mounting shock cord question

This kit I am building has very limited space to mount shock cord to 54mm MMT inside 2.5" BT.As seen in pix the centering rings are about 3/16" so my thought was to go with a 1/16" cable with loop,drill hole threw top of centering ring,run cable threw the hole and epoxy cable with blocks on end into one of the fin fillets or the side of MMT.

Will this work???:confused2: Or should I just epoxy a nomex cord to the BT in the upper end?This is a fiberglass kit so was worried if epoxied to upper inside of BT it might break away upon ejection after a few launches.

Any ideas or comments needed since I am a HPR noob after all.

THX

Sounds like a good plan to me. As long as the cable (stainless steel, right?) is strong enough to take the hardest shock that you expect that rocket to get. Lately I've been using 90 lb. stainless steel leader for some of my rockets, which are much smaller than yours (under 2" and built with paper tubing).

Yes sir its stainless.I'm not sure of the tinsel strength of the 1/16" cable.Was bought off cut to length spool at Lowe's and I looked but couldn't find its rating on label.:confused2:

Rocketeer Gator said:

...drill hole threw top of centering ring,run cable threw the hole and epoxy cable with blocks on end into one of the fin fillets or the side of MMT.

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A suggestion for a slight modification to that plan, if you will. Instead of running the cable through a hole in the centering ring, Dremel a small notch in the centering ring so that the cable will slip under the ring - then, go ahead and epoxy the cable down onto the motor mount like you planned. That way, it's the motor tube that'll take the brunt of any pull on the cord, and not the centering ring (which, when the cord gets pulled, might splinter throgh to the motor tube anyway).

You could look up steel rope or cable on the McMaster-Carr web site and see what the specification is if you can find something that matches what you have. The 90 lb. fishing leader wire that I have been using is about 1/32" in diameter.

MarkII said:

You could look up steel rope or cable on the McMaster-Carr web site and see what the specification is if you can find something that matches what you have. The 90 lb. fishing leader wire that I have been using is about 1/32" in diameter.

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I've used the McMaster material. Breaking strength is 450-500 lb. depending on construction. My preference is 7 x 19 strand core - best compromise between strength and flexability.

Well this is what I ended up doing.Centering ring was already epoxied so had to drill a 3/32 hole between MMT/ring.Pulled the cable threw then crimped the block on.Used epoxy clay to secure block to MMT.Then ran cable threw series of holes drilled at base of each fin wrapping cable entirely around MMT and epoxied in place.The thimble comes within 3" of top of BT so hooking regular shock cord will be easy and cable won't be able to zipper BT if there is a "hard" ejection.

Gator,

Is it me or is there a big chunk of epoxy and aluminum at the forward centering ring that you're gonna need to sand down?

Looks big enough that it might take you a while....

G.D.

gdiscenza said:

Gator,

Is it me or is there a big chunk of epoxy and aluminum at the forward centering ring that you're gonna need to sand down?

Looks big enough that it might take you a while....

G.D.

Click to expand...

Well its epoxy clay and the aluminum block crimped to cable but both have clearance of the centering ring by a cpl frog hairs.

I wish I had seen this before you glued the cable in place. I would have recommended against it. I did almost the same thing.

I build my L1 rocket with a cable. I just epoxyed it to the MMT. It was a 38mm MMT in a BT with a 2" ID. The wire has held up just fine! The problem is that it's not flexiable. I had to cut a notch in a dowel to allow grabbing and twisting and wrapping the cable so it will fit down into the BT. It's a PIA.

I really wish I had used 1/4" tubular Kevlar instead. Although it has held up just fine, I'll never use cable again in a small diameter rocket, less then 4".