Bending balsa.

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Senior Space Cadet

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I'm wondering if this is a lost skill. Maybe everyone knows about it, but in case you don't, here it is.
When I was young, I was obsessed with anything that flew, especially anything that soared.
I was always making gliders out of balsa.
Back then, there were books on balsa construction.
One of the tricks was bending sheet balsa. The thinner, the easier.
You'd draw straight line where you wanted to bend the balsa.
You'd run hot water, from the faucet, along that line. Probably both sides.
Then using a hot clothing iron, you'd press the edge of the iron along that line (moving the iron forward and back) while applying an upward bending force to the other side. Doing a little on each side of the line.
The balsa will take a permanent bend.
Probably not as useful in Rocket building, but if you want to make flaps for your fins or something, this is much stronger than trying to glue two edges together. Probably more aerodynamic too.
Hope this helps someone.
 

Antares JS

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Not an entirely lost art - this kit uses it to airfoil the rotor blades.

 

Zeus-cat

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the technique is used in wooden ship models to make the hull.
 

kuririn

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Not an entirely lost art - this kit uses it to airfoil the rotor blades.
Yep, see the first few posts in my build thread for pics of bending the rotors with an ammonia/water solution.
 

BABAR

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Here’s a post from a guy @Rktman who built and successfully flew the RingHawk, so he obviously figured it out

 

SecondRow

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I think the Fliskits Mira has you bend balsa for the fins using hot water.
 

Funkworks

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the technique is used in wooden ship models to make the hull.
Just just models I think. Before metals became standard, ship hulls were wooden, and curved. Bending and curving wood with water is the real deal.
 

Funkworks

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Bringing this back up.

I'm very intrigued by wood bending techniques, so I'm about to try curving a piece of balsa around a rocket tube. This would mostly be for aesthetics reasons related to a wood-looking rocket. Think about it: wrapping a thin balsa sheet around a tube could be part of a killer steampunk design.

Anyway, if anyone has links or documentation discussing bending or curving balsa, I'll be collecting them.
🧲🧺🚚📮📭📥
 

neil_w

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I'm very intrigued by wood bending techniques, so I'm about to try curving a piece of balsa around a rocket tube. This would mostly be for aesthetics reasons related to a wood-looking rocket. Think about it: wrapping a thin balsa sheet around a tube could be part of a killer steampunk design.
On my IRIS-T I bent 1/32" balsa right around a BT55 (with the grain, of course), no problem, no special techniques. Just need to keep it wrapped tightly while the glue dries.

 

Funkworks

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Ok well that sounds easy enough. I'm stumped. Can't wait to try!
 

dr wogz

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Funkworks

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I thought of veneer but will probably stick to balsa because I still have about $28 worth of stain to use up. Plus it’s always lighter, it’s available in many dimensions, and sticking to one kind of wood will make it easier to color-match with other parts.
 

Senior Space Cadet

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I have a book on bending wood. Normally a steam box is used for things like oak. I'm thinking you would probably want to soak the balsa in hot water and keep steady pressure on it till it bends around your form (rubber bands?) Might have to do it in stages.
I made bended laminations for my boat. I took strips of 1/4 inch plywood, coated both sides with epoxy, suspended the ends, hung a heavy weight in the middle, then put clamps every six inches. Laminations are good for making thicker bends.
 

Funkworks

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I have a 1/32" balsa board in my wood stock and tried curving it yesterday, both ways.

Without water, i can curve the board to have maybe a 1-4 feet radius, on an imaginary end-to-end full circle, which is remarkable.

But curving it the other way, side edge to side edge, I can actually make a full circle with less than a 1-inch radius. Who’d a thunk. Really amazing.

I’m a little disappointed that I won’t need water or get to learn a new specialized technique, but glad that for my current projet, the solution is so easy.
 
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neil_w

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keep steady pressure on it till it bends around your form (rubber bands?)
Rubber bands will tend to cut into the balsa and leave indentations. Clamping the wood in place without messing it up can be tricky. Need something that will apply even pressure.
 

Rktman

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Rubber bands will tend to cut into the balsa and leave indentations. Clamping the wood in place without messing it up can be tricky. Need something that will apply even pressure.
Ace elastic bandages. Unsurpassed. And they wick away moisture so your balsa can dry in a reasonable amount of time. Also thumbs up on straight ammonia, or Windex with ammonia.
 

neil_w

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Ace elastic bandages. Unsurpassed. And they wick away moisture so your balsa can dry in a reasonable amount of time. Also thumbs up on straight ammonia, or Windex with ammonia.
Excellent. Noted for the future.
 

Funkworks

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I get the elastics, but you guys lost with the Windex and ammonia. 🤔
 

Rktman

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I get the elastics, but you guys lost with the Windex and ammonia. 🤔
Ammonia softens the lignin in the balsa (the stuff that gives rigidity to wood). Once softened you can bend/stretch the balsa perpendicular to the grain (across the width of the balsa sheet). Form it around a mandrel like a pvc pipe or other shape and bind it tightly with elastic bandages, tape, strips of cloth, etc. and let it dry thoroughly. It'll keep its new shape once the ammonia evaporates and the balsa is dry.
 

neil_w

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Windex is a way to apply a very small amount of ammonia. I usually use it when bending.

Stronger ammonia can really soften up wood tremendously. I have *not* tried it, because I don't feel like dealing with strong ammonia in my house.
 

Rktman

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Windex is a way to apply a very small amount of ammonia. I usually use it when bending.

Stronger ammonia can really soften up wood tremendously. I have *not* tried it, because I don't feel like dealing with strong ammonia in my house.
Try living with a cat. The ammonia fumes mixed with other, um, aromas from a cat box 🤢 makes Windex or a bottle of ammonia far more tolerable.
 
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Funkworks

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I won't need ammonia or Windex this time, but hopefully in a future project.
 
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