Robinson Coupling

I finally got the pieces together this weekend to do my first Robinson coupling. I used pretty much the parts as Bill Robinson (the guy who came up this method) suggests. Parts are

  • 1 x piece Threaded Lamp rod approx 2.5cm
  • 2 x nuts for the rod
  • 3 x rubber – washers made form bike inner tube
  • 1 x bottle cap
  • 1 x 1.25L P&L empty bottle

Also the tools needed were

  • 1 x 10mm drill bit
  • 2 x 14mm sockets
  • 3 x socket extenders
  • 2 x socket wrench
  • 1 x metal coat hanger
  • 1 x glue
  • 1 x sharp scissors
  • 1 x sharp blade

Once you have everything together its quite simple. The hardest part was getting the threaded lamp rod. I visited a lighting shop and was going through the lamps etc. When I asked the shop owner he came out with a jar full of 2.5cm length lamp rod sections and a jar of nuts to fit. The nuts I found in the hardware stores were all too big to fit in the bottle cap so finding all of these pieces together was great. Better still the guy gave them to me .. no charge :) I will have to go back and get some more, it might cost me a few $ but not much.

First step was to drill the 1.25L bottle. I drilled a 2mm hole through the very centre, the thickest part of the bottle. I then used successive drill bits, stepping up 2mm at a time until I got to the 10mm bit. I used this method so I didn’t gouge out a bit of plastic and to keep the hole edges very precise. I also used the sharp blade to clean up the edges.

1.25L Bottle - 10mm hole

1.25L Bottle - 10mm hole

Next step was to drill a hole in the bottle cap. I used the same method. I don’t have a vice (I should get one) so I held the cap with a pair of wide jaw pliers so if the drill slipped it didn’t get my finger.

I then prepared the washers. I used a bike inner tube, cut a section and opened it flat, drew a circle using the outside of the bottle cap, then cut just inside the line I drew. I did this for 3 washers. I then cut out the inner circles. For the one that will fit in the cap of the second bottle, I cut out the hole just bigger than the hole in the cap. For the other two I did it just smaller, so it would be a tight fit around the lamp rod.

"Robinson Coupling" parts

"Robinson Coupling" parts

You can see the washer top right is slightly smaller in diameter. I found that when I tried to push it in the bottle opening of the bottle with the 10mm hole cut in it, it wouldn’t fit through. So I trimmed it to fit. As long as its bigger than the nut, it will be ok (The nuts are 14mm BTW)

I used a drop of superglue (should use thread lock but I don’t have any) and glued one nut to the end, then added the (smaller diameter) washer. I then came across a interesting problem, how to insert it into the bottle and get it through the hole so I could attach the other end. The solution ended up being simple. I used a metal coat hanger and slipped it through the bottle hole and up through the bottle opening, I then just slid the lamp rod and nut down and into place.

Metal coat hanger to the rescue

Metal coat hanger to the rescue

Lucky I have a few socket sets around, some of them minus a few sockets, but they all had the socket extender bars, so I just clipped three together and put the 14mm socket on the end and inserted it into the bottle to hold the nut.

socket extenders

socket extenders

You can see here how the socket extenders and the 14mm socket, hold the piece of threaded lamp rod and nut in place.

Lamp Rod held in place

Lamp Rod held in place

Next on goes another washer, you can see the washer is tight around the lamp rod.

Middle Washer in place

Middle Washer in place

Then on goes the bottle cap, the last washer and the final nut. These are then tightened down with a socket wrench with another 14mm socket on it. I just held the other socket extension bar in place with another socket wrench while I tightened the top one down.

bottle cap washer and nut in place

bottle cap washer and nut in place

Only thing I noticed is that the rubber washer in the bottle cap will tend to deform a little as the top nut is tightened down. I will probably need to make this slightly bigger for future Robinson couplings as the first leak test I did, it was leaking a little in one spot in the cap where the washer folded up a little and didn’t seal properly. I pushed it down in place, fitted on another bottle and it held pressure fine.

2 Bottles in robinson Coupling attachment

2 Bottles in Robinson Coupling attachment

I haven’t done a 100psi pressure test yet, only about 20psi one. Reason being it was late and I didn’t want to wake the neighbours with an unexpected bang :) But I am happy with the connection. Big thanks goes out to Bill Robinson for the idea.

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This entry was posted on Monday, August 25th, 2008 at 12:37 am and is filed under Development. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

 
 

6 Responses to “Robinson Coupling”

  1. Socket Wrench Says:

    Applying pressure to all six flat sides of a nut or bolt with equal force reduces the stress … Socket Wrench

  2. Mitch Says:

    Good ole’ Robinson! I need a cap to cap fitting and was going to try the glue into a sheath method. I am thinking I may still use a robinson fitting, to ensure it does not separate though.

  3. todd Says:

    try the tornado coupling from georges website, this might be what you are after.

    http://home.people.net.au/~aircommand/index.htm

  4. Josh Says:

    Hi

    I live in Hornsby and was wondering what lighting shop you went to for the lamp rod I’ve been everywhere…..

    Josh

  5. todd Says:

    Josh,

    I went into a small lighting shop in Rockdale near where I work and the guy had a whole glass jar full of them and just gave me a few. Make sure you get bolts that go with them, they all come together.

    There is a lighting place in Salisbury Road Asquith that would probably have some. Tell them what you are using it for and they will probably give you a few for free, if not they shouldn’t cost much a few dollars at most.

  6. josh Says:

    thanks alot