How to tie fat shock cord to skinny shock cord

DirkTheDaring

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The Fliskits Tres 24 comes with one of those really fat shock cords to attach to the nosecone and parachute, and skinny kevlar shock cord that attaches to the engine mount. What is the best way to tie these very different cords together? See photos.

Thank you.

PS - cross posting in the Fliskits thread.
 

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lakeroadster

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The Double Sheet Bend uses a second turn around the thicker rope. It is recommended when there is a great difference in the diameters of the two ropes.

Pretty sure the OP's example qualifies as "great".

Double Sheet Bend.jpg
 
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mjennings

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Sheet bend is good, not saying it's better I'm not a knot expert, but I've used square knots on lighter rockets, and 2 bowlines (the loop of the bowlines pass through each other) with success.
 

boatgeek

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I'd use a double sheet bend there (note: big line is blue, small line is red in @lakeroadster 's example above). For shock cords, I usually put a dab of white glue on the knot as well. That helps keep it from loosening, particularly with slippery line like Kevlar. White glue is flexible enough that it doesn't make hard points in the line that make it fail prematurely.
 

DigBaddy

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In these cases I tend to add a swivel, then improved clinch knot for both lines. if no swivel, then a perfection loop on the kevlar and then improved clinch on the larger/elastic to the loop.
 

neil_w

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With Kevlar and elastic, I first tie a loop in the Kevlar (any old way, doesn't matter) and then thread the elastic through like this:
1660750681276.png
When pulled tight it is fantastic. There is tremendous friction in the joint, and I've seen absolutely no tendency to loosen.

I don't know if it would work as well with the material shown in the first post here.
 

DirkTheDaring

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Thank you all! The sheet bend or double sheet bend is what I was looking for. I had a vague memory from my rather short career as a boy scout, but I kept coming up with sheepshank, which I know isn't the right one.

I'll dab the glue and be using swivel hooks. I use them everywhere, even my swivel hooks and swivel hooks.

Thanks again!
 

Lee

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If you want your shock cords to be detachable, use a barrel swivel on one cord and a 75 lb test Tacticle Angler Clip on the other. I use this combo when tossing lures for striped bass in the surf. Low profile, light weight and strong as .....
 

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DarthMuffin

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If you have some heat shrink tubing that will fit, I'd use that instead of a drop of glue on the knot. Will keep the ends from fraying too and smooths out the area some so it doesn't catch on things.
 

DirkTheDaring

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If you have some heat shrink tubing that will fit, I'd use that instead of a drop of glue on the knot. Will keep the ends from fraying too and smooths out the area some so it doesn't catch on things.
I’ve been doing both. Belt and suspenders. Properly placed I think it protects against at zippering as well.
 

Steve Shannon

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Sheet bend is good, not saying it's better I'm not a knot expert, but I've used square knots on lighter rockets, and 2 bowlines (the loop of the bowlines pass through each other) with success.
This isn’t really a critical application, but square knots are not recommended for tying two rope together.
 

smstachwick

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This isn’t really a critical application, but square knots are not recommended for tying two rope together.
Interesting. Looks like old BSA handbook got it wrong, and the new editions probably still are. Demonstrating the ability to tie it was even a joining requirement because it’s allegedly a “joining” knot.

I’m going to have to practice my sheet bends and bowlines now.

(Minor edits)
 
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neil_w

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This isn’t really a critical application, but square knots are not recommended for tying two rope together.
I can say, though, that when joining Kevlar to elastic, with no loose ends to be pulled sideways, it works well. Absolutely no slip, largely due to the friction-y nature of the elastic. This is for LPR use only.
 

DirkTheDaring

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Interesting. Looks like boy old BSA handbook got it wrong, and the new editions probably still are. Demonstrating the ability to tie it was even a joining requirement because it’s allegedly a “joining” knot.

I’m going to have to practice my sheet bends and bowlines now.
Me too!
 

DirkTheDaring

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This isn’t really a critical application, but square knots are not recommended for tying two rope together.
i use square knots because they're the only knot I remember, but I'm strictly low power, so lightweight. Plus a dab of CA and some heat shrink. But with my Tres 24, which is by far the biggest rocket I've built, I'm going to go with the recommended sheet bend.
 

dr-ws

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If you want your shock cords to be detachable, use a barrel swivel on one cord and a 75 lb test Tacticle Angler Clip on the other. I use this combo when tossing lures for striped bass in the surf. Low profile, light weight and strong as .....
Such pretty knots, and ideas for them abound!
I like this (Lee's) response the best, because of the [barrel] swivel suggestion, with its metallic connection/intervention in the line. I've little doubt many/most of the other suggestions will work just fine, UNTIL THE KEVLAR CUTS THE OTHER ROPE/ELASTIC.
BTW, I like a steel leader on a swivel for [especially musky] fishing, too - the muskellunge's teeth are almost as effective as Kevlar. . .
 
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