In this instructable: I will show you how to bend balsa wood.
This technique is mostly used to build scale model airplanes where they often bend balsa wood. To make everything easier to understand, I made a scale model of the Butterfly chair, by Arne Jacobsen. This chair, which you can see in the picture above, mainly consists of bended wood.
Step 1: Options to Bend Balsa
Before we take off, it might be important to inform you that
there are 2 ways of bending balsa wood. The first way is by using a steam gun. The second way is by using ammoniac and hot water.
I used the second way because I hadn’t a steam gun. This technique is very easy, but dangerous because you work with pure ammonia. Ammonia is a toxic material that corrodes the eyes, so always wear safety gear, most importantly safety glasses to protect your eyes!!! I could fix it at my school, but if can’t get it, you can always use cleaning products based on amonia, like cilit bang.
The proportions are 1/3 ammonia and 2/3 hot boiling water. The longer you put your balsa wood in the liquid, the easier it is to bend.
Step 2: Materials
First of all, make sure you have all your tools and material with you before you start. In the pictures above, you can find everything I used to bend the balsa wood in a clean way.
Step 3: Drawings
So now I start with my drawings. Out of a simple front, side and top view I made a template. I copied the outline of my template on the wood.
I could have done the same in CAD and lasercut the shape, but it was easier the old fashion way.
Step 4: Prepare Wood
First I cut out my shape a little bit too big with the scroll saw. Be careful for blow out. Try to have a zero-tolerance plate under your piece.
Afterwards you can bring the shape closer to the line. The outer curves with the disk sander and the inner curves with the spindle sander. You need to think about the positioning of your piece in relation to the fibre-direction. The big radiuses following the grain so it’s less likely to split. The small radiuses perpendicular to the grain direction.
Step 5: First Soak
I’m soaking the wood in the ammonia mix/liquid for about 10 minutes. The time depends on the thickness and the density of the wood. The proportions are 1/3 ammonia and 2/3 hot boiling water. The longer you put your balsa wood in the liquid, the easier it is to bend.
To give you an idea. My piece had a thickness of 2 mm and after 10 min it was ok.
Step 6: First Bend
I made a template in a rigid material. It has a smaller radius then the final model cause the wood will come back a little bit to its original shape.
I fixed the wet balsa wood on the template with elastics. To prevent an imprint in the balsa wood, I put a plastic sheet between the balsa wood and the elastics. I cut some holes around the shape so it would dry better.
Step 7: Second Soak
Use the same steps as the first soak.
Step 8: Second Bend
The inside corner of the small radius can cause some problems. The fibers can't compress enough and the wood is buckling. The outside fibres can stretch pretty good. A better technique may be laminating sheets of veneer directly in the bend.
I fixed the balsa wood with clothespins and elastics as you can see in the picture above.
Step 9: Finishing Touch
I used some grinding paper to give it a good look.
You can see what grid to use in the table above. I need to be gentle cause balsa is really soft.