Robinson Coupling

The Robinson coupling is a simple way of joining two bottles together using some threaded rod. The idea is first believed to have been used by a guy called Bill Robinson, hence the name of the coupling. See this page for more information on this.

I was having quite a bit of difficulty finding threaded rod/nipple in UK. I finally found a source, Ryness. They sell all sorts of lighting equipment and the threaded nipple’s that we need are used in lamps. They sell two sizes, 7mm and 9mm. Although the 7mm is smaller, I have found that it is easier to create the joint with them for a number of reasons. Firstly trying to drill the bigger hole, though only by 2mm, puts a lot more strain on the bottle. I found it quite hard to grip the bottle without it buckling whilst drilling a 9mm hole. Secondly the washers used to protect the inner tube which create a seal, don’t fit into the bottle cap without having the edges filed down. Lastly the socket set bit doesn’t fit in the bottle/cap so you have to use pliers which means its a lot harder to tighten.

By all means if you want to use 9mm joints for the extra flow, go for it, but they are a lot harder to construct.

Here’s a step by step on how to create a robinson coupling.

Materials Required

  • Some old inner tube or piece of thin rubber
  • Thread nipple
  • 2xNuts
  • 2xWashers
  • 2xbottles
  • 1xbottle cap

Tools Required

  • Socket Set
  • Drill with various drill bits up to 7mm
  • Soldering iron (not essential)
  • Knife/file
  • “Pusher Rod” – just a bit of pvc pipe with internal diameter of 7mm to push the coupling through the bottle

1. Use a soldering iron to melt a small dimple in the centre of the bottom of the bottle. This makes sure that the drill will not slide off as you start drilling.

2. Work your way up to a 7mm drill bit and then use a knife to clean the hole.

3. Repeat the above for the bottle cap.

4. Assemble half the coupling as follows nut->washer->inner tube and insert into the bottle.

5. Using the “pushing rod” push the coupling through the hole and then place some more inner tube on the exposed nipple.

6. Now place on the nipple in the following order bottle cap->inner tube->washer->nut.

7. Tighten as much as possible without the bottle buckling.

8. Screw the top bottle into the bottle cap.

Here is a picture of what your joint should now look like

And looking inside the bottle

And below is a diagram detailing the components and how they fit together

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