts, so will not drive in or out.
About the small distance between the end of the thread and the o-ring: this is only applicable on the inside, I could add one or two washers between the nut and the initial washer to increase the distance. Won't be a problem. I also could fix the big washer to the inside of the housing, to prevent the o-ring from popping out.

To be honest, I more or less copied this design from youtube, this clip to be precise. This is a pushbutton, but the o-ring design is the same. This guy also fixed the inner washer to the housing.
[video=youtube_share;6ncAdZzdTqw]http://youtu.be/6ncAdZzdTqw[/video]

 

[Bob DBF]

Hi all,

We're working on a diy plexiglass underwater case for my camcorder. We've completely sorted out the shape and dimensions of the housing itself, but there's still one challenge to be dealt with.

We want to control the camera's start/stop button by a rotary switch in the right side panel of the housing (which is also the lid).
At the moment, we have made a design as seen below (back view). The axle is to be a smooth 6mm rod, with metric thread cut on both sides to allow the nuts to be screwed on.

The switch will be rotated counterclockwise, so the tip of the switch will move forward and press the start/stop button.

We wonder if this design will be waterproof at 30 metres depth. What do you guys think? Any improvements maybe?

I would have another o-ring on the outside of the housing under that washer as well.

I also agree with miketsp "I don't much like the idea of the threads. I'd do what most commercial housings do, use a smooth rod with a groove cut in to accept a circlip to keep the rod in place." The problem with threads is that they have to be kept away from the o-ring, and those washers give you little tolerance for error. Ending the threads too soon won't tighten the gland enough and ending them too long they may snag the o-ring.

Good Luck

bob