Need help

[Guest]

Hey guys. So i'm building a sub from scratch on my own. Its for the challenge and to keep me busy during covid. I have the electronics all done, and on a tray that fits my wtc.
But now i'm trying to make my WTC....WATER TIGHT! Here's where I am. I am using a ABS pipe. (yes I know acrylic clear is better but for my purposes this will have to do until I can justify the expense) Inside diameter is 76mm.
I could not find a O ring that was 76mm. But I do have one that is 3 inches. So about 76.2 mm.
I am 3d printing most of the parts I need. While this has worked very well for the hull and everything else. The end caps are giving me trouble. I cannot seem to a good fit/seal. I have done about 6 or 7 attempts with okay seals. But nothing 100% water tight. I am always getting a bit of leaking. I can print caps that fit with a very high degree of precision. I even tried some outside the box thinking. Got some gasket sheet. And cut a collar around the cap and fit it. Had some seeping.
So here's where I'm at. Even though I'm printing at 100% infill the print may be porous. I have a way of sealing it. Which I will try when I'm off work next. (12 hour shift nurse...losing my mind right now).
I've also found that the o ring has a bit of play to it. I printed a cap that fits perfectly the 76mm. I was thinking rather than inside the tube to place it between end cap lip and lip of the cylinder and use the pressure of the threaded rods to stop water from entering. For this I'll work on the edges of the cylinder and make sure they are true and as smooth as possible.
I'm sure this is as clear as mud. But I'm at work and just trying to fire this off between tasks.
Any help/advice would be appreciated.
What steps am I missing? What am i doing wrong?

[Ralph --- SSBN 598]

You have sealed your 3D printed end caps. (I hope this is true)

I have several submarines. I have one I use for testing new ideas in.
It has gone through 7 modification where everything in the cylinder has been changed.
The rear cap would not stay in place.
The last modification uses a piston, a lot of pressure is built up in the cylinder and the rear cap would pop out of the cylinder.
I also needed a little longer cylinder by about 1/32".
I did not buy another cylinder.

I fixed both issues by adding a second o-ring.
The original o-ring is in the groove.
The second o-ring is on the cap ledge between the cap rim and the cylinder edge.
Because of the cap popping out from pressure, I added 2 long brass tubes with threaded bolts in the ends and then added 2 aluminum 1/8" thick flat bat across each cap to tighten down so the pressure could not pop the end caps out.
Here is the front and read end caps.


Here is the rear end cap with the inside o-ring removed for easier access while working on the electronics.


I do not have to tighten the safety rods more than just keeping then hand tight.
I do not compress the outside o-ring.

I have tried this without the inside o-ring and have no leaks.
But I use the inside o-ring because it keeps every thing lined up and does not let any thing move.

One more thing, I clean and apply silicone grease to the cap o-rings when assembling the cylinder just before running the boat.

[cheapsub]

The in side of the ABS pipe is not machined round. Try a thicker O ring.
Try this to make a O ring.

https://youtu.be/o8LU-abFFe8

https://youtu.be/aweDWuNkPw0

Or look for O ring making kit.

[X Bubblehead]

There are a lot of undefined variables, such as smoothness of your 3D print, depth and width of the O-ring channel, tolerance of the cap OD to the ID of the pipe.

If you're using a cheap printer, (<$1000) that could be part of the problem, but without more accurate dimensional data from you, there's no way to know.

Proper O-ring applications are based on engineering principles - the DIY method of throwing O-rings at something until it works wastes time or could bottom your boat. Do it right, or do it over. It's always cheaper to do it right the first time.

What are you using to lubricate them?

Have you read the Parker O-Ring Guide? If not, start here and heavy-up: https://parker-store.by/pdf/cat5/ode5712.pdf

I've used O-ring and gasko seals that hold to hundreds of feet. More info here: https://www.parker.com/literature/Se...CSS%205124.pdf