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Loose couplers...

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firemanup

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Been going over my Binder Jag yesterday and today getting ready for this weekends launch and i've come to decide that the couplers are too loose for my liking..

What's the best way to fix this..?? This is a long rocket and the coupler going into the booster section is the worst one, you can "bend" the rocket quite a bit between there and the nosecone which isn't a good thing...

I've tried coating it one time in 30 min epoxy and can't see that it's helped much, however it does give me a better surface to apply masking tape to.

I can apply masking tape and get a good tight fit that alleviates any of the rocking caused by the loose coupler, but then it's a bear to pull out and i'm worried about ejection not seperating the pieces..

I'm assuming the best would be to keep applying layers of 30 min epoxy..??

The other problem is heat, out in the sun i noticed several rockets last launch getting tighter.

Would shear pins be another option...?
 

powderburner

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I am definitely not a high-power construction expert, but to tighten loose fits like you describe I have used laminates of typing paper. I tacked the first edge lightly with CA, let it get good and set, then squirted a good bit under the paper and wrapped quickly, working the CA underneath to spread out. I used a piece of glass (my desk-top cover) to roll the piece (I was building up a section of BT) with the largest wooden dowel I could fit inside.
After all that CA cured, I put a bit more around the edges of the paper to make sure it would stay put, and then sanded lightly. For my project, I had to laminate quite a few sheets to build up the thickness I wanted, and if you get in a hurry with lots of layers it can end up lumpy, so be careful of that.
I would be afraid that a thick layer of epoxy might get a little sticky after a hot day in the sun. Maybe you might want to cover your epoxy with some tissue paper?
 

edwardw

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I have done the same thing as powderburner, but I use 3M's spray adhesive to get it tacked down and tight fitting. Then I coat it all in epoxy to harden it.

Edward
 

Stymye

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cut a split in the coupler lengthwise stretch it a little than glue
fill the gap if necessary
 

daveyfire

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Shear pins are definitely an option. If you've added resin to your couplers they should be strong enough, I would suggest two 2-56 screws or tiny styrene rods on opposite sides. Just tighten it up enough to be snug using masking tape and then install the pins. Be sure you have enough ejection charge to pop them (a ground test is in order here...) and you're good to go! I started using shear pins a year and a half ago and haven't looked back since :)
 

BHP

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McMaster Carr has the 2-56 nylon screws you need, Firemanup. Order the pan head phillips style (easier on the thumb when pushing them in place) in the length you may think you'd need to get through your BT and coupler.

http://www.mcmaster.com/asp/DisplCtlgPage.asp?ReqTyp=CATALOG&CtlgPgNbr=2892&CtlgEdition=&sesnextrep

They come in bags of 100 and in black or white. Order lots of 'em to reduce your average shipping costs!

On two different occassions I've ordered from McMaster by 10:00 a.m. and had the package by noon the next day via UPS. You order tonight and you'll have them by Friday, I'm sure, since you're also in the Great State of Iowa. ROL's InfoCentral has a good calculator for ejection charge sizing including shear pins. I usually double the result given for 'adequate' deployment. :p

IMO shear pins are the way to go for HPR. A solid rocket under boost and a good deployment is the result. Just drill a clearance hole for the pins and push 'em in. If they seem a little loose just twist the two sections in oppostition to one another and they're tight.

Give 'em a try - nothing to lose and you'll gain a couple of small holes in your airframe!

BHP
 

firemanup

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I've got shear pins and have used them in the past with the Thor.. just wasn't sure if that would get rid of the sloppiness or not, thought i'd ask before i drilled holes..

Seems that may be the way to go.. i'll get em setup and ready friday when i'm prepping stuff...

Thanks...
 

BHP

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I'd bet the shear pins will eliminate, or at least reduce, the sloppiness in the fit. That Estes V2 couples rather loosely and with the short shoulders of the nose and tailcones shear pins were necessary. I was quite surprised at how much the pins helped - it was then that I thought "Like a Rock" when I shook it and the name "Bob," as in Seger, came to be....
 

firemanup

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Ya comin over to NE with me this weekend pete...??
 

BHP

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Unfortunately, no. That's Nebraska Heat isn't it? Omaha's quite a drive for me, too. Four-and-a-half to five hours, I think, the last time I did it. And isn't the launch site further into NE than Omaha?

And I'll also miss the next Tripoli Southern Minnesota the following Saturday, too. Next launch for me is Tripoli Quad Cities the middle of JULY! Commercial on Saturday then some 'free' EX motors Sunday....

Hehehe - you gotta love this hobby - when you can get to a launch!
 

firemanup

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Yeh it's south of Lincoln actually... bout 4 hours for me one way....

I'll be making the TQC launch in July also. i don't remember which day though.. we need to get together again when we can launch some stuff...

If i'm lucky i'll have the BB II done by then we can drag that and your V2.... hmmmm wonder who'll win that one.... heh
 
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