Building a tower using balsa wood can be a challenge for even experienced modelers. It's an experiment in engineering and construction that can mastered only through trial and error to see what works best. But there are a few tips from choosing the wood to creating the joints that can give you a head start on building strong towers that can take a heavy load using an extremely light material like balsa.
Choosing the Wood
Not all wood is created equal, and choosing the right balsa for your tower is important to increasing the strength of your tower. Examine each piece of wood closely before choosing it for your tower. A strong piece of balsa wood to use comes from a dense stick. Check the denseness of your stick by doing a squeeze test. Lightly squeeze the stick between your fingers; the more resistant it is to crushing when squeezed, the more density to your balsa stick. This will damage less dense sticks, so it's best not to squeeze before purchase. To determine strength without the squeeze test, look at the wood color. The darker the wood, the more dense it is likely to be.
An important but often overlooked part of a balsa wood tower is the glue used to hold the pieces together. Choose glue that's low in weight, quick drying and strong. A good choice for balsa towers is yellow wood glue that you've thinned slightly with water. The formula is 70% glue to 30% water. Mixing the glue will lower the weight of the glue and help it to seep into the wood's surface, strengthening the joint. Take care not to get the oils from your hands onto the joints to be glued, as this oil will interfere with the strength of the bonds.
How you assemble your tower is the greatest determinant of its strength. When joining two wood pieces, make sure there are no gaps. Sand the wood flat if necessary to provide an even, level joint, as glue makes bad filler material. Use lap joints whenever possible, with one piece overlapping the other. Balsa wood isn't very strong and tends to tear easily at the face of the joints, but with your thinned glue soaking into the surface this should not be a problem.
If a lap joint isn't possible at the intersection and you have to use an end joint where one wood piece is joined at the end of the piece with the surface of another, create a gusset at the connection for added strength. A gusset is a small piece of wood which overlaps the two connected woods at the joint and adds the strength of a lap joint where an end joint has been used. By placing a gusset on both sides of an end joint you can create an even stronger joining.
Use x-bracing when building your tower. X-bracing requires that the struts in the length of your tower always cross one another in order to distribute the load weight on your tower. This should help you build your tower higher and provide strength at every brace level.