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CA soak fins: How, where, why?

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Joshua F Thomas

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I did a forum search on this but didn't find what I was looking for. I've seen references to using CA to make fins stronger. I've got a scratch build with 3/8" balsa fins that need some extra strength.

So questions be:

1) Which CA? I've got 5-minute thin and 30-minute gap filling.

2) Where? Edges, or the entire surfaces, or what?

3) What is this actually doing? Does the CA bond the internal structure together?

Also, CA exposed to air usually leaves a 'frosting'. Do you then sand that away?

Thanks in advance.
 

rklapp

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I've seen people use thin CA on the edges but seems really messy and a PITA to work with. I've spilled some on my nitrile glove and it started burning and melting the glove. I also spilled a bunch on my brand new bench because it ran along the side of the rocket. What a mess...

Lately, I use Avery labels for large fins and thinned wood filler for smaller. For edges, I use wood glue to fill the holes.
 

Steven

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I cut patterns from tracing paper 1/8" oversize or so then use thin CA on top. Immediately after application I wipe the surface down with a paper towel. I saturate things well. When dry, I start to sand with 320 and finish up with 400-600. It strengthens the fins and seals the wood at the same time. No grain.
 

kuririn

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1) Which CA? I've got 5-minute thin and 30-minute gap filling.
You want thin CA. There is thin, medium, and thick CA.
Haven't heard of 5 min and 30 min CA. Isn't that epoxy?
2) Where? Edges, or the entire surfaces, or what?
Entire surface. First coat will rapidly be absorbed by the wood. Subsequent coats will stay on the surface as the wood becomes saturated. Wip off the excess. Be careful, thin CA has a habit of running all over the place. Use a micro applicator and do small sections at a time.
3) What is this actually doing? Does the CA bond the internal structure together?
The wood fibers soak up the CA and becomes hardened when it cures.
Also, CA exposed to air usually leaves a 'frosting'. Do you then sand that away?
The CA soaked balsa will have a rough texture, so it needs to be sanded smooth.
I like to paint the tips of long pointy nose cones with thin CA to lessen the chances of them breaking off. Not the whole cone, maybe the first two inches or so. Also the lips of body tubes to prevent zippering.

Probably not in wider use cuz of the cost factor.
 

Joshua F Thomas

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You want thin CA. There is thin, medium, and thick CA.
Haven't heard of 5 min and 30 min CA. Isn't that epoxy?
My bad, that should have been 5 seconds. The thick gap filler stuff says "30 minutes to full cure".


Entire surface. First coat will rapidly be absorbed by the wood. Subsequent coats will stay on the surface as the wood becomes saturated. Wip off the excess. Be careful, thin CA has a habit of running all over the place. Use a micro applicator and do small sections at a time.
How do I wipe it off when CA causes two things to stick together very rapidly? What are you using to wipe off the excess?
 

kuririn

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When you see that the liquid is no longer being absorbed and is just lying on top of the surface then additional coats will be superfluous. You can also drip off any excess instead of squegeeing it off. And any excess lying on the fin surface after drying can be easily sanded off. What I like to do is do a small section. When that becomes saturated move the excess to the next section and let it soak in. Careful, thin CA is even runnier than water. I once glued two stages of a rocket together when the CA wicked into the stage coupler joint.
Forgot to mention, glue and fillet the fins with wood glue before painting with CA. That way the wood glue will soak into the fin joint and your bond will be strong. If you do it the other way the CA will have soaked into the balsa and the wood glue will not have as strong a bond with the balsa.
 

Joshua F Thomas

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When you see that the liquid is no longer being absorbed and is just lying on top of the surface then additional coats will be superfluous. You can also drip off any excess instead of squegeeing it off. And any excess lying on the fin surface after drying can be easily sanded off. What I like to do is do a small section. When that becomes saturated move the excess to the next section and let it soak in. Careful, thin CA is even runnier than water. I once glued two stages of a rocket together when the CA wicked into the stage coupler joint.
Forgot to mention, glue and fillet the fins with wood glue before painting with CA. That way the wood glue will soak into the fin joint and your bond will be strong. If you do it the other way the CA will have soaked into the balsa and the wood glue will not have as strong a bond with the balsa.
Hm, I was going to do this *before* trying to install the fins, as I usually fins that less of a hassle. I suppose I can CA the non-bonding areas.
 

kuririn

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I find that thin CA has a way of migrating beyond the area you are working on..
 

Joshua F Thomas

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When in doubt: Practice.

I used some extra balsa sheeting I had to try this method. I ended up being able to both soak the surface in CA *and* using a second layer of CA to paper the balsa. It's silly strong now, feels more like plywood than balsa. 10/10 would do again.
 

heada

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You can also use Deft Sanding Sealer. 100% NC lacquer based. It'll soak in and cure hard similar to thin CA but not insta-glue your fingers together.
 

rklapp

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Have you tried it? Yes, how many coats did you use on fins to seal grains?
I ordered. The advantage is that this comes in a manageable quantity. I’ve heard to put on one thick coat then two thin coats.
 

afadeev

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2) Where? Edges, or the entire surfaces, or what?
3) What is this actually doing? Does the CA bond the internal structure together?
You can go CA-ing either just the edges, or the entire surface of the fin. The choice depends on what affect you are trying to achieve:
  1. Seal the surface of the balsa fin for smooth paint-ready finish.
  2. Structurally stiffen and strengthen the wood surfaces, plus #1.
  3. Seal the edges of balsa/plywood fins from delaminating and/or pitting.
Super-thin CA is great at penetrating the pores in wood and paper. That seals pores shut, smothes the exterior surfaces, and stiffens the part. The downsides are that it makes the fins a bit more brittle, and also removes the possibility of gluing the fins to the airframe with PVA/TiteBond type glues. You have to use CA or Epoxy to glue the fins after CA-ing them (not the end of the world), but may not be what you want.

In the context of the fins, for #1 or #2, sealing the entire surface of a large fin takes work, requires more CA, and will lead to a LOT more sanding.
CA doesn't spread evenly, and cheaper CA brands generate tons of irritating smoke. Thus you either have to spray CA onto the fins outdoors, or pay 3x (triple) the price for Super Gold CA: http://www.erockets.biz/search.php?Search=&search_query=ca

If strength (#2) is your primary goal, and a little extra weight is OK, the optimal outcome will be achieved by first papering the fin (search for threads on that), then either CA-ing the papered surface, or just the edges.
For example, when you want to make sure that your Screaming Eagle wings will never chip or break:
papered fin, primered.jpg

If you need strength (#2), but can't afford extra weight, like in the case of helicopter blades, then you only fill the grains (with primer, or wood filler), and CA on top:
heli-roc.jpg

Do I need to do multiple coats, or just one pass all over?
If you can manage to apply CA in one pass - well done!
For me, it usually takes multiple spray passes across the surface of the fin, then filling in more rough patches where the CA had been absorbed by the wood more than in the nearby areas.
Then you sand.
CA is hard, but it can be sanded. Just takes time, and patience.

There's also this for sealing the fins (and edges) without warping the balsa but I hear it smells nasty.
Have you tried it? Yes, how many coats did you use on fins to seal grains?
That looks similar to the Elmer's wood filler.
A few layers of application, followed by sanding, will definitely fill the wood grain in the fins, and add some strength. Not as much as CA would, but some.

The trouble with all water-soluble fillers (like eRocket's or Elmer's), is that water has a nasty tendency to warp balsa, basswood, and plywood.
For that reason, I avoid them on fins (but do use them on airframes):
fillers.jpg

HTH,
a
 
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rklapp

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That looks similar to the Elmer's wood filler.
A few layers of application, followed by sanding, will definitely fill the wood grain in the fins, and add some strength. Not as much as CA would, but some.
The trouble with all water-soluble fillers (like eRocket's or Elmer's), is that water has a nasty tendency to warp balsa, basswood, and plywood.
For that reason, I avoid them on fins (but do use them on airframes):
I rewatched the eRockets presentation and he said it's water based. The eRockets website says don't breath in the vapors, we'll see if it's different than wood filler.
 

Joshua F Thomas

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I used a CA soak *and* papering on my scratch-build fins. They came out nice. Have to use more CA than you expect, it spreads very thin very rapidly.

trixie_ttw_fins.jpg
 

BABAR

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I used a CA soak *and* papering on my scratch-build fins. They came out nice. Have to use more CA than you expect, it spreads very thin very rapidly.

View attachment 427344
That’s one I haven’t seen before (of course, there’s lots of stuff I haven’t seen before,)

So do you cut the paper to fit, lay it on the fin, and then soak through from the outside with thin CA, or so you apply it some other way?

I’d be curious for anyone with experience comparing CA papering with white glue or wood glue papering...... feel free to chime in.
 

kuririn

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I've always done one or the other - not both at the same time.
 

heada

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I do a version of"both" for mid power rockets to emulate fiberglass tip to tip.

I use 70lbs Kraft paper cut slightly oversized to cover the fins and body tube between. I the get out my fireworks pasting setup which is a plastic cutting board, pre-mixed wallpaper paste (Roman PRO-543 I think) and a disposable chip brush.

- Put a dollop of paste on the board and spread it out.
- place one of the pieces of paper on the paste and brush it out with paste until saturated.
- flip it and repeat. Paper should be saturated on both sides.
- crumple up into a ball and set aside and move to the next one. This is called breaking the grain and it helps lay it flat later.
- after all paper sections are done, lightly paste where they'll go on the rocket.
- take one of the balled up papers and unball it and lay it flat on the board and recoat with a light amount of paste, both sides.
- apply paper to rocket like you would tip to tip making sure to get fin to tube fillet area well.
- smooth out the paper with a finger to ensure its flat with no air pockets
- repeat for all pieces of paper
- set aside to dry. Takes about 24 hours and will set up rock hard.
- once dry, trim the overhang with an x-acto.
- CA the paper with thin CA
-sand from 220 up to 400 for a smooth, no grain finish

I had a 90 pound dog step on a surface mount fin like this and the body tube kinked but the fins didn't budge. Much stronger than any other setup I've done except fiberglass tip to tip but 1/4 of the weight of glass and epoxy.
 

Joshua F Thomas

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I first soaked both sides in CA, using the ”squeege” method to remove excess. After drying, I sanded away excess CA until smooth

I cut paper to size and did a test fit. I then applied more CA, removed excess, applied paper and compressed hard, center outward to prevent bubbles.

Some of my fins are better than others, as the temptation is to not overuse CA. If you underuse it, you will get paper bubbles. I has to fix a few by cutting tiny holes and using a long CA applicator.

Practice a few times before trying on actual fins.
 

jrap330

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So you punch a hole in the paper bubble and inject some additional CA via a long applicator? Well, you can not tell from the photos. Looks perfect. Any issues hen you applied the paper and had to correct the placement/orientation or does CA give you some time before finally gluing the paper?
 

Joshua F Thomas

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I admit those are the better looking sides. One of the other fin sides need a bunch of extra work and I will probally end up CWFing over it in order to get a clean enough surface for paint. My technique could use some practice.

The CA gives virtually no time when you apply it. Practice where you want the paper several times before putting it down, or make the excess sides very, very generous so you don't miss any of it. You can do each side one at a time which makes cutting the excess much easier.
 

neil_w

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That is an interesting process. I have to wonder, though, if it's really any better than just papering normally and then applying CA?
 

jqavins

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I did a forum search on this but didn't find what I was looking for. I've seen references to using CA to make fins stronger. I've got a scratch build with 3/8" balsa fins that need some extra strength.
Wow, 3/8" balsa? What's this rocket look like? I can't think when I'd want thicker than 1/8" or maybe 3/16" before switching over to basswood or plywood.

Lately, I use Avery labels for large fins...
This is second hand knowledge, but everything I've read states that papering with label paper is great for making finishing easier, but it doesn't add any strength to speak of.

I'm usually not concerned with keeping weight down to the lowest I possibly can, so if I ever feel like I need more strength than papering with white or wood glue will give me then I just use stronger wood.
 

rklapp

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I'm usually not concerned with keeping weight down to the lowest I possibly can, so if I ever feel like I need more strength than papering with white or wood glue will give me then I just use stronger wood.
The general consensus is to add thin CA to the adhered paper. I haven't tried it yet. I might start applying the CA the edges. I rarely crack a fin but I only fly LPR. Mostly, I break the fin off when it pulls the epoxy off the paper tube, usually when the parachute fails.
 
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