Achieve mechanically water tight snap-in-place joint

Question

I'm not sure how to ask it but i'll try

I want to 3d-print 2 half spheres with a screw cap that then can be clipped once (can't un-clip later) And can be filled with water (lets say its food safe, i'll also coat the internal to waterproof it)

So, is there any known mechanical way to create a joint that will prevent water leakage?

it might be easier if you don't split the opening with the bottle cap. Then you could have a cone type seal with external snaps (maybe a bit clunky looking). The idea with conical seals is that the male angle is slightly different from the female angle, and there is a slight interference and flex resulting in a circular contact line. — Pete W, Jul 31 '21 at 02:03
finely polished steel surfaces will weld themselves together. — Tiger Guy, Jul 31 '21 at 04:46

score 1 · Answer 1 · answered Jul 31 '21 at 01:00

For a static joint, there are basically three options:

Use an adhesive of some sort to overcome irregularities in the mating surfaces.
Use a gasket to overcome irregularities in the mating surfaces.
Use sufficient clamping force to overcome irregularities in the mating surfaces.

For a purely 3D-printed object, option (3) is out: you can't get sufficient precision on the clamping and mating surfaces to prevent leaks. That leaves whichever of (1) or (2) is better for your application.

But if you're 3D printing, why print the object in pieces? One of the strengths of additive manufacturing is that you can make objects such as hollow spheres that can't be made in a single piece using subtractive techniques.

NMech · Answer 2 · 2021-07-31T11:29:55.043

My advice is to change the design if possible from vertical split to horizontal. i.e.

horizontal	vertical

Better	Not so good

The reason is that :

in the vertical solution the internal pressure will tend to separate the halves

figure 2: Forces developing on a half of cylinder due to internal pressure (source: Mathalino

you could go for a design that is hemicylindrical (lower part cylinder, top flat). In that version, you wouldn't need to worry so much about sealing if the vessel was static.

figure 4: variation with lower cylinder and top flat

Finally in general the dimensional accuracy of 3D printing does not lend itself for precision sealing. IMHO, it would be best to design perimetrical grooves around the sealing surface and then use an o-ring.

If you are feeling particularly adventure you could design the parts in such a way that they need to slightly deform when you put them together (i.e. they are pushing together). That will help the O-ring perform better.

score 0 · Answer 3 · answered Jul 31 '21 at 13:28

Do you need the rigidity of the part? The seal is always the problematic detail and if you are going to waterproof it you might as well use a separate membrane.

This reduces your problem into putting paintballs / laundry pods / liquid filled satches into a rigid ball.

Achieve mechanically water tight snap-in-place joint

3 Answers3