Bridge Designs

[Less_Incidence]

My method for cutting basswood is to tape a straightedge to the table, tape the straightedge to the sheet of wood, and tape the sheet of wood to the table, then make lots and lots of passes along the straightedge with a razor blade (assuming we're talking about making strips from a sheet). X-Acto knives do a horrible job and aren't sharp enough. The razor blades you can get from The Home Depot in cheap packs of 100 that are marked "009 RD" are my tool of choice. There might be a better way, but I've never done it any different because this works like a charm.

[brayden box]

My coach and I tried to do that, but no matter how many times we tried, the strips were always off and warped.

[Less_Incidence]

What do you mean "off and warped"? There's no such thing as a perfectly flat sheet of wood, so they're always going to have some small amount of warp to them. I understand it can be hard to keep the blade vertical; when I was developing my wood stripping technique I used a very straight 1/2"x1/2" square piece of pine set on top of the sheet as a straightedge so that I could keep the razor blade pressed against the side of the wood block and keep the cut as vertical as possible. Now I have a steady enough hand to do it with only a straightedge (It's quicker that way as it's easier to apply a little more downward pressure), but that took time to develop.

[brayden box]

what kind of laser do you guys use?

[bernard]

what kind of laser do you guys use?

For laser cutting wood, the laser from a laser cutter. But it's not hand operated as that would be extremely unsafe. Some schools with nice donations or funding will have them. But given how successful many teams have been without it, laser cutting isn't necessary to do well in this event.

[brayden box]

Are different types of glue heavier than others?

[bernard]

Are different types of glue heavier than others?

Not sure about weights of glues, but I'm sure different glues vary in strength and the amount of contact/glue required for a joint that is strong. Cyanoacrylate (CA), often just called super glue, is very popular because it cures quickly and can be very rigid (depending on the type and amount of contact in a joint you're trying to glue, of course). Since I mentioned it, for joints, there isn't one joint that will work the best for everything, but typically some joints are stronger and others are weaker. End joints are an example of weaker joints. And for glues, there are different consistencies: thick, medium, thin. I'd guess medium is really popular. Thin is really runny and can add to the weight of your bridge easily if you're not careful since the glue can flow down the grain balsa easily, leaving not a lot at the joint.

[DoctaDave]

I believe duco cement is the lightest glue that is still practical for bridge building. It can be thinned with acetone and is still relatively strong and unlike CA glues, duco cement actually dries and loses mass over time where CA polymerizes and maintains the same mass in solid and liquid form. Duco does have its cons as it has a longer dry time and it requires "double gluing" to make strong bonds between wood. Also it isn't nearly as good at gap filling as CA.

Ultimately type of glue doesn't affect the structure weight that much. It is more important to work meticulously and perfect glue application techniques. For example my boomilever from a few seasons ago had over 100 joints and the glue total was about 0.2g which was less than 3% of the total weight. Even if I was able to somehow reconnect the hydrogen bonds between the cellulose of the pieces of wood and get no glue weight, my score wouldn't have changed by any significant amount.

[brayden box]

Then I need to put on less glue!!!

[samlan16]

Then I need to put on less glue!!!

I've heard of people getting insulin syringes, washing them out well, and loading them with CA to inject it neatly onto the balsa. Seems like it would solidify too quickly in the syringe, though...