Bridge Designs

[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...

[retired1]

The CA does not "set" all that fast in a syringe as there is little exposure to the air. You will go thru a lot of syringes over the build season. If you go this route, I suggest that you have a group of pieces ready to glue at the same time. Less syringes and less wasted glue.

I thought that we would have our teams try to use CA this year because of the speed and we went back to the double glue method as the CA joint would pull out a thin layer of balsa when stressed. The first coat of thinned Duco penetrates much deeper and ultimately provides a stronger joint. It sure takes a lot longer tho.

[JonB]

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...

Ask your biology teacher for micropipette tips and put them on your glue. Cheap, disposable.

[bernard]

Then I need to put on less glue!!! :lol:

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...

Ask your biology teacher for micropipette tips and put them on your glue. Cheap, disposable.

Or take a disposable pipette, stretch the tip with pliers and you'll have a narrower tip. Cut the pipette at a wider section, attach to the top of your glue nozzle.

[DoctaDave]

I've used 25 gauge syringe tips and they clogged too often with thin CA. I used a lighter to burn off excess CA but any pressure within the syringe would cause CA to shoot everywhere. The syringe also isn't very smooth and if the plunger is ever stuck a large amount of CA will be used. I think it is bad for applying tiny amounts of glue because of its inconsistency.

I ordered a 100 pack of thin tipped pipettes for about 10$ on amazon and they last a season and then some. I think they are actually easier to control than syringes and are a lot faster than the "piano wire" applicator.

[Less_Incidence]

Not sure if they're available anymore, but I have a couple of boxes of Zap brand "Flexi-Tips" which are silicone tip pieces designed to fit over the tops of CA bottles. They work well for applying CA or thinned Duco, and when combined with a small squeeze bottle, they're incredibly precise and easy to control, much more so than a syringe.