Mathematics -- Build a homemade geodesic dome (2024)

A Geodesic Dome

Some years ago I built a geodesic dome out of ½ inch galvanized steelelectrical conduit, to serve as an aviary for chickens and small parrots.I wrote a computer program to calculate the proper lengths of steel tubing,and draw the diagram shown below:

The dome is made from three different lengths of tubing. I used coloredstickers on the tubes to mark the different lengths -- red for the long ones,violet for the medium lengths, and green for the short ones. You can see thosecolors in the drawing.

The ends of the tubes are smashed flat with a hammer, and then holes are drilledin the flat ends for a bolt to go through to connect up to six of the tubestogether. Aviary wire is then wrapped around the dome to keep the birds inand predators out. The completed dome is 18 feet high, and over 20 feet indiameter.

For this project, something a little more modest in size is required.Something less than three feet in diameter, so it can fit through a door.

For the first attempt at a smaller dome, I used bamboo kebab skewers andgumdrops. The three lengths of the struts are 100%, 97.85%, and 84.53%.Because I knew I would be using soda straw for the more permanent second version,and the straws were 7¾ inches long, I chose that length forthe long (100%) strut. That made the other lengths 7½ inches, and6½ inches.

You will need these materials for the gumdrop dome:

• 90 skewers 7¾ inches long
• 85 skewers 7½ inches long
• 80 skewers 6½ inches long
• 11 green gumdrops
• 15 orange gumdrops
• 50 red gumdrops
• Cellophane tape

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With the sticks all cut to the proper lengths (using a pair of wire cutters)the first step is to make the central pentagon of the dome. Five short sticks arestuck into a green gumdrop, and a red gumdrop is stuck onto each of the fiveends of the sticks.

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Next, five medium sticks are stuck into the red gumdrops, and the pentagon isno longer flat. We can now see that by making the sticks different lengths,we can ensure that the proper three-dimensional form will take shape.

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The dome is made of pentagons and hexagons. Each of the five sides of thepentagon has a hexagon attached to it made from the longest sticks. The sidesof the pentagons and hexagons are all made of the medium sticks. In the gumdropdome we have green gumdrops at the center of the pentagons, and orange gumdropsat the center of the hexagons, and red gumdrops everywhere else.

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When five hexagons have been attached to the central pentagon, and five moregreen gumdrops connected at the bottom between the hexagons, we have astructure that looks like a dome.

This is about as far as we can go with gumdrops alone. At this stage, all ofthe weight of the dome is being held up by the stickiness of the bottom gumdrops.But gumdrops can only hold a small amount of weight before the sticks start topull out.

We solve this problem by using cellophane tape to hold the sticks together.We only need to do it for the red and orange gumdrops, where we can easilyconnect the sticks in pairs, across the gumdrops. Attach one end of a 4 inchlength of tape to one stick, lay the tape over the gumdrop onto the oppositestick, and then fold the edges of the tape around the stick so the stickysides hold together. You can see this by enlarging the photo below.

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We end up with a nice dome. But it won't hold up well to being moved around,because the gumdrops are heavy and don't hold the sticks well enough. But itlet us get the concept, and it was nicely color coded.

Our second, more portable and permanent dome, is made from plastic soda strawsand small brads, the kind used for fastening paper.

You will need these materials for the soda straw dome:

• 90 straws 7¾ inches long
• 85 straws 7½ inches long
• 80 straws 6½ inches long
• 76 small brads

The first step is to cut all the straws to length.

Next, poke holes a quarter of an inch from each end of each straw with a sharpknife or an ice pick.

Next, make 6 five-sided stars (from the short straws),and 15 six-sided stars (from the longest straws) by sticking the brad throughthe ends of 5 (or 6) straws, and bending the ends of the brad over to securethem.

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We begin assembling the dome by connecting one side of the centerpentagon to one side of a hexagon. The photo shows one hexagon forclarity, but you will be putting two hexagons on at a time, so thereare always six straws meeting at each brad. The photo also only showsone medium length straw forming an edge, but you will be adding theedges on all sides, closing the brad whenever you have six straws connected.

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In the photo below, we have five hexagons connected to the central pentagon,and five more pentagons (without sides yet) connected between the hexagons.

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The finished dome is 2 feet 2¾ inches tall (68 centimeters).It is lightweight, and can be tossed around without breaking, and will fitthrough doors, or in the back of a station wagon. The geometry of thefinished sculpture is quite beautiful.

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The large dome is still housing chickens out in my backyard. It is amazinglystrong -- I had to climb all over it to wrap the aviary wire on it, and itnever budged.

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We put a small plastic shed (7 feet high, 6 feet long, 8 feet wide) next to it,and removed three struts to form a door, and screwed the aviary wire to the shed,so the shed forms a nice door and "airlock" so the chickens don't escape.

A large plastic tarp attached with bungee cords forms a waterproof roof.The small parrots live in the top half of the dome, and the chickens havethe bottom half.

A Paper Geodesic Dome

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The same ideas can be used to build a dome made from triangular sheets ofmaterial instead of rods. The edges of the triangles simply have the samelengths as the rods did.

If we choose to use paper, we can print out a template on a printer, andthen simply cut it out, fold it, and tape the edges together to get a dome.

You can print out the following page from the web site, or make a photocopyof it, enlarging it if you want a larger dome.

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If you want an even larger paper dome, you can cut the drawing into smallerpieces, so when your printer resizes them to fit the page, you will havelarger triangles. Use tape to reconnect the smaller pieces into one largepiece. In the drawings below, I have duplicated the central pentagon tomake it easy to see how they fit together. You will want to cut one pentagonaway before taping the pieces together.

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Click on photo for a larger picture

You can also cut the triangles out of cardboard or plywood, and tape themtogether, so that fiberglass can be applied to make a sturdy building.

Next: A Homemade Microgram Balance

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Send mail to Simon Quellen Field via sfield@scitoys.com

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