Attaching Shock Cords to Eye Bolts

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lcorinth

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I'm building an Estes Leviathan, and have decided to attach the shock cord to the forward centering ring via a forged eye bolt. I bought 25 yards of nylon webbing to use as shock cord material for a few rockets.

I have read of a couple different methods of attaching a shock cord to an eye bolt, and wanted to get some feedback from you guys. A couple methods I'm considering are sewing the end of the shock cord to the main part, or epoxying it.

The sewing method seems pretty labor intensive, especially since I'd have to do it by hand (no sewing machine). I feel like the epoxy method might be a better option. Currently, I'm working with Bob Smith's 30 minute epoxy.

What do you guys think about this? Sewing or epoxy? Or is there another method I should go for?

Thanks!
 
Try the PML method. PML>Webstore>Recovery>PML recommended way of tying tubular nylon. Sorry don't remember how to embed links right now.
 
I always sew my harnesses/shock cords, the epoxy creates a hard area that will eventually break and may even chemically attack the harness material.
 
One method I've developed for my rockets that have eye bolts next to the motor mount is to use a length of Kevlar that is 2X the length of the inside of the body tube plus a little extra. I then tie loops on both ends in such a way that keeps the Kevlar just a little short of the front of the body tube after threading the length through the eye bolt. I tie the remaining shock cord material (elastic, parachute cord, tubular nylon, etc) to the loops. This way I can inspect the Kevlar easily, and replace it easily if necessary. I only use this method on rockets that are too short to fit a baffle.

[EDIT] Adding image per request (below) to show what method I use.
 
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One method I've developed for my rockets that have eye bolts next to the motor mount is to use a length of Kevlar that is 2X the length of the inside of the body tube plus a little extra. I then tie loops on both ends in such a way that keeps the Kevlar just a little short of the front of the body tube after threading the length through the eye bolt. I tie the remaining shock cord material (elastic, parachute cord, tubular nylon, etc) to the loops. This way I can inspect the Kevlar easily, and replace it easily if necessary. I only use this method on rockets that are too short to fit a baffle.

K'Tesh, would you mind posting a picture of this? Thanks in advance!
 
I've used K'Tesh's approach a few times recently and been pretty happy. If I'm not going to do that for whatever reason, tying a bowline is the way to go.
 
I tie a square knot, leaving a loop to attach quick-links or other lines to.
Make knot tight and leave 2+ inches of tail (harness end).
Then wrap knot and tail (to main harness) TIGHTLY with yellow masking tape.

I prefer to use Kevlar over Nylon as it is more fire resistant, but this method works for both.
Done 100+ times with no knot failures, including projects up to 40lbs.
Can be prepped, modified or repaired quickly.

1/2" tubular Kevlar, 1/2 Nylon, and 7/16" Kevlar strap pictured.

Using flame to prevent nylon from fraying works well.
For Kevlar, I just wrap exposed ends with tape.

ALWAYS carefully inspect all parts of rocket before every single flight, including harness components.
After many (5 to 10+) flights it may be necessary to replace or add tape.

20150913_115506.jpg
 
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I'm building an Estes Leviathan, and have decided to attach the shock cord to the forward centering ring via a forged eye bolt.

This is rated as a 17oz kit.
A forged eye-bolt is a lot heavier and stronger than needed.

The smallest U-bolt you can find at the hardware store will give you a much lighter, solid metal attachment point.

I prefer U-bolts to eye-bolts for recovery attachment:
They are all loop, without the wasted weight of the base of the eye-bolt, and have two points at which they attach to the centering ring.
 
Another option to consider is to find a seamstress/tailor who can do the sewing for you. They may charge you a little bit (probably no more than $10, but don't quote me). Try looking at a dry cleaners/laundromat for the seamstress. The one I used to use before she retired would sew the patches on my Den Leader's uniform for a good conversation. If you find someone, you can even ask them to use Kevlar thread (65# would be good) if they didn't mind. Of course you would supply the Kevlar.
 
Unless the rocket is extremely overbuilt, I would just use a LOC style loop mount. I epoxy the loop in, then add a layer of glass cloth over it for strength, and, to smooth it out so the recovery gear doesn't snag. The problem with an eyebolt in a rocket of this diameter, is being able to get in there to replace the cord if needed. Myself, I can not reach into any thing under a 4" tube, and even then, if I tense my fore arm muscles, my arm gets stuck. Smaller tubes, I would need to use a coat hanger, or some kind of wire to fish the cord through the eye bolt.

For making loops in the nylon shock cord, I would avoid securing the loops with epoxy, especially Bob Smith brand. Smith brand epoxy, without any kinc of structural filler, is brittle when dry. It's great on Low/Mid power, and, any joints that won't see any flexing, and that don't rely solely on the adhesive for strength.
 
The sewing method seems pretty labor intensive, especially since I'd have to do it by hand (no sewing machine).

I sew all of my shock cords. You can get a sewing awl at Harbor Freight for less than $10, and it is not that difficult. I use an X pattern to allow some flex in the stitching.
 
K'Tesh, would you mind posting a picture of this? Thanks in advance!

Done...



I've edited it into my original post to the thread too.

Currently, I've got a fishing swivel acting as a place holder for the loop that will eventually tied into it. I also haven't trimmed the extra off the end of the loop.
 
The smallest U-bolt you can find at the hardware store will give you a much lighter, solid metal attachment point.

I prefer U-bolts to eye-bolts for recovery attachment:
They are all loop, without the wasted weight of the base of the eye-bolt, and have two points at which they attach to the centering ring.

I like the ubolt idea also. You can get some pretty small and economical ubolts by taking a cable clamp apart and throwing the clamp part away....

IMG_3839.jpg

index.jpg
 
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I like the ubolt idea also. You can get some pretty small and economical ubolts by taking a cable clamp apart and throwing the clamp part away....

VERY Interestink!!!

[video=youtube;krD4hdGvGHM]https://www.youtube.com/watch?v=krD4hdGvGHM[/video]

I vil use dis...
 
I use Quik-Links for everything. They're cheap, replaceable, and don't weigh very much.
 
Done...



I've edited it into my original post to the thread too.

Currently, I've got a fishing swivel acting as a place holder for the loop that will eventually tied into it. I also haven't trimmed the extra off the end of the loop.

This is pretty close to how I've been doing it, too. Works pretty slick, and nothing a dowel with a hook on it won't cure for getting a new one in place if the original breaks.
 
Over the years, I've become much more conscience of weight added to my rockets. I now use a piece of Kevlar epoxied to the MMT on each side and forming a loop that extends a couple of inches out of the booster BT. I usually use a piece of 1/2" Kevlar mule tape for this when the rocket is going to be under 20 lbs. I will use a 9/16" tubular Kevlar if it is going to be heavier.

I've found that Kevlar epoxied to the MMT is a very solid anchor. It also tends to be lighter then adding metal u-bolts or eye-bolts, welded or forged.

For those older rockets that have u-bolts or eye-bolts, tying the shock cord to a quick link works just fine. Like delta22, I tape over anything not metal to protect it from ejection gases.
 
ImageUploadedByRocketry Forum1442455296.413013.jpgImageUploadedByRocketry Forum1442455330.820584.jpg
Loop through square not with a little shrink tubing, easy to change quickly.
 
I like the buntline hitch, tied to a small u-bolt. I wouldn't run nylon all the way down to the top CR, without a kevlar wrap, too high a chance it'll get hit with burning BP. I learned this the hard way. The LOC loop is also a very reliable method, and keeps the nylon well away from the ejection charge.
 
I used to use a slip knot to tie-off shock cords, but now I use a Halyard hitch. I find it compact and doesn't require the use of masking tape. It works well with eye-blots, U-bolts, and inline swivel connections. The knot tightens on itself with increasing tension.

halyard_hitch.jpg
 
That is most definitely a figure-8. I've done climbing rigging in the past.

And yes, it's one of my favorite knots.
 
That is most definitely a figure-8. I've done climbing rigging in the past.

And yes, it's one of my favorite knots.


If you look at how the figure-8, it sure seems to follow the way a Bowline is tied.

The Rabbit comes out of his hole, around the tree, and back into his hole. The only difference seems to be that "the Rabbit" is a loop rather than the end of the rope.
 
If you look at how the figure-8, it sure seems to follow the way a Bowline is tied.

The Rabbit comes out of his hole, around the tree, and back into his hole. The only difference seems to be that "the Rabbit" is a loop rather than the end of the rope.

Other than being "... a method of fastening or securing linear material such as rope by tying or interweaving." I'm not seeing the similarity either. But I've always said (and I'm sure others have too) "You can't argue with a Klingon." :wink:

We're knot going to argue about this, are we?

You have to ask ? It's what we do here ! :grin:
 
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