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bending balsa stick

Old 03-24-2008, 09:16 PM
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Default bending balsa stick

HI....

I am wanting to bend a stick of balsa (3/8 by 1/4 in.) just a small curvature as part of the fuselage longeron, there is too much tension to curve it dry and then it snaps. I've heard about wetting balsa but am unsure of how much to wet?, for how long? etc

I would greatly appreciate some tips

Thanks

Old 03-24-2008, 09:28 PM
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Default RE: bending balsa stick

A lot of woodworkers steam wood to make it bend easier. You could also build up your piece out of thin strips. Just bend the lamination and hold it in place until the glue dries.
Old 03-24-2008, 09:48 PM
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Default RE: bending balsa stick

I've heard that a water/ammonia mix works well for making it flexible until it dries.. Not sure about the ratio, but you would soak the wood for a short period of time, pin it in place where you want to glue it and let it dry. When it is dry, it will retain the shape.
Old 03-24-2008, 09:55 PM
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Default RE: bending balsa stick

50/50 water and ammonia. It does not stain the wood and makes it very flexible while it is wet. It will still crack if you bend it too far, but it will bend a LOT more than if it were dry.
Old 03-24-2008, 10:39 PM
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Default RE: bending balsa stick

Yes indeed, a 50/50 mixture of water and ammonia. You can wet up all four sides of the stick and slowly bend it into the position that you want. You need to keep applying the mixture as you bend it. When you have it where you want it, pin it or tape it in place and let it all dry. Good Luck, Dave
Old 03-24-2008, 11:12 PM
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Default RE: bending balsa stick

What others have said.

I've soaked pieces of wood for several minutes in the sink in water only. Bent as needed under water... slowly if I need to work the material to the desired bend. Removed to pin in place to dry. Works well.

Not a stick but to give you an idea...

Soaked and bent and taped in place overnight...



After drying and removed from the plane...



Same can be done with your sticks.

Good luck!

somegeek
Old 03-25-2008, 12:57 AM
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Default RE: bending balsa stick

G'day Mate,
Forget the water, just use straight cloudy ammonia, from the cleaning section of your local super market, wet the wood using a small piece of rag, bend away.
Water will tend to make the balsa warp, as it dries, ammonia does not.
So don't mix water with the ammonia, & also, as soon as the ammonia hits the balsa, the smell disappears.
Old 03-25-2008, 05:40 AM
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Default RE: bending balsa stick

Water will not warp wood if the wood is held in place.

I've done a LOT of wood bending and I only use hot water.

Just wet the wood, let it soak in for a few minutes and put it in place.

Use ammonia if you want to, but it's not a necessity.
Old 03-25-2008, 08:04 AM
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Default RE: bending balsa stick

a trick that was passed down to me by a ship builder goes like this........get a piece of 1" PVC tube that is 4" longer than your strip, 2 end caps. cut a piece of 1/16" plastic into a disc that will fit inside the tube, drill a some 1/8" holes in it to allow breathing, then push it 3" inside the tube and glue it in place. on that same side, glue one of the caps in place to seal that end of the tube. now pour enough straight ammonia into the tube so that it is just below the disc with all the holes in it(easy to calculate by having an extra piece of tube 2.5" long). stand this up straight and place your strip into the tube and cap.................leave it in there for 24 hours..........at that point of time the strip will be like a drunken sailor and will conform to any shape you want provided you do not exceed the total bend allowable by the woods fiber.................never gets wet, doesn't swell like when soaked in water, and it will give you plenty of time to work the shape in before the ammonia gas effect wears off.............plus you can use CA right away.
Old 03-25-2008, 10:57 AM
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Default RE: bending balsa stick

Interesting - so the balsa simply absorbs the ammonia fumes using this technique?

somegeek
Old 03-25-2008, 11:40 AM
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Default RE: bending balsa stick

You can bend a sharp curve over a large soldering iron. Just be careful and quick.
Old 03-25-2008, 03:17 PM
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Default RE: bending balsa stick


ORIGINAL: somegeek

Interesting - so the balsa simply absorbs the ammonia fumes using this technique?

somegeek
ZACTLY!.......it's not the ammonia liquid that softens the wood..it's the gas.
this is an old model ship builders trick for planking.............turns any wood into a rubber band like consistency...............i'm a millman by trade and we use this for forming exoctics to build tight lams from.
Old 03-26-2008, 02:34 PM
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Default RE: bending balsa stick

Another method of getting a sharp curve in balsa is what woodworkers call kerfing. A number of sawcuts are made with a razor saw about halfway through the thickness until the wood will bend dry. Then when the curve is OK the sawcuts are filled with epoxy. This method is used in Peter Millers Turbulent plan and worked well for me.

However I would prefer to laminate from several thicknesses of balsa and maybe a thin 1/32 ply layer. Laminate over a simple former to make 2 similar longerons. Let the glue dry before building into model.

Beware! There have been several safety warnings about using ammonia.

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