Attaching shock cord to hollow nose cone

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Digit
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Attaching shock cord to hollow nose cone

Postby Digit » Tue Jun 21, 2016 8:29 pm

Anyone able to impart some knowledge regarding attaching a shock cord to a hollow nose cone?
It's a HDPE cone and all my epoxy packets are suggesting they won't bond to it.
Cheers
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Re: Attaching shock cord to hollow nose cone

Postby ogivemeahome » Tue Jun 21, 2016 8:38 pm

Carve a balsa plug that will fit snugly, 'key' the inside of the nose cone by scratching with a blade/course sandpaper on a stick, epoxy the plug in place, drill a hole through the nose cone/plug (sideways), insert a pin of some description (balsa, carbon fibre, hardwood dowel), fill and sand any irregularities, stress test to see what happens.
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Re: Attaching shock cord to hollow nose cone

Postby vance2loud » Tue Jun 21, 2016 9:11 pm

http://www.ausrocketry.com/forum/viewtopic.php?f=6&t=2699 3/4 of the way down the page shows foaming the shockcord into the nose.
http://www.jcrocket.com/plastic-nose-mods.shtml shows similar to what ogivemeahome suggested except adding noseweight mixed with epoxy rather than the balsa.
I quite often do like the John Coker video but insert a 6mm coach bolt or similar into the epoxy with the thread sticking out. It allows a m6 eyenut to be screwed on for recovery attachment and noseweight to be directly screwed in place if required.
I try to leave 40mm roughly sticking out to add washers or nuts to if required.
If you do similar always add a nut before the eyenut so you can lock them together to prevent it unscrewing.
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Re: Attaching shock cord to hollow nose cone

Postby OverTheTop » Wed Jun 22, 2016 7:02 am

If there is a step in the base of the NC where the coupler is you can make a disc of thin ply or fiberglass (or whatever) that is just bigger than the step inside the NC. Then flex the plastic NC to insert the disc and epoxy in place. The glue just holds the disc in place, with the step in the molding taking the force. Attach eyebolt or something to the insert.
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Re: Attaching shock cord to hollow nose cone

Postby cryoscum » Wed Jun 22, 2016 8:50 am

There are obviously many ways to do this and I suspect many of them work perfectly fine. This is my take for smaller (and not so small) plastic nosecones:
I drill a 5 or 8mm hole in the side wall of the shoulder through which you can work. Put a small eye bolt in there or a Kevlar loop knotted such that it cannot pull out. Then some epoxy to hold it in place. The hole in the side wall doesn't make any difference.
Something like this:
1.jpg
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Re: Attaching shock cord to hollow nose cone

Postby Digit » Wed Jun 22, 2016 11:09 am

Thanks for the info guys, a slight modification to that John Coker video looks like it might be an option. That is a lovely sketch thanks Nic but Maybe I was'nt clear when I said 'hollow', I've actually removed the bum to make the nose cone hollow. To explain I've drawn a picture too! :lol:
coollikenic.jpg
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Re: Attaching shock cord to hollow nose cone

Postby Digit » Thu Jun 23, 2016 1:51 pm

I think I will try this idea. anyone tried something like this and had success / failure?
cheers

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Re: Attaching shock cord to hollow nose cone

Postby cryoscum » Thu Jun 23, 2016 2:26 pm

Pinning it through will go a long way to help keep that epoxy "plug" in there, yes.
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Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
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Re: Attaching shock cord to hollow nose cone

Postby nils » Fri Oct 27, 2017 12:43 am

I have learnt that it is not only the HDPE itself that is unbondable. It is more about that the HDPE details are covered with release agent.
It is not possible to clean them just with solvent but with flame treatment + alcohol cleaning.
I tested this flame treatment + alcholol cleaning yesterday. I bonded polycarbonate fins to HDPE tube. Today I was not able to rip these fins off with my muscle power.

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Re: Attaching shock cord to hollow nose cone

Postby Oldboy » Fri Oct 27, 2017 11:42 pm

I think it sounds like you have had a win .
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Re: Attaching shock cord to hollow nose cone

Postby OverTheTop » Sat Oct 28, 2017 9:42 am

I have learnt that it is not only the HDPE itself that is unbondable. It is more about that the HDPE details are covered with release agent.
It is not possible to clean them just with solvent but with flame treatment + alcohol cleaning.


I had similar issues bonding CF sheet to an ABS printed part. Flame treatment worked well, but unfortunately only some of the time. The process variability put me off using it on anything other than the test sample and I went back to a more conventional material (G10 fiberglass) for the core of the fin.

Make sure you consider how robust and repeatable your process is in your own case.
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