I kinda screwed up the fins...

Weldo said:

Regarding all the talk on papering fins, what's a recommended method? Just regular copy paper and wood glue? Or is there some special type of lightweight paper/glue?

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There are many methods (as you might guess). Normal copy paper and white glue (or wood glue) is quite common, works well and adds a lot of strength. Avery label paper (my preferred method, documented many times on this forum) also works well.

Where techniques vary are (a) how to trim the edges of the paper, and (b) how to seal the edges. I *always* sand off excess paper, and seal edges with TBII. Some folks trim the edges with a knife, and some (most?) folks seal the edges with CA. Some folks like to fold a single piece of paper of the leading edge of the fin; I always use one separate piece for each side. It all works. Best recommendation is to experiment with some scrap pieces of balsa and see what technique works best for you.

Thanks for the tip! I'll probably try the Avery paper on my next build.

Weldo said:

Regarding all the talk on papering fins, what's a recommended method? Just regular copy paper and wood glue? Or is there some special type of lightweight paper/glue?

Click to expand...

Regular printer paper (mine is marked as 75g/m^2) , thin layer of Titebond II applied to two (2) pieces of paper with a finger (important to paper both sides at the same time), then stick them to both sides of balsa fin.
Few useful hints:

• Paper both sides of balsa in the same go, else fin will warp.
• Apply wood glue to the paper, not balsa. This is the only way you can prep both sides simultaneously, plus glue doesn't soak into paper as much as it does into balsa.
• Once applied, put a weight on top of the papered fin, and let it dry fully. Put it under either a book, or a large cutting mat (I stick mine under 24x36" mat and continue onto the next fin).
• After glue dries, remove excess paper overhangs, and seal the fin edges with thin CA. Then sand and airfoil the fin to your liking.

I recently discovered that the weight of the paper is, almost, as heavy as the balsa fin material itself. Glue adds minimal weight.
Data for Screaming Eagle fins (I will post pics in another thread):

• Glued balsa fins: 2.7g
• Fins with two sheets of printer paper on top: 4.9g
• Finished papered fins after glue dries, CA-ed, sanded: 5.1g

So the lighter the paper you choose, the lighter the final papered fin will be!

HTH

Weldo said:

Regarding all the talk on papering fins, what's a recommended method? Just regular copy paper and wood glue? Or is there some special type of lightweight paper/glue?

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I have used 30 min epoxy with some good results. (If the fins are flat, with rounded leading/trailing edges.) cut the paper slightly smaller than the balsa so it covers only the flat part of the fin, square with the tip and root. Use a perfectly flat surface, tape down a piece of plastic bag. (Ziploc type) Use a single edge razor blade to squeege a very thin coat on the paper, place on fin, use another clean blade to squeege it down and get out bubbles. quickly prepare the paper for the other side, put the fin on the plastic bag material. after smoothing out the second side of the fin, place another piece of plastic bag on top of the fin and then weight it down with a flat piece of something on top then a heavy weight. (I used a full ammo can, about 20lbs.) Leave it alone for several hours...you can prep all the fins at once and weigh them all down at once. The bag plastic will not stick to epoxy. Wood glue sets up too fast, only good for very small fins. The epoxy will soak into the paper and the balsa.The end result surface is very smooth...

For strong fins for high power, I am getting away from all wood...Fiberglass or 3D-printed fins...(Make each fin with two halves, printed flat. Glue the halves together directly or sandwich with 0.030" G10 fiberglass. Super strong!

Weldo said:

Thanks for the tip! I'll probably try the Avery paper on my next build.

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Practice on scrap first!

afadeev said:

I recently discovered that the weight of the paper is, almost, as heavy as the balsa fin material itself.

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Can confirm: papering is not light. If I get some spare time at my bench I'll do a little weight comparison with CWF. I think someone may have done it before I don't remember where.

I created some custom "papered balsa" materials in OR so the extra weight would be accounted for. I think papered balsa ends up weighing as much or more than basswood, but of course basswood needs to be filled and finished as well (I have *not* had success with using only filler/primer for basswood).

neil_w said:

Practice on scrap first!

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Will do!

@beeblebrox I've been doing a similar thing on my fins lately but without the paper. I'll coat 'em in glue and press them in between a silicone sheet on a flat surface. It works pretty well for me, but adding paper would add even more strength.

My latest experiment was to press non-flat, air foiled fins. What I did was use some cloth rags between the silicone mat and the press boards to contour to the shape. So it layered up like, bottom board, two terry clothe rags, silicone mat, fins, silicone mat, two more terry rags, and then the top board. All this was clamped together mechanically.

Overall it was successful but the fins had a slightly lumpy surface texture. I think this is because the polyurethane glue I was using expands as it cures and the rags had a little give in them, even after clamps were applied. I might try something like a dense foam instead of rags next time. Like a kneeling pad or something.

I expect papering to work better.

You're probably right. Paper and glue will certainly be stronger than glue alone. With only glue you just get the tensile strength of the dried glue, which usually isn't much, but it's definitely better than nothing!

My sister has a bunch of Avery weatherproof labels from sticker making projects so I'll be trying that on the next build. That stuff sticks really well!

Weldo said:

My sister has a bunch of Avery weatherproof labels from sticker making projects so I'll be trying that on the next build. That stuff sticks really well!

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When I use label paper, I prep the wood as follows:
1) sand smooth with 400 and/or 800 grit sandpaper
2) brush off as much dust as possible with a soft paintbrush.
3) Use blue tape to remove as much additional dust as possible.

Then apply the labels. My theory is that removing absolutely as much of the surface dust as reasonably possible will maximize label adhesion.

Sounds good. Do you stick the blue tape to the balsa or just kind of use the sticky side to wipe it off? I was wondering if there's chance of the tape pulling out wood fibers.

Weldo said:

Sounds good. Do you stick the blue tape to the balsa or just kind of use the sticky side to wipe it off? I was wondering if there's chance of the tape pulling out wood fibers.

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I stick it to the wood and then peel off. Yes, it removes a few wood fibers, but I haven't seen any ill effects from that. The labels themselves are fairly stiff, and maintain a flat surface even if there are some pits underneath. In this respect they are different from using copy paper, which conforms much more to the underlying surface, especially when wetted by the glue.

Right on. Thanks!