Methods for making Robinson Coupling

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avfuelerict
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Methods for making Robinson Coupling

Post by avfuelerict »

Good day all.

I was interested in attempting a robinson coupling since splicing has gone nowhere. There is one issue with my trying to do this though.....I do not have access to a lathe. Does anyone know of any other methods that can be used to hollow out the threaded rod, or where to purchase hollow threaded rod?

Thanks
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Re: Methods for making Robinson Coupling

Post by WRA2 »

avfuelerict wrote:Good day all.

I was interested in attempting a robinson coupling since splicing has gone nowhere. There is one issue with my trying to do this though.....I do not have access to a lathe. Does anyone know of any other methods that can be used to hollow out the threaded rod, or where to purchase hollow threaded rod?

Thanks
Try these:

http://www.antiquelampsupply.com/category/175/

http://www.allproducts.com/manufacture1 ... duct4.html

http://compare.ebay.com/like/1904025277 ... 602_304662

The term to search for is "threaded lamp rod" and you might also check your local hardware store in the lighting section.
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avfuelerict
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Re: Methods for making Robinson Coupling

Post by avfuelerict »

After looking into it a little more, I found I was looking up the wrong thing BO: DOH: . I was looking for threaded lamp rod, which does indeed exist in the US, but it is a solid rod. I called up a lighting store, and they corrected me on what it is called. It goes by threaded nipple, threaded lamp nipple, and lamp nipple. I swung by and the guy said the cost would be a video sent to him :cl: WO: .

I am going with the larger 1/4 rod, but it is taking considerably more work than the smaller 1/8. I am having to grind out some smaller diameter metal washers to fit the larger rod. I also made a tool using the 1/2 inch pvc pipe. I just heated the end of the pvc pipe with a torch, and then pushed the threaded rod, with a nut on it, into the pvc. The pvc grew in outer diameter and would no longer fit into the bottle, so I gound it down a bit so it fits through the neck once again.

I hope this is of help to someone. I felt like an idiot for a while.
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Re: Methods for making Robinson Coupling

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avfuelerict wrote:After looking into it a little more, I found I was looking up the wrong thing BO: DOH: . I was looking for threaded lamp rod, which does indeed exist in the US, but it is a solid rod. I called up a lighting store, and they corrected me on what it is called. It goes by threaded nipple, threaded lamp nipple, and lamp nipple. I swung by and the guy said the cost would be a video sent to him :cl: WO: .

I am going with the larger 1/4 rod, but it is taking considerably more work than the smaller 1/8. I am having to grind out some smaller diameter metal washers to fit the larger rod. I also made a tool using the 1/2 inch pvc pipe. I just heated the end of the pvc pipe with a torch, and then pushed the threaded rod, with a nut on it, into the pvc. The pvc grew in outer diameter and would no longer fit into the bottle, so I gound it down a bit so it fits through the neck once again.

I hope this is of help to someone. I felt like an idiot for a while.
You didn't mention if you used washers. You should use 3 washers for the most effective seal (one under each "nut" on the inside of the bottles and one in between. PH:
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Re: Methods for making Robinson Coupling

Post by avfuelerict »

I will be using 3 rubber washers. I plan on assembling it today.

How long does the lamp rod need to be? I was thinking of making it jus barely longer (1/4") than what is needed to put it all together. It'd save weight.
avfuelerict
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Re: Methods for making Robinson Coupling

Post by avfuelerict »

I got the coupling put together. I pressure tested to 25 PSI and not leaks. I then pressure tested to 60 PSI and no leaks. I beleive I finally have a coupled rocket WO:

Now all I need to do is cut off the excess threaded lamp nipple to reduce weight and for more water to flow back into the nozzle end bottle when place on launcher.

Any comments, opinions, or advice as to the handywork?
Attachments
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robinson coupling with bottle in background.jpg
robinson coupling with bottle in background.jpg (92.42 KiB) Viewed 172 times
robinson coupling.jpg
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Re: Methods for making Robinson Coupling

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avfuelerict wrote:I will be using 3 rubber washers. I plan on assembling it today.

How long does the lamp rod need to be? I was thinking of making it jus barely longer (1/4") than what is needed to put it all together. It'd save weight.
Just long enough to thread the nuts on (you will probably wind up with a little extra once you compress the washers a little).
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Re: Methods for making Robinson Coupling

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avfuelerict wrote:I will be using 3 rubber washers. I plan on assembling it today.

How long does the lamp rod need to be? I was thinking of making it jus barely longer (1/4") than what is needed to put it all together. It'd save weight.
The only rubber washer that is sealing the coupling is the middle one. The other two don't seal as air will escape past them through the thread. So technically you don't need them, though it's still a good idea to use them to protect the bottle from the sharp edges of the metal washers.

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Re: Methods for making Robinson Coupling

Post by Drake Stutesman »

Being the 15 year old i am i had made a three bottled rocket like this one and got about 300 feet of air. my next project i made a 6 bottle 12 liter one of these and all the rocket had done was shoot up about six feet and hover there for 3 seconds??? im thinking i should try a different coupling any ideas?
If it doesnt work the first time it probably wont work the second, but most definitly work the third.
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Re: Methods for making Robinson Coupling

Post by U.S. Water Rockets1 »

WRA2 wrote:
avfuelerict wrote:I will be using 3 rubber washers. I plan on assembling it today.

How long does the lamp rod need to be? I was thinking of making it jus barely longer (1/4") than what is needed to put it all together. It'd save weight.
Just long enough to thread the nuts on (you will probably wind up with a little extra once you compress the washers a little).
It is also a good idea to use as large of a metal washer as you can fit inside. The larger surface area will spread the stress forces of launch over a wider area and reduce the chance of a crack or break.
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avfuelerict
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Re: Methods for making Robinson Coupling

Post by avfuelerict »

That's why I went with the washers for the 1/8 i.d. lamp nipple (threaded lamp rod) and enlarged the hole for it to fit on the 1/4 i.d. lamp nipple. The washer just barely fit in the bottle. I probably could've found some other washers which I would not of had to modify, but the store was closing and I didn't want to keep anyone after.
avfuelerict
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Re: Methods for making Robinson Coupling

Post by avfuelerict »

Drake Stutesman wrote:Being the 15 year old i am i had made a three bottled rocket like this one and got about 300 feet of air. my next project i made a 6 bottle 12 liter one of these and all the rocket had done was shoot up about six feet and hover there for 3 seconds??? im thinking i should try a different coupling any ideas?
In my other thread, air command recommended this http://www.aircommandrockets.com/construction_6.htm for a glue mixture for splicing bottle together. They also have a great video turtorial on splicing at .
I hope this helps. I have seen where many more advanced "engineers" of large rockets actually use staging to acheive higher heights. I have no experience whatsoever with this though.
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Brian
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Re: Methods for making Robinson Coupling

Post by Brian »

air.command wrote: The only rubber washer that is sealing the coupling is the middle one. The other two don't seal as air will escape past them through the thread. So technically you don't need them, though it's still a good idea to use them to protect the bottle from the sharp edges of the metal washers.

- George
I was testing a PVC coupling with one o-ring between a bottle and lid and it leaked. Im unsure if it was the o-ring but the I'm thinking of testing with 2 soon.
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air.command
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Re: Methods for making Robinson Coupling

Post by air.command »

Brian wrote:I was testing a PVC coupling with one o-ring between a bottle and lid and it leaked. Im unsure if it was the o-ring but the I'm thinking of testing with 2 soon.
Where was the o-ring? Was it around the thread of the bottle, or was it squished between the bottle and the cap? Squishing o-rings between two flat surfaces does not work very well. You need to use a flat washer for that. O-rings need to sit in a groove to function properly as they are designed to deform under pressure in order to seal. Do you have a photo/diagram of the PVC coupling, it would make it easier to discuss without guessing.
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Brian
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Re: Methods for making Robinson Coupling

Post by Brian »

This pic should help!
16mm and 20mm OD pipe
16mm and 20mm OD pipe
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I'll be sure to try inner tube washers because the o-rings arn't very compressable and don't seal the irregular surface.
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