Woodworking/Building an Efficient Bridge.. Tips?
QUESTION: Hello! I am in this competition involving building a bridge that will hold the most weight. It is supposed to be a fairly small bridge. My teacher advised me to incorporate triangles in its design so it will distribute the force more easily. Do you have any tips regarding the design or any tips with gluing (I am using balsa wood). The goal is also to makee the bridge as lightweight as possible. Thank you!
ANSWER: Hi Katie, thanks for the question...yes triangulation is the key to the strength, and if you're allowed to use Google in your quest for knowledge, there will be a LOT of info for you to digest.
In my opinion, while design will be key, a good adhesive will make quite a bit of difference, and I would suggest a quick curing epoxy to glue up your bridge, and reinforce the gussets where triangulation points meet. That glue is System 3 - 2 part epoxy, and you can see it here:
and it can be found here, as well as other places:
It is a quick curing clear epoxy, that's very strong when dry and can be used to glue as well as reinforce angles and joints. It'll take a few minutes to get the hang of the viscosity, and abilities of this stuff, but it is one of the best, fastest and strongest curing, clear epoxies on the market. Easy to use, you just squeeze out equal parts onto a mixing surface,and thoroughly mix them together before applying. Little squares of cardboard and wooden coffee stirrers and toothpicks work great, as you'll go through quite a few of them, make sure to get your supplies ready before you start working. Mix in small batches only, because you will only have about 3-4 minutes working time once you stir the two parts together. You can glue up bridge sections on Wax paper,( I think the fully hardened epoxy will pull right away from the Wax paper, but experiment with this to make sure), laying flat, let cure, and then glue up the completed sections to form your structure, holding it together with Blue painters tape or similar. Then once your superstructure is complete, you can go back in and add drops of epoxy to the triangulated areas where sticks come together,( Blue tape on either sides of the intersections will help form a strong, neat joint), "gusseting" them together with even more strength.If you mix up some, then put a small lump on the very end of the stirrer, you can just hold it vertically over the area to be reinforced, and you can watch it slowly form a drop, that will slowly drip right off the stick, to precisely where you want it to drip. Patience and experimentation is the key with such an adhesive...but I have used this stuff for 25 years and swear by it for many, many jobs. Wear Nitrile, tight fitting gloves to start, as you'll want to keep the stuff off your skin, but once you get the hang of it, the gloves might not be needed using the coffee stirrers and/or toothpicks, as an applicator, and work in a ventilated area so fresh air is available. You might think this stuff is a little expensive, and compared to "just glue", it is...but it will easily put you in contention for the win, because it really is that much stronger, and space aged technology. And because it dries hard in about 5 minutes, it puts you at an advantage during the construction phase, as the glues most everyone else will be using will take a lot longer to dry between sessions...as always ...read and understand the directions and precautions of any product BEFORE using, to be safe and informed.
Hope that helps, and best of luck! Post back if need be, I'll be here for you.
---------- FOLLOW-UP ----------
QUESTION: I have a question concerning the general layout.
What type of triangles should be incorporated ? Should it have a steep curve, slope? Any other design tips? Thank you!
Hi again Katie, I'm sure that this is the part of the assignment that they want you to plan, design and execute. Simply asking someone else how to do it really defeats the purpose of the assignment. I already gave you a pretty big advantage in my opinion, by suggesting an adhesive that's so good, it's probably unfair...;-)
Five minutes of "Google" work on design for such a bridge will probably turn up thousand, or even hundreds of thousands of design ideas, and probably actual bridges that others have built. This assignment has been a staple of typical assignments like this for a lot of years...even when I was in school, and that was quite a while ago. I hope you understand that I, like your teacher, am trying to get you to use your brain, and not just rely on others and the internet. When I was young and got this assignment, there was NO internet, and we still managed to do pretty well with it, and come up with some very cool designs.....best of luck