Building a model bridge is one of the most rewarding hobbies I have done in my entire life . I have learned a ton about working with wood and tools. I have also learned the basics in bridge engineering, and have a greater appreciation for real bridges. Model bridge building has also given me a originative outlet that I can share with others. Not only does it give me something fun to do, I can show off my creations and prove their abilities.
To start out building a model bridge, you have to decide what materials to use. Frequently I use Balsa or Basswood. These two woods are common, and you can find them in most any hobby store. You can also use popsicle sticks, toothpicks, paper, cardboard, and tons of other things. Often I choose to make a balsa wood bridge because they are versatile and fun to construct. What materials you choose will depend on the goal you have for your bridge.
Most competitions tell you what materials you can use, and limit your choice. If you want to build this model bridge to exhibit on your shelf, then you can use materials that have more aesthetic appeal. However, if you are building a bridge to test it to failure, in order to see how much weight it will hold, then you want to use efficient materials.
Once you decide what materials to use, you need to start designing your bridge. Decide how long you want the bridge to be. Are you trying to set the world record for the longest popsicle stick bridge, or are you going for an easy project? You also need to pick out a truss design for your bridge. There are three standard trusses used in engineering, the Warren, Pratt, and Howe. After you pick a design, I find it helpful to draw it to scale on graph paper.
After you have designed your bridge, you need to start construction. Make sure you have all the tools and materials you will need, such as glue, saws or exacto knives, clamps, jigs, wax paper, and such. The glue you choose is important to the strength of your bridge. I recommend Cyanoacrylate Glue. Use your drawing on graph paper as blueprints to build your bridge on. Consider covering your blueprints with wax paper to help keep glue from ruining your drawing. You can do this step in two parts. Make one side of the bridge first, and then remove it from your blueprint. Repeat for the other side, and then join the two sides together to make a bridge.
Now that you have finished your bridge, you can enjoy it. If you are going to test it, remember to wear safety goggles. If you are going to display the bridge, or use it for a model train set, you are good to go.