Here I sit - fixed -
While worlds around me spin.
Unsupported, hanging - yet
Supported by - nothing.
Vastness, space around me spreads,
No up or down or right or left
All merges into one, whole,
Yet of the air my dreams are made,
Like birds they soar into the sky.
I reach for the clouds, the air, my dreams.
I fall short.
They soar too high.
Here I sit - fixed -
Now you too can build your very own model bridge!
(As if you'd want to. )
I just thought it might be interesting to show you how I go about building a bridge. Of course, it may not be interesting either. It just seems, in my experience, that most people have no concept for how to... well... build a bridge. Well, I wouldn't either if it hadn't been for Ben and Dad. So thanks, guys.
The very first thing that I start out doing is laminating 3/32 inch square basswood sticks together. To do this, I use the jig Dad so graciously made for me which holds the pieces together while the glue dries.
Basically, the jig is composed of a long board with two boards glued/nailed on top of it with a gap in between. You can see it in the picture.
I put one piece of wood into the gap, put a thin line of super glue down the length of it, and then put the other piece of wood on top.
And, to keep the super glue from sticking to the jig, I actually put waxed paper down in the gap around the basswood pieces.
I then press both basswood pieces down into the gap, clamp another board on top, and wait a couple hours for the glue to dry. That's why I do this step first!
When I come back and take the basswood out of the jig, I have two pieces nicely laminated together.
To actually start to build the bridge, I first cut out the major pieces, referring to my as-accurate-as-I-can-possibly-be, actual-size drawing.
Usually I cut out two pieces at a time, one for each side, so that they're exactly the same. That's why I use the tape - to hold the pieces together while I'm sawing them.
Usually I have pretty good success just freehanding the sawing. I just draw a line at the right angle and length and hope for the best!
Here you can see the main pieces I cut out. Notice that there are two of each piece.
Then I have to figure out how to hold everything in the right place while I glue the pieces together. Right now I'm just making a quick and dirty model, just to see how the real bridge will act. So for this little guy, I just held the pieces on my drawing as I glued them.
There you can see all my pieces drying.
And that's all that's going on right now. I talked to Ben and Dad about my design today, and I think I have a pretty good idea what I'm going to do. Thanks, Steve for all your input too. I like your idea about my trouble joint, and I think I'll incorporate some of that into my design.
The three hundred millimeter gap, to be precise.
Ok, Ben and Steve, I have some more work for you. :D If you don't feel like exerting your brain, though, don't worry.
I am liking Ben's suggestion about my trouble joint the more I think about it.
First of all, here's a picture of my shorter design.
The members are marked in black, and the joints are marked in red.
Basically with the "problem joints" (joints 1 and 5), I'm thinking I should glue members 1 and 2 on top of member 6. Of course, I will have to put a little block of wood in there to fill in the gap. You might be able to see what I mean from the pictures. The turquoise member is member 1, the yellow member is member 3, the purple/blue member is member 6, and the little red member is the little block of wood to fill in the gap.
I hope you appreciated that picture; it took me a lot of effort to try to get it to look right. The yellow member isn't quite right still...
The next picture is what the joint would look like if you looked down the length of the bridge.
Sorry about the blue and red members; I think I will put the blue member right next to the yellow one, just so the yellow member can have more direct contact with the blue member. I guess that means that my first drawing is wrong.
This afternoon I got out all my old bridges to see what similarities in design I could find. Last year's bridge deals with my joint 1 problem.
As you can see, the long members across the bottom just snapped off the long members going up to the loading point.
This bridge is from two years ago, and it actually won first place! And once again, that trouble joint is what made it fail.
The long members across the bottom snapped off of the long members going up to the loading point. The interesting thing to note about this bridge is that it is asymmetrical. The loading point is offset from the center of the span, like this year's bridge. On this bridge, however, the loading point is offset by 100 mm, and this year's bridge is only offset by 50 mm.
This bridge failed on the shorter side, the side with the greatest angle, and the side with the most load. This will be true of this year's bridge as well.
So, to sum it up, I think putting members 1 and 2 on top of member 6 will definitely help my problem. I'm still thinking about how members 3 and 4 will fit into the picture.... (not literally)
This next bridge is from my first year at the bridge contest. Actually, it's the bridge I sent to the international contest, and yes, the bridge is broken in the picture, and no, you're not seeing what I actually sent in. Some members are missing.
This bridge has something interesting that I think I might be able to apply to joints 2 and 4.
See how the bottom member actually fits into and becomes a part of the upper member? I think I might be able to use that same idea in this year's bridge in joints 2 and 4. I think it would add strength to the joint that I wouldn't get if I just glued members 3 and 4 to the outside of the member under the loading plate. (?)
Another thing to notice about this bridge is how it used vertical members very similar to member 5. The joint connecting that member to the loading point snapped in this bridge, and I'm wondering what I might do to keep that from happening to this year's bridge.
And finally, just a picture of my favorite bridge and the one that won third in the international bridge contest two years ago. This picture is actually a test bridge I built before I built the bridge I sent to the contest. Unfortunately, they didn't send my bridge back after the contest, so I'll never know where it actually broke. I can push on it pretty hard, and it won't even budge! Pretty cool.
Well, hopefully not. :)
So, here begins my build-a-bridge-in-two-weeks-because-you-didn't-get-around-to-starting-it-sooner marathon. I am such a procrastinator.
Ben, here is what I'm thinking about right now. If you could let me know your thoughts on the design, I would really love it. (I'll even make some more cookies for you when you come home again. :D)
You can click on the picture to enlarge it.
Basically I'm thinking that I'm going to go for a big, heavy (and hopefully strong) bridge this year. Fortunately, the weight limit is 30 grams instead of 25 grams. It'll help, but this is still going to be a scale-full.
I'm thinking of doing members 1, 2, 3, and 4 with fours (four wood pieces laminated together). Member 5, I'm thinking I can get away with using a two (two pieces laminated together), especially since it will only be in tension. That'll give me some good surface area at the top corner joint as well. Member 6 I think will probably be ok just being a single piece of wood (?), but I might want to beef up the corners where the bridge touches the support surfaces. Those two corners are going to be under a lot of stress. First of all, you have the tension from member 6 and then the forces trying to push outward from the big members coming down. So basically, pretty much all the force exerted on the bridge is going into those two corner joints. It makes me scared. Another thing that's scaring me is members 3 and 4; they just seem so likely to snap off where the load is being applied (the red box and arrow). Do you think they'll be ok without any other support from elsewhere? I don't really know a logical place to even support it. I suppose I could put something between members 1 and 3, but I'm really not sure if it's essential.
Anyway, just some of what I've been thinking about. Ben, if you could give me some feedback (unless, of course, you're too busy :D), that would be totally awesome.
Anyone else can comment too. :D Especially if you notice something I didn't!