Kevlar question

[prowlerguy]

OK, I need help. I have been having a problem with my Kevlar shock cord on my Wizard that I am using for my NARTREK Bronze. It has frayed and seperated twice, sending the nosecones and parachutes into another time zone (luckily, I have recovered the body both times). The first time the Kevlar broke where I had tied it to an elastic shock cord. I had used CA on the knot, and since I later read that you should never use CA like that, I assumed that was my problem. I repaired it to use nothing but Kevlar thread (no elastic) and white glue on the knot on the nosecone, but it again broke at the knot on the nosecone fitting. I am using size 207 (.025", 90#) from McMaster-Carr, which should be a plenty for a light Wizard. What is my problem?

 

[jflis]

I would assume that you either have too tight a knot (knots weaken any sort of cord, even Kevlar), or too short a length.

Also, are you sure you have "Kevlar"? Kevlar is a trade name and patent of DuPont. There are many knock off threads out there that look the same but *aren't* kevlar...

 

[Stymye]

also avoid tieing it with a simple overhand knot .the thread can actually cut itself ,use a surgeons knot

https://www.killroys.com/knots/surgeon.htm

 

[jflis]

Another recommended knot if you are tieing two dis-similar or different diameter items together is the Nail Knot: https://www.flymartonline.com/article212.html

 

[rbeckey]

Perhaps kevlar thread is not sufficient. I use heavier string type kevlar from Pratt Hobbies. Try TK Mini or TK Microbraid. I use these and have yet to have one fail.

 

[flying_silverad]

Kevlar as Jim has said comes in several knock off modes. One problem with all of them is whether or not they are bonded. Bonding the thread helps keep it from fraying but also may have some bearing on whether or not a knot (did I just say that ) will hold if it's glued.
I switched over to .O35 in all my kits and have had zero neg feedback. Before you go spending a lot of money, I could send you 10 feet of 0.035...see if you like it. Free.
Just Email me and let me know.

 

[prowlerguy]

Thanks for all your input. After reading them all, I am leaning toward trying a different knot arrangement.

I am pretty sure it is really Kevlar, since McMaster-Carr is a pretty reputable firm and they identified it as Kevlar. I am pretty sure that the thread is thick and strong enough because a) my Wizard is VERY light and b) I have used this same thread in all my other rockets in a more conventional lead-out from the MMT with a zero failure rate. This leaves me with my choice in knots, which I believe included an overhand knot. Thanks again for all your help.

BTW, I am really looking forward to my first FlisKits ever (a Duece, Tres, and ACME).