Construction Updates 4
From Batcountry
See Construction Updates Part 1, Part 2, Part 3, Part 4, Part 5
Here we show Part 4 of our construction process for Bat Country.
Click on photos to enlarge.
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Bat Country Flyer
Print, cut, and fold to make your very own desk top tetrahedron. What's not to love?
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Tests of Strength
Some friends came over to help us prepare the other 300 bats we would need to build the full Generation 3 sculpture. Before we started working, everyone climbed the Gen 2 sculpture, except our good doggie Walter. Julie found a new way to hang on the sculpture.
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Here we check how straight the 4-bat bottom edge is with a group of people standing on the sculpture. The left photo was taken with five people on the top Gen 1 tetrahedron. No bend is visible. The right photo shows three men huddled onto and near the edge. A slight bend is ever so barely visible. This spot and the joints on the cement blocks are the points that receive the highest amount of stress from weight. That they stay straight with a lot of weight on the sculpture is very reassuring.
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We measured the deformation under a load of one man, checking the two types of most stressed points of the sculpture: The left photo shows the weight in the center of the 4-bat span. The right photo shows the weight at the corner.
Center of edge: 25 mil = 25/1000 inches = 1/40 inch = 0.635 mm
Bottom corner: 10 mil = 10/1000 inches = 1/100 inch = 0.25 mm
Considering the sculpture is made of steal and aluminum, a bit of flexing is to be expected. We are quite happy with this small amount of deformation.
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A constant concern of ours for Bat Country is its saftey as a jungle gym. We wondered what it might look like under failure of the bats, rods, or joints. Gwen made a scale model out of bugle beads, seed beads, and Fireline thread. When this model was accidentally crushed by a glutius maximus, it provided us a useful model for what a failure of the sculpture might look like. Two bugle beads ("bats") broke near the top. Other points of failure show where the model was not completely woven together. The weaving that is omitted could look like what might happen if a joining plate were to break into two, or were to break from a bat. The model sags but does not completely collapse. The design is so interconnected that it is difficult to break it completely into pieces.
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Drilling Is Messy
We've been working on this sculpture practically every day for three weeks now, so it was nice getting some help in the middle. We'd like to give special thanks to Stella, Bob, Julie, Marty, Thomas, and Greg for helping us with some of the less exciting parts of this project.
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Here's some of our waste. Cutting a couple inches off of the rods leaves little droppings. Drilling the aluminum bats created some really nice curley-cues. Here's a photo of some of the nicer pieces. Although the shavings are sharp, aluminum is so soft, they don't cut skin easily.
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We cored each bat from both ends with a hand drill. Then, we jammed a metal rod into the large end and banged it on the concrete until the rod emerged out of the handle end. A wad of polystyrene comes out with the rod. It feels like stiff foam. We later discovered that some of this banging jammed up the threads at the ends of the rods. Our friends helped us rethreaded them later.
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Centering Rods in Bats
Machine Man Dan helped us make a custom tool for tightening the bolt that hold the rods in place in the bats.
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Bat Country requires two different lengths of rod sticking out the ends of the bats: long and short. We need all four combinations (which we color coded for simplicity)
192 Red = short short
66 White = short head, long handle
66 Yellow = long head, short handle
60 Blue = long long
Once the rod is properly alinged in the bat, we used two of our special three-prong tools and a torque wrench to tighten each bat to 20 ft lbs.
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This completes Part 4 of Construction Updates.
Go on to Construction Updates 5.
All images, designs, and text on this site © 2005-2008 Gwen Fisher and/or Paul Brown. Permission required for any capture or reuse.
