Methods for making Robinson Coupling

[air.command]

Ahh that makes it a bit clearer. What size hole do you have there in the bottle? We found that beyond around 14mm we just could not get a good seal even with flat washers. It's because of how the base of the bottle is shaped for the penta-claw. How do you seal between the cap and the bottle that screws into the cap?

[Brian]

That test was only 1 o-ring between the bottle and lid so this time I might try washers instead. The hole drilled into the bottle is 16mm, so I might try melting that area flat.
I never thought of why the bottom was that particular shape.

[Blenderite]

How do you tighten the nuts on the metal couplet?

[Nick B]

I'm going to just use a buttload of hot melt.

I have two 4 liter rockets with lamp rod couplers joining them in the butt.

One has multiple rubber seals with internal gorilla glue and one has hot melt external only.

both use washers with the nuts.



The one with the seals keeps leaking after impacts or several normal launches, and the adhesives keep fracturing.

The one with the hot melt has not yet failed.

Roughly the same has happened with DIY tornado couplers with lamp rod n seals/o rings.

I'm now using hot melt and t8 flt to create homemade tornado couplers instead of the lamp rod.
So far they are holding up really good.


It's just a pain in the butt and expensive to use the rod, o rings, seals, time to chop up the lamp rod and deburr, and repeated adhesives unless necessary.

I'm hoping to move on to larger fittings since I dunno how these people with full bore 4 plus liters are using couplers with small IDs to maintain flow and thrust to a full bore pet bottle opening.

[Brian]

Hot melt glue is suprisingly effective but the issue is that it is weak when hot and brittle when cold.
An easy and simple coupler made by BWR that I use because it's light and can have a large ID http://bwrockets.blogspot.com.au/2011/0 ... cones.html
The biggest ID they've survived in my tests is 20mm
Construction video

This method should be posted in the 'How To' section

[Nick B]

Hot melt glue is suprisingly effective but the issue is that it is weak when hot and brittle when cold.
An easy and simple coupler made by BWR that I use because it's light and can have a large ID http://bwrockets.blogspot.com.au/2011/0 ... cones.html
The biggest ID they've survived in my tests is 20mm
Construction video

This method should be posted in the 'How To' section

That's hawt.

I'll hafta give that a shot.

I just picked up some 1/2" sprinkler nipples n 1/2" conduit nuts today.
I'm gonna tear down the 4 liter with lamp rod n washers and redo it with the larger nipple, throw on a tornado to make it 6 liters, pressure test, n let it rip.

This is going to get alot more enjoyable than splicing bottles and waiting three days to pressure test and move forward.

[U.S. Water Rockets1]

Hot melt glue is suprisingly effective but the issue is that it is weak when hot and brittle when cold.
An easy and simple coupler made by BWR that I use because it's light and can have a large ID http://bwrockets.blogspot.com.au/2011/0 ... cones.html
The biggest ID they've survived in my tests is 20mm
Construction video

This method should be posted in the 'How To' section

We have not had very good luck with hot melt glue. It tends to peel off to easily, even when not exposed to any severe treatment. There are some new silicone glues on the market which harden in 20 minutes that we have tested and they seem to work better and stay flexible under cold conditions too.

[Nick B]

Yeah.

It does have plenty of limitations. I'm not getting into pressures above 120 psi yet, And I doubt it will hold much pressure past that for the couplers, but we are only using it for around the couplers for sealing, and tornado fittings and wings. That extent seems to be working out good for us. We are prepping a ftc for hot melt only application to see how it will work out with higher pressures at mid summer temps. But for the most part, it's still PL for most our work.











But i'm gonna take that gorilla glue and use it for outdoor rifle target practice.

[Maru Ivan]

Cool. That's the technique (gluing the coupling together) I'm trying right now. I may use o-rings/rubber washers on the cap and on the inside of the bottle (and also might use a third one in the middle) to completely seal the whole thing. I'm going to use the o-rings found on 9mm Gardena nozzles to pre-stretch the seals. Hope this works.

[bugwubber]

Here's my take-

It does not leak and only uses pvc cement .
The trick is to use a pipe clamp to squeeze the fittings together while the pvc cement sets.

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[flett044]

Can you tell me how to make your coupling ?

[flett044]

Above post for bugwubber

[bugwubber]

Sure I haven't finished writing up the instructions yet but here's the materials list:

1 bottle
1 bottle cap- preferably a more substantial one.
2' section of 1/2" CPVC
2' section of 1/2" PVC
2 3/4" soft rubber washers
PVC cement
1 bottle nozzle cut off above the ring handle
24" pipe clamp or similar.

You will cut off a 1/4"- 3/8" section from the 1/2" PVC
Coat the inside in PVC cement Slip it on to the the end of the 1/2" CPVC pipe.

While that cures,
mark center on the pentaclaw end of your bottle and drill a 5/8" hole (match the outside diameter of the 1/2" cpvc
Cut off a 1/2" section from the PVC, assemble bottle cap, cut off bottle nozzle and 1/2" pvc.
Using the bottle nozzle and pvc piece as a guide, drill 5/8" hole through your bottle cap.

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Set aside.

Take your CPVC with the PVC ring on,and slide 1 washer on.
(you may need to trim this washer down during this step)
Insert the CPVC into the nozzle of the bottle through the bottle,and out the hole you drilled.

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Install the second 3/4" washer, flush against the bottle.
Install the bottle cap flush against the washer.

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Check alignment, last chance to replace bottle if crooked, off center etc.
Cut CPVC flush with bottle cap

Cut one 2" section of PVC and another that is a couple inches longer than your bottle.

Insert the long piece of PVC you just cut into your bottle through the nozzle, up to your coupling.

Have pipe clamp ready...

Put cement in one end of the 2" pvc piece
Put the cemented end on the CPVC that is sticking out through the bottle cap

Apply pipe clamp and quickly squeeze the assembly together until the rubber washers are compressed.

Let cure.

Remove clamp and long pvc pipe from bottle.
Cut 2" pvc piece flush with bottle cap. And clean up the edges.

You are done and ready to launch!
OR
Make more!

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[bugwubber]

There is an alternate to the washers- you can use PL Premium.

To do this, you must sand around the hole you drilled in the bottle both on the outside and inside.
The cap must also be sanded and roughed up.
Put PLP on the CPVC and PVC ring before inserting the CPVC pipe into the bottle.
Use a liberal amount of PLP on the outside to give the cap plenty of support.

If the coupling develops a leak at the field, you can add a little fix-a-flat as a temporary patch.

[flett044]

Thanks so much, I got a weekend project now