Shock cord attachment

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Brendans

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I remember rockets that came with a rubber band shock cord and I would pierce the body tube in two places about .25" apart with an xacto and then feed the shock cord through and apply glue? I seem to recall this but don't recall if this was a hack or SOP. Thx

Brendan
 

David Schwantz

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I think most were the little Estes trifold device. I have done the slit the tube thing when the other failed and I still HAD to fly again :)
 

KennB

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I recall the two-slit method being in some of the Estes kits from the late '60's. I think it may have included a piece of gauze over the exterior on some builds.
 

RocketTree

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I have cut a few rockets apart to reuse the tubing, and those Estes tri-fold mounts are really hard to remove!! Very surprising. Have not come across the body tube slit method before. Maybe before my time.

All my rockets builds now get kevlar leader attached to the motor mount, and shock cord attached to that. Easier to replace the cord later, when necessary.
 

Brendans

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I recall the two-slit method being in some of the Estes kits from the late '60's. I think it may have included a piece of gauze over the exterior on some builds.
Thanks. At least I'm not imaging it.

Brendan
 

kuririn

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My first kits were the Centuri Honest John and Defender, and they had the two slit method for attaching the shock cord.
Then some genius invented the tri fold anchor and that was the end of it.
A better mousetrap, as the saying goes.
 

tsmith1315

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My first HPR kit was a 4" from LOC. I was surprised to see an adaptation of the trifold mount- a loop of heavy nylon twine anchored with a generous blob of epoxy. I thought, "Really?". Made me nervous for a while, but it's still there 25 years later.
 

hcmbanjo

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I remember rockets that came with a rubber band shock cord and I would pierce the body tube in two places about .25" apart with an xacto and then feed the shock cord through and apply glue? I seem to recall this but don't recall if this was a hack or SOP. Thx
Brendan
This is probably what you were thinking of, copied from an old Estes instruction sheet:

Shock Cord Anchors 0874 2.jpg
 

jrap330

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I remember rockets that came with a rubber band shock cord and I would pierce the body tube in two places about .25" apart with an xacto and then feed the shock cord through and apply glue? I seem to recall this but don't recall if this was a hack or SOP. Thx

Brendan
with my first Centuri kit around 1971, that was the method, and my reaction was " what the..." Of course , as all first rockets it was lost to the winds. It was a 2 stager.
 

Brendans

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I preferred the Centuri kits back then. I didn't see the folding tab until I introduced my offspring and reintroduced myself to rocketry in the 80s
 

Woody's Workshop

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I've considered using 1/8" launch lugs that come in 12" lengths glued to the inside of the air frame from the top of the EM to the nose cone shoulder and threading the kevlar though it from the EM.
It would make sure nothing was exposed to ejection charge heat or flames above the wadding.
Attach a double loop end swivel between the kevlar and elastic.
 

jrap330

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I remember that from about 50 years ago--the cutting into the body tube, that is.
Yes, 1971 is 50 years ago, so you are right and I am old! As for Woody comments, might be a little tricky to fish shock cord through lugs. Probably have to start at top , fish out back end, attached to motor mount and glue in the mount.
 

Nytrunner

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The estes pathfinder rockets use a double slit for their shock cord too. Quick to instruct kids in, 1 less opportunity to glue fingers
 

JStarStar

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I always hated the tube-slit method of shock cord anchoring so i used a version of the "shock lock" method G. Harry described in early editions of the Handbook.
Instead of the bulky trifold method which could hang up the laundry going out (especially on BT-20
or smaller) you simply cut a piece of scrap body tube about 3/4" square, cut two slits in that piece, thread your shock cord through that, then glue the whole kaboodle to the interior of the tube.
The curvature of the scrap of body tube will allow it to conform closely to the interior of the rocket airframe. Use enough glue to cover both slits then press it down firmly with your fingers and allow to dry.
 

jrap330

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I always hated the tube-slit method of shock cord anchoring so i used a version of the "shock lock" method G. Harry described in early editions of the Handbook.
Instead of the bulky trifold method which could hang up the laundry going out (especially on BT-20
or smaller) you simply cut a piece of scrap body tube about 3/4" square, cut two slits in that piece, thread your shock cord through that, then glue the whole kaboodle to the interior of the tube.
The curvature of the scrap of body tube will allow it to conform closely to the interior of the rocket airframe. Use enough glue to cover both slits then press it down firmly with your fingers and allow to dry.
That is what I do, but not scrap body tube instead I use card stock, index cards , card stock base advertisements that you receive in mail etc.
 

JStarStar

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That is what I do, but not scrap body tube instead I use card stock, index cards , card stock base advertisements that you receive in mail etc.
Yep, pretty much any cardstock-type paper will do. I got into the habit of using body tube scraps because they were pre-formed in curvature to match the interior of the tube.
 

K'Tesh

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I think that unless it's a minimum diameter build, I suddenly get the urge to enter some flight competition, or I'm building a period accurate build for a prop (think making a movie (yes, I have a period movie idea in my mind)), I'd likely just use Kevlar and run it down to the engine mount. I'd still use the rubber for the portion that protrudes above the body tube. I would not, however, glue the Kevlar to the motor mount. I'd want to be able to pull it down and inspect it for damage.. A loop, that perhaps gets tacked down with a single drop of glue, would make sure it stays put.

For more on Rubber and Kevlar shock cords, I'd recommend people check out this thread...


And one other shock cord related thread....

 
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K'Tesh

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Yep, pretty much any cardstock-type paper will do. I got into the habit of using body tube scraps because they were pre-formed in curvature to match the interior of the tube.
Cardstock can be problematic when you're working with BT-5 or BT-20 minimum diameter kits though. ordinary copy paper (such as a scrap from junk mail) works fine for the smaller LPR rockets.
 

David J

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Original Estes WAC Corporal (K-11) used the slit tube method. It was one of my first (and still favorite) rockets. My second one was the V-2, it had a piece of gauze glue to the BT. Third build was Big Bertha, IIRC it was the first paper fold I built. Good Times!
 

MidOH

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Small diameter rockets, I still use the Estes trifold. But with Kevlar.

CA the kevlar string to the paper. Let dry. Soak in wood glue, fold it up. Then use a dowel rod to shove it as far down the tube as possible. Press it flat and round by rolling the dowel rod. I leave the kevlar a few inches longer than the tube, and tie the rubber shock cords to it.

Shouldn't ever hang up the chute or streamer, because those stay way above the cord mount.

Larger kits I put the kevlar on the motor tube. Two drops of CA to hold it in place, then coat with epoxy.

Bt20 fiberglass kits. I CA to the inside of a ring, then epoxy the ring half way down the tube.
 

jrap330

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Kevlar longer than the body tube, you do not do anything to mitigate the zipper?
 

kuririn

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CA the kevlar string to the paper.
Larger kits I put the kevlar on the motor tube. Two drops of CA to hold it in place,
Never use CA on kevlar, it makes the fibers brittle and prone to breakage:
How do you terminate Kevlar cord? | Page 2 | The Rocketry Forum
"Wood glue will stop fraying Kevlar. CA will run up the line and make the Kevlar brittle."
Shock chord idea. | The Rocketry Forum
"Be aware that CA isn't the best choice for Kevlar, as it tends to make it brittle and wear."
Other solutions for keeping your nose cone weight in place. | The Rocketry Forum
"CA wicks into the Kevlar and makes it hard, not what you want in your shock cord."

My preferred method is to tie a kevlar leader to the motor tube behind the forward centering ring. Cut a notch on the inside or outside edge for the leader to pass through the ring. Secure the knot and loop with wood glue. For MD rockets cut a notch on the thrust ring and tie a loop and knot with a kevlar leader on the ring. Again, secure with wood glue to prevent unravelling. Terminate the leader just below the end of the tube to prevent zippering and attach an elastic shock cord.
If you want to go the extra mile you can install a removable/replaceable kevlar cord. Google for links.

The two slit method is obsolete, like gauze for joint reinforcement, flash bulbs for charge ignition and fuses for upper stage ignition.
 
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MidOH

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I guess I should clarify. The CA is thick Gorrilla. It ain't wicking through anything. Just a small dot to keep the kevlar stationary so that the epoxy or wood glue can dry.

I CA the inside of the top of the paper tubes to reduce wear there. I'll also CA the bottom inside of paper motor tubes if using tape rings on motors.
 

kuririn

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I CA the inside of the top of the paper tubes to reduce wear there.
Good idea. Also helps prevent zippering. And masking tape on the kevlar line at the contact point.
I'll also CA the bottom inside of paper motor tubes if using tape rings on motors.
Might want to do the same to the bottom outside to prevent the tape from pulling up the paper.
Cheers.
 
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