As we all know, balsa wood is widely used in building models, such as plane models and bridge models. We should make sure the balsa we use could afford the weight before we use it to build a bridge model. The quality of glue we use should be proper to suit our requirements.
We should check the quality of the wood, the properties of the glue, and whether your pieces are straight and level. After that, choose the right type of balsa wood to meet our needs. The strength of the balsa relies on the weight of it. The heavier is stronger. If our subject has a weight limit, we will need to choose the balsa carefully. In order to insure the security of the subject and the satisfied weight, we need to use the heavy balsa and the light balsa together to complete our project. The light wood can be used to connect the parts of the bridge where are not bearing weight, on the contrary, the heavy wood can be used to subject the stress of compression. Sometimes, there are some damages inside the balsa wood which we couldn't find clearly, but we can identify potential vulnerable locations by checking each piece externally.
After selecting the suitable balsa wood, we need to choose the proper glue. Glues are divided by how fast it sets, whether it fills gaps well, and how strong a joint it creates. The CA glue are designed for small amounts and light wood. If we use heavier balsa wood, we need to use epoxy. Make sure every pieces of the balsa wood is straight and level before you glue them together. If not, the balsa bridge may collapse before you finish the framework. Ensure your cuts are straight with a tabletop miter saw, and use a a jig when you assemble the bridge to help make it level.