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  #1  
Old 02-10-2008, 09:30 PM
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tbzep tbzep is offline
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Default Make Your Own Tube Coupler

This has come up several times when people needed couplers they couldn't find or just didn't want to place an order for a couple of couplers. Some folks don't think the couplers are strong enough. Some don't think they can be made round. It's easy to do, and I can make them just as round as the original piece of tube.

I know there seems to be a lot of steps here, but it's actually a very simple process.

1. Start with the same size BT you plan to couple together. Cut a piece of tube off at whatever length you want the coupler to be.

2. Cut it lengthwise and slip it inside the body tube so you can see how much it overlaps. Regular tubes can be easily cut with good scissors or with a hobby knife.

2.5. Draw a reference line inside so you will know how much you need to cut.

3. Cut off the overlap and safe the strip you just cut.

3.a. Some folks like to make the new coupler ends butt together perfectly. This is great when the cuts are perfect, but lends to whopsided (technical term) couplers if the cuts aren't near perfect.

3.b. I usually cut and leave a little gap. The gap can be taken care of later.

4. Gently spread the new coupler without creasing it so that it will want to expand slightly larger than its original diameter when you let it go. This will help you get a nice round coupler in the next step.

5. Put the new coupler material back inside the body tube (short scrap tube is best) and find the little strip you cut out of it. A regular strip of cardboard will work just fine if you lost the original strip or if it's too skinny.

6. Paint a little glue on each side of the new coupler.. You don't want glue to get down to the main body tube. This is one benefit to a perfect fit when you cut the slit, but I'd rather deal with the glue than to try to make a perfect cut.

7. Apply the strip and make sure the new coupler is spread apart and touching the scrap body tube all the way around on both ends.

8. Let glue dry.

9. (Optional) Add thin CA on the inside if you want a stronger and stiffer coupler. (coupler on left in the pic has some CA in it.)

10. (Optional) Put some Fill-n-Finish or Bondo putty in the outside gap if you want a perfectly slick outer surface for special applications.

Photo: As you can see, the left coupler is in the little piece of scrap BT that let me inspect the diameter of the new coupler as the glue dried. This let me make a perfectly round (as round as the BT anyway) coupler. I used some scrap cardboard to glue the coupler on the right because I lost the little strip I cut from the tube. In a perfect world, the strip is best to use because it has the curve of the BT in it already. Coupler on the right has the little gap filled by Fill-n-Finish. My hands were dirty and discolored the goop so it doesn't look like it's filled in the pic, but it is nice and flush.


Last edited by tbzep : 02-12-2008 at 09:11 PM.
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Old 02-12-2008, 03:35 PM
Breeze1913 Breeze1913 is offline
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Cool. I needed that.

Thanks for taking the time to post this, and take the pictures. As usual, a picture is worth a thousand words.
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Old 02-12-2008, 06:45 PM
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Dave,

Really nicely done. You're right, it does come up often and your how-to is a great reference.

The only additional thing I do that you didn't mention would come between step 2 and 3.

After I have slid the cut piece inside, I stick a pencil in at an angle and mark the edge where the coupler-to-be overlaps itself. Then when I take the piece out I have a nice line to show me where to cut.
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Old 02-12-2008, 09:10 PM
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Quote:
Originally Posted by Gus
Dave,

Really nicely done. You're right, it does come up often and your how-to is a great reference.

The only additional thing I do that you didn't mention would come between step 2 and 3.

After I have slid the cut piece inside, I stick a pencil in at an angle and mark the edge where the coupler-to-be overlaps itself. Then when I take the piece out I have a nice line to show me where to cut.


Gotcha.

Edited to add step 2.5.
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Old 02-13-2008, 07:49 AM
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Excellent tutorial! I've made it a sticky.
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Old 09-25-2008, 03:27 PM
marcsl marcsl is offline
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A similar process is described here :

http://www.rocketrytoday.com/coupler.html

It also has a little calculator which will tell you how much needs to
be cut, instead of step 2 in this tutorial.

Marc
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Old 09-25-2008, 11:40 PM
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Quote:
Originally Posted by marcsl
A similar process is described here :

http://www.rocketrytoday.com/coupler.html

It also has a little calculator which will tell you how much needs to
be cut, instead of step 2 in this tutorial.

Marc


It's a lot easier to slip it in and mark it like mentioned in step 2.5.
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Old 06-24-2011, 07:15 PM
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I started making these inch and a half to two inch couplers after your tutorial (THANX) and only will add that on the rare occasion I am off a bit, experiment with overwrapping the finished (too small) coupler. I find best result with a single butted joint overwrap with whichever paper thickness best fills the need, rather than multiwrapping thin paper. I have used everything from cash register remnants (ultra-thin) to cardstock (on a big oops). Single wrap means limiting glue needs and no ply failures.
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Old 04-21-2013, 11:45 AM
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K'Tesh K'Tesh is offline
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Thumbs up Nice way of recycling....

Nice!

I cut out two 5" payload section and two 2 3/4" booster sections from a BT-60, and this will allow me to use the remaining scrap. Also, if you have an old damaged tube, you could put this to work with that.

Thanks!
Jim
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Old 04-13-2014, 11:34 PM
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It helps to sand the glassine coating off the coupler for a better bond, and if you are repairing a previously flown model, make sure to clean all the black powder residue out of the airframe as well. Glue doesn't like BP...
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