Elevated Bridge B/C

[geraldatwork]

I think the fact that CA glue bonds almost instantly which allows the builder to build much faster "out weights" any other glue.

[sr243]

I have built numerous bridges out of both wood glue and CA. Guess I'm the only person to support wood glue. Although it is heavy, I have found the glue to be very useful for shear and tension. I have mixed it with weldbond and water in order to get it lighter. The weight is somewhat significant, about 0.5g as oppose to .25g by CA but to me it isn't enough to switch to CA. With CA i found constant problems with the glue. I find out sometimes i put glue and it stays but is not fully connected and just partially connected but since it is strong, it will stay for a while. When it comes to testing, i found it that it breaks there because of the glue. Wood glue expands so if there is a gap it will fill it while CA will seal the wood. Don't get me wrong, I have built very good CA towers and bridges. However wood glue has a more consistent and higher average ratio.

what do you mean by "partially connected" that's why your suppose to put light pressure on the two pieces your gluing, so when it dries it'll dry attached together.

What i mean was when it was dry, sometimes it is attached but when you put slightly more pressure on it, it breaks. I really hate it when i move it and it doesn't come off and when i test the bridge, it breaks there from a joint failure.

[rman]

Virtually all the normal glues available have densities that are about 1, so there is little difference in "weight" from one glue to another. The main reasons for one glue to weigh more than another after drying or curing, is how much you use and how much of the glue evaporates. Sigment and Ambroid lose a bunch of weight while drying, while superglue, epoxy, and polyurethanes lose no weight (I actually think that polyurethanes gain a bit of weight because they use moisture in the air to cure). The biggest factor though, is using the minimum amount of glue possible. We used to actually measure the glue into a container so that we could see how much we were using. If we saw that we were using more then a few tenths of a cc then we knew the bridge would be too heavy.

The main reason for using CA (superglue) is that it is very strong and cures extremely fast. If you have a bridge with 50 joints (or more) and you have to wait several hours for each joint to cure or dry (as with polyurethane or wood glue) it will take a week or more to build a single bridge. Most of the very competitive builder build many many bridges before they settle upon a particular design and construction technique.

I have seen extremely competitve bridges that used several different glues in the same bridge. The type of glue depended on how stressed the joint was, how large the joint was, how difficult it would be to hold the joint together while it was drying or curing, etc.

[hbk.showstopper]

I think the fact that CA glue bonds almost instantly which allows the builder to build much faster "out weights" any other glue.

there's more than one type of CA glue because I did an experiment where I made several bridges but they were made with different versions of the glue like liquid or gel and it did make difference like some parts of the bridge were more sturdy than others so I guess it also depends on what version/type of CA you use...

[smartkid222]

I think the fact that CA glue bonds almost instantly which allows the builder to build much faster "out weights" any other glue.

there's more than one type of CA glue because I did an experiment where I made several bridges but they were made with different versions of the glue like liquid or gel and it did make difference like some parts of the bridge were more sturdy than others so I guess it also depends on what version/type of CA you use...

and what did your results show?

[hbk.showstopper]

wel the gel is better at bonding but if you're reinforcing then the liquid kind is better.....

[andrewwski]

The gel types don't seep into the wood though, and I find that using them generally causes the wood to tear off at the joints, leaving the top few grains bonded and tearing away underneath. Thinner is absorbed into the wood and thus hardens the entire joint.

I can't say in my experiences the thicker CA resulted in any stronger of a surface bond either.

But my bridges rarely failed at the joints.

Oh, and what do you mean by reinforcing? Going through and adding more glue to each joint, or just certain areas? I found that "reinforcing" each joint with thin CA could add about 2 g to the bridge, and if the joints were made correctly in the first place, it did little to increase strength.

[Aia]

My mantra with gluing is pretty simple: glue once, glue well.

I use a combination of the blue and purple CA glues, and I've found that there is an optimum amount of glue at each type of joint. Too little glue will not hold under stress, but excessive glue only adds mass to your structure. The key is finding the "right" amount of glue at each location and gluing only once, well.

How much glue mass do people have on their structure? I usually end up with .3g- .4g.

[cypressfalls Robert]

If anyone needs any help i found a really good website http://www.garrettsbridges.com i didn't really feel like searching this topic to see if anyone already posted it though....sorry if you have

[smartkid222]

http://picasaweb.google.com/smartkid222 ... 0022392354

In this picture there are 4 pieces of wood 1/8 x 1/16. Notice how the top 2 and the bottom one look fairly the same, but the 3rd one from the top is ligher in color. Is this b/c of grain or density? I dont' know much about grain which is why i'm asking this. Also can someone tell me what grain are these pieces? How can you tell?