What would be the best upgrade from a 1/4" elastic shock cord?

Kevlar only? Nylon only? Combination of kevlar and nylon? Woven? Tube?

What would be the best length?

If for replacing the 'rubber band' shock cord found in Estes kits I use threaded nylon cords..You can get them in various widths(1/8" up to 5/8") at WalMart in the crafting section. A package will have usually 6 to 9 yards for about a buck.

The best length? As much as you can fit in the rocket! But, generally, the rule of thumb is 1.5 to 3 times the length of the rocket..

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For anything above BT-60 sized rockets, I like to use about 5+ feet of black tubular elastic cord that Semroc sells, along with a braided kevlar strap of the appropriate length. BT-60 and BT-55 I like about 4 feet of the same. Less than BT-55 I use the old style flat elastic cord. I never use that "rubber band like" guff. Good for nothing but eventual breakage.

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When getting back into rocketry, I ordered a shock cord just to see what it was (being used to rubber bands). When I got it in the mail, it was exactly what you will find in the sewing section at Wal-Mart...

For smaller rockets using up to 18 mm motors (especially minimum-diameter rockets), elastic cords aren't necessary. Using 20" to 24" of Kevlar cord or cotton twine is sufficient.

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Thank you everyone for the replies.





After checking at walmart and a few fabric stores, all I found were elastics made out of rubber and polyester. Research says to get rubber and cotton for use as a shock cord in a rocket (polyester melts; cotton does not). But I can't find elastic cord made out of rubber and cotton. Asking for cotton only brings blank stares from the sales people.

Where can I get elastic material made out of rubber and cotton? Or is that why it's so cheap to buy it at a local store instead of from a rocket supply source?

In an admittedly very brief online search, I found this Rhode Island Textile 1/4" wide and 3/8" wide flat cotton/rubber elastic cord (see: http://www.createforless.com/Rhode+...l/pid36743.aspx and http://www.createforless.com/Rhode+...&utm_medium=cse ). Rhode Island Textile's South Carolina Elastic Division (see: http://www.scelastic.com/ ) makes their elastic cords, and they may also make 1/8" wide flat cords and round elastic cords. Below are the product descriptions from the vendor web site.

1/4" cotton/rubber elastic cord description: "Unaffected by chlorine and salt water, this elastic is great for swimwear, and other wash and wear garments. 1/4" 150yd Natural - 76% cotton, 24% rubber"

3/8" cotton/rubber elastic cord description: "Unaffected by chlorine and salt water, this elastic is great for swimwear, and other wash and wear garments. 3/8" 100yd Natural - 65% cotton, 35% rubber"

I just e-mailed the Rhode Island Textile home office and their South Carolina Elastic Division for information on 1/8" wide (flat), 1/4" wide (flat), 1/32" diameter (round), and 1/16" diameter (round) cotton/elastic cord, and I will post their reply when it arrives.

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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

Thank you blackshire for your find and the links.

Checking into it....

A minimum order of 150 yards is required for an order of the 1/4" cotton-elastic. Including shipping ... it comes out to about $42. The local stores have packages of 10 yards of the polyester-elastic for $2 to $3 dollars. A 10 yard package of the cotton-elastic should be about the same cost (if one could find it). 10 yards should be enough for a half dozen rockets. That leaves $39 of material (from the 150 yard roll) sitting on the shelf for a long time. Not cost effective.

Seems like the only place to get 10 yards of the proper 1/4" elastic material might just be only from a rocket supply center these days.

You might find what you need here

Shock Cord Material

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Yes, polyester can melt, but I can tell you for a fact, cotton covered elastic shock cords will get some nasty burns from BP particles landing on them as well... Cotton won't melt, but it WILL burn, and it will eventually give out anyway as the fiber frays...

I just go with the regular polyester sewing elastic and replace it when the cord gets gnarly...

Cheap and effective... OL JR

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