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Plastic Rivets, Cutting Kevlar, Airframe / Fin Repairs

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gsanders

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Hello, I have a couple of quick questions I am hoping someone can help me with...

(1) - I bought some large size (1/4" hole required) plastic rivets from GLR (Giant Leap). I drilled into the airframe and nosecone and inserted the plastic rivet. My question... just how hard do you have to push on those rivets to get them to insert into a "locked" position. I am a big boy with big fingers and I have given them quite a push but they have not begun to insert? What am I doing wrong? Should I get a hammer (just kidding)?

(2) - How do you keep the end of a Kevlar shockcord from fraying after you cut it to a desired length? With nylon you can apply heat but that obviously does not work so well with Kevlar.

(3) - One of my rockets (LOC Forte 3.1") had a hard landing in a rocky, plowed field and loosened two fins and put a little "pressure welt" in the lower airframe between two of the fins. I epoxied the fins back as best as I could but they need a little TLC and some beefing-up of the fillets. Is there some way to apply a thin, even coat of epoxy (or something better / more workable) to the lower airframe section (from just above the fins to the bottom of the airframe) so it strengthens that area so I can run a few "hotter" motors through this rocket without any worry of it self-destructing?

Thanks in advance...

Gary
 

Bat-mite

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Hello, I have a couple of quick questions I am hoping someone can help me with...

(1) - I bought some large size (1/4" hole required) plastic rivets from GLR (Giant Leap). I drilled into the airframe and nosecone and inserted the plastic rivet. My question... just how hard do you have to push on those rivets to get them to insert into a "locked" position. I am a big boy with big fingers and I have given them quite a push but they have not begun to insert? What am I doing wrong? Should I get a hammer (just kidding)?
Should push in with a thumb. I use dikes to remove mine, and throw them away after one use.

(2) - How do you keep the end of a Kevlar shockcord from fraying after you cut it to a desired length? With nylon you can apply heat but that obviously does not work so well with Kevlar.
Not my area of expertise.

(3) - One of my rockets (LOC Forte 3.1") had a hard landing in a rocky, plowed field and loosened two fins and put a little "pressure welt" in the lower airframe between two of the fins. I epoxied the fins back as best as I could but they need a little TLC and some beefing-up of the fillets. Is there some way to apply a thin, even coat of epoxy (or something better / more workable) to the lower airframe section (from just above the fins to the bottom of the airframe) so it strengthens that area so I can run a few "hotter" motors through this rocket without any worry of it self-destructing?

Thanks in advance...

Gary
Sounds like you want fiberglass cloth and laminating epoxy. Many experts here, hang in there for a bit.
 

timbucktoo

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(2) - How do you keep the end of a Kevlar shockcord from fraying after you cut it to a desired length? With nylon you can apply heat but that obviously does not work so well with Kevlar.
I wrap some masking or electrical tape around the end after I cut it & check it after every flight.
 

gsanders

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GLR says to pop them out (take rivet apart or remove it) with a screwdriver so they can be reused. Is this feasible, practical or even "do-able"?
 

Bat-mite

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GLR says to pop them out (take rivet apart or remove it) with a screwdriver so they can be reused. Is this feasible, practical or even "do-able"?
Yes, but the screwdriver can dig into your airframe. I used to reuse mine, but they warp after two or three uses. I decided to play it safe and go single use. Why damage a $200 rocket to save a 25c rivet?
 

Lowpuller

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I reuse mine all the time. I use a small screw driver and lots of care, easy to put in and out. Sounds to me like your hole is too small. Or the material your riveting together is too thick.

I always called lineman pliers dikes versus diagonal wire cutters.

ImageUploadedByRocketry Forum1491882835.654065.jpg
 

Steve Shannon

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A little epoxy on the end of the Kevlar strap will prevent unraveling.

I reuse rivets a few times; I use a knife blade to lift the head carefully. If the head breaks off just push the remnants of the shaft inward. I sometimes have had to use a tool or even a coin to set the rivet; when they are that tight the head usually breaks off when trying to remove them. When the hole is the right size and the rivet is the right length that's not a problem.

All the linemen I know call their lineman pliers "Kleins" because that's their favorite manufacturer of lineman pliers. [emoji1]


Steve Shannon
 
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Bat-mite

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The nickname "dike" is an acronym of DIagonal Cutting. DIC or "dike".
 

manixFan

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To 'expand' on the rivets, the small plastic fingers expand when you push the rivet into the base, so the fingers of the rivet have to extend past the two pieces being joined. If the rivet is too short, the fingers can't expand so the head will be very hard to push in. If you look at the rivet base, you can see the shaft of the rivet above the fingers. The thickness of the material you are holding together should be about that or just a little deeper. The best solution is to get longer rivets. For an especially thick airframe I have I needed to get 10mm rivets that would work for a panel thickness of 3.5-4.5 mm:

https://www.amazon.com/gp/product/B008MP1LH6/?tag=skimlinks_replacement-20

I only use the rivets once. I use a very sharp knife blade or Exacto to pry the rivet up a bit and then pull it out. It's too much work to try and keep track of all the little bits so I just toss them as I remove them. The link above shows 100 rivets for less than $10 so cost is minimal. Plus there is the chance the shaft may get damaged when removed.

As to Kevlar, I wrap the ends with tape - I find that just plain masking tape works fine. I've also used a drop of CA or Epoxy but I didn't like how it made the end hard. I used to whip the ends with Kevlar thread but that got old although it looked cool.

Good luck,


Tony
 
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gsanders

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These plastic rivets from GLR are certainly big enough I think. I have included an attachment of a screen-shot from the GLR webpage for this item showing dimensions.

Rivets.jpg

I mean these plastic rivets are just plain tough to push in, even without inserting them through anything. They are being used on a factory airframe and nosecone from a LOC Big Nuke (5.54" diameter). I have drilled a .25" hole for insertion as/per the instructions of GLR.
 

Bat-mite

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The combined thickness of your tubes needs to be about half of dimension C in your pic. If that is clear, they shouldn't be that hard to push in. Call Kent.
 

gsanders

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I should be good on thickness I believe. I just e-mailed GLR to get their opinion on why the plunger is so hard to insert into the rivet body, even just holding it in your hand (not inserted into anything)?
 

soopirV

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I tried using the rivets that came with a Madcow kit, and just couldn't develop a feel for them. I instead epoxied in small squares of G10, drilled 2 or 3 holes through the airframe, avbay coupler and fiberglass, and tapped for 6-32 (maybe #8...don't remember). I've taken this approach with all my rockets now, and just have to tighten a couple of pan-head machine screws.
Agree with the others on the kevlar cord- a dab of epoxy is plenty to keep it from fraying, and also with the use of Fiberglass cloth to help repair a ding in an airframe. My L1 bird took a smack from the nosecone at some point, which stove a gash in the lower airframe. I popped it out as best as I could, and just wetted out a 4 or 6oz piece of glass over the area with some 3:1 US Composites laminating epoxy (not an expert by any means, but it has served me well when I glass a tube). It's not perfect, but it's strong! With time and energy, i'm sure I could've made it an invisible repair, but I was busy working on my L2 :)
 

sharkbait

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1. Rivet head should insert easily when free. Should only take minimal pressure to insert when joining. Can't speak for the GRL rivets, but I have gotten some bad rivets from McMaster-Carr before.

2. Heat shrink tubing makes a nice clean finished end on Kevlar and all other types of harness material

3. Tip to Tip glassing will strengthen your fin can to survive high G flight profiles, but if you have a light weight cardboard airframe and don't glass it also then the airframe can easily become your failure point
 

KenRico

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I learned from CJ that if i put some green masking tape around the kevlar and then cut it in the middle of the tape ..i dont get the fraying and unraveling.

Kenny
 

dhbarr

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I learned from CJ that if i put some green masking tape around the kevlar and then cut it in the middle of the tape ..i dont get the fraying and unraveling.

Kenny
Wish vendors would ship it this way :-/
 

gsanders

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RE: Fin area / Lower airframe repairs?

What about buying another body tube (either standard phenolic or even FG) the same diameter as the original and then cut out the full sections of this new body tube to fit between the fins (less the fin mount area). Then epoxy these pieces over the existing lower airframe (between the fin areas). Then smooth things up with a little RocketPoxy near the fin area and the top and bottom of the newly epoxied-down body tube sections? A person is essentially double-walling the lower body tube area (between the fins). Too heavy? Too ugly?
 

redleder

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I use a drop of CA on the Kevlar and then cut it normally.


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Onebadhawk

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To stop Kevlar from fraying--
A snug wrap of high tack masking tape on the Kevlar before you cut it..
Then cut it in the center of the tape..
Then a drop of thin CA will wick right into the cut end and it wont fray at all anymore...

Teddy
 
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