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  #1  
Old 10-30-2015, 01:35 PM
aeppel_cpm aeppel_cpm is offline
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Default Making tubing couplers fit less tightly

I have a couple of examples of tubing couplers that I would like to fit less tightly. For instance, couplers on booster stages and couplers used as nosecone shoulders.

What are some good ways to reduce the OD without destroying the paper tubing?
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Old 10-30-2015, 01:39 PM
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Jerry Irvine Jerry Irvine is offline
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The only good way is to peel a layer of paper off. Some paper while fairly thick on the outside layer is itself a fiber that can be partially peeled by starting an edge with a sharp x-acto. I should note you should precut along the edge of the mating tube so the peel has a clean edge. Partially through the tube thickness only of course.

Two other ways are sanding, and getting it wet ,and literally rubbing some off since, again, it is just fiberous material. Clean up with a nail sanding board.

Jerry

Last edited by Jerry Irvine : 10-30-2015 at 02:26 PM.
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Old 10-30-2015, 01:44 PM
aeppel_cpm aeppel_cpm is offline
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I've thought about sending them before. But I was concerned that the ruffed up surface would degrade with further use.
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Old 10-30-2015, 02:01 PM
Rex R Rex R is offline
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sand to the size you want(usually doesn't take much), apply thin CA, then sand with 320/400 grit sand paper to smooth things out. if you're worried about losing strength, glue a piece of card stock inside your coupler.
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Old 10-30-2015, 02:14 PM
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hcmbanjo hcmbanjo is offline
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Quote:
Originally Posted by Rex R
sand to the size you want(usually doesn't take much), apply thin CA, then sand with 320/400 grit sand paper to smooth things out. if you're worried about losing strength, glue a piece of card stock inside your coupler. Rex


Rex is right!
Most of the red and brown couplers are plenty thick already.
Sand until you get the fit you want, apply CA only to the half that'll be exposed.
Sand the CA side smooth with 400 grit.
The rougher half that's glued into the nose cone or body tube won't be seen.
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Old 10-30-2015, 02:40 PM
Rex R Rex R is offline
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it gets tedious when you start getting into the 3" and larger diameters .
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Old 10-30-2015, 07:54 PM
stefanj stefanj is offline
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Reinforce, sand, and seal . . . then sand again.

I reinforce by soaking in Minwax Wood Hardener or coating with epoxy. For large couplers I've glue balsa stringers inside.

Sanding is obvious.

Sealing means coating the sanded surface with something to harden the surface fuzz.

Then sand again to "polish" the surface.

I don't peel if I can avoid it.
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Old 10-30-2015, 10:06 PM
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Sanding will help whatever glue you use in building the rocket to soak into the coupler better, making it much stronger whether it's white, yellow, or epoxy. The regular construction process will strengthen the coupler more than what little strength is taken away by light sanding. Soaking in CA or laminating the inside is overkill unless you have to peel away a considerable amount of the coupler. Many model rockets and most mid and high power rockets are way overbuilt.

Using them as slip fitting booster couplers or NC shoulders presents the need for "slicking them up", and CA with a little sanding does nicely there.
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Old 11-01-2015, 10:32 AM
aeppel_cpm aeppel_cpm is offline
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Thanks all, for the tips.

It sounds like CA is my friend.
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Old 11-01-2015, 10:38 AM
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+1 on coating half the coupler with CA and sanding smooth. I did a couple like that (Ranger, 29mm Mean Machine) and I didn't have to remove any layers - I just coated it with CA after gluing it into the payload compartment, let dry and sanded glass smooth. Worked really great!
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