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Strengthening fins

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Pippen

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I've got a kid with a fair project in the works that found out once it was all together that it needs some fin strengthening. He played around with just glue on both sides of some scrap balsa and that didn't seem to make it strong enough. He cut out balsa the shape of the fin and tried paper laminate and had trouble getting it smooth (is there some trick to that?).

Project check in is two weeks from tomorrow. What would you suggest, keeping in mind the short time frame and the fact that this kid always does a seriously perfectionist finishing job?

Thanks for any help...of course it wouldn't be fair project time without some problems along the way! I'll get some pictures up when I get a chance--the kids really outdid themselves in the creativity department this year...tigers, dragonflies, Thing-a-ma-jigs with mounted guns, something resembling a hatchet (oh my!).

Fins.jpg
 

troj

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When I've done paper laminates, I lay down a sheet of waxed paper, put down the fin (with paper on both sides), another layer of waxed paper, then put something heavy on top. This keeps it nice and flat while everything dries.

Another option is to spread thin CA over the fin's surface and spread it out with the edge of a piece of cardstock.

-Kevin
 
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BobH48

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I paper all of my fins with self stick label paper. I use Avery brand that I got at Staples but whatever brand you get, make sure that it's NOT the removable kind.

Make sure the surface is free of any sanding dust and burnish it down over the entire surface. I use the cap from a Sharpie as a burnishing tool just because it's handy.

Once the paper is on, run some CA along the edges of the fin to seal the paper except for the root edge. The root edge will get sealed when it's glued to the rocket and the fillets added.
 

Pippen

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Thanks for the suggestions.

If he were to do the label paper, could he still use Fill-N-Finish along the fin-BT joint or would the FNF make a mess of the paper?
 

mjennings

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Lisa,

Not to cause further headaches but the grain looks to be running parallel to the body tube.
 

Pippen

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Lisa,

Not to cause further headaches but the grain looks to be running parallel to the body tube.
The rockets aren't the headache this week...at least not yet. That would be the jams, jellies and marmalades. :p

He's got the grain running at about 30 degrees.
 

Intruder

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Since the fins are already attached, the easiest way to add strength would be to add some support struts. They would need to go from root to tip. It doesn't have to be perfectly vertical. 60-90 degrees from the fin grain should work. Making the struts look good; however, is going to be difficult. I've added a (very) crude sketch to illustrate what I'm talking about.

Untitled.jpg
 

BobH48

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Thanks for the suggestions.

If he were to do the label paper, could he still use Fill-N-Finish along the fin-BT joint or would the FNF make a mess of the paper?
Is he using Fill-N-Finish to make fillets?

I usually just make a glue fillet but I have used some F-N-F after the primer coat is on.

The label paper makes sanding sealer and filler unnecessary for the fins except maybe an edge here and there. That only leaves balsa nose cones and transitions to seal and fill.
 

Pippen

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Is he using Fill-N-Finish to make fillets?

I usually just make a glue fillet but I have used some F-N-F after the primer coat is on.
He usually does glue fillets followed by a little F-N-F to smooth out and give a little curved appearance. (He already had that done). He decided to go with the label paper--it took him a few hours and was a big pain with the fins already attached, but it definitely added strength. He used Titebond Molding & Trim Glue to add glue fillets along the joints to seal and depending on how that turns out will either use that or CA along the curved edges today.

He has one spot where the label paper is slightly dented at the crack and peel spot. Should that fill in with the primer?

Thanks a lot for the help--you can see the results below. Intruder, we have a rocket that's had fins broken off twice and those struts would be a perfect solution (the builder didn't want to laminate).

015.jpg
 

BobH48

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Looks like he did a good job with the label paper. It is definitely easier when the fins haven't been attached yet. Just make the label slightly larger than the fin and trim it after it's stuck.

I think the dent should fill in with primer. Don't put the primer on too heavy or you might get wrinkles. You don't have to mist it on by any means but don't saturate the paper.

Once the coat of primer is on, if you still see a dent, you can fill it with F-N-F if you want.

I use label paper on all my balsa fins now. It just saves all that filling and sanding work.
 

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