Building a Geodesic Dome Model

Get Ready to Build a Geodesic Dome Model

Before we begin, it's helpful to understand some concepts behind the construction of the dome. Geodesic domes are not necessarily built like the great domes in architectural history. Geodesic domes are usually hemispheres (parts of spheres, like half a ball) made up of triangles. The triangles have three parts:

• the face — the part in the middle
• the edge — the line between corners
• the vertex — where the edges meet

All triangles have two faces (one viewed from inside the dome and one viewed from outside the dome), three edges, and three vertex. In the definition of an angle, the vertex is the corner where two rays meet.

There can be many different lengths in edges and angles of vertex in a triangle. All flat triangles have vertex that add up to 180 degrees. Triangles drawn on spheres or other shapes do not have vertex that add up to 180 degrees, but all the triangles in this model are flat.

If you've been out of school for too long, you might want to brush up on the types of triangles. One kind of triangle is an equilateral triangle, which has three edges of identical length and three vertex of identical angle. There are no equilateral triangles in a geodesic dome, although the differences in the edges and vertex are not always immediately visible.

As you go through the steps to make this model, make all of the triangle panels as described with heavy paper or transparencies, then connect the panels with paper fasteners or glue.

Step 1: Make Triangles

The first step in making your geometric dome model is to cut triangles from heavy paper or transparencies. You'll need two different types of triangles. Each triangle will have one or more edges measured as follows:

Edge A = .3486
Edge B = .4035
Edge C = .4124

The edge lengths listed above can be measured in any way you like (including inches or centimeters). What is important is to preserve their relationship. For example, if you make edge A 34.86 centimeters long, make edge B 40.35 centimeters long and edge C 41.24 centimeters long.

Make 75 triangles with two C edges and one B edge. These will be called CCB panels, because they have two C edges and one B edge.

Make 30 triangles with two A edges and one B edge.

Include a foldable flap on each edge so you can join your triangles with paper fasteners or glue. These will be called AAB panels, because they have two A edges and one B edge.

You now have 75 CCB panels and 30 AAB panels.

The Reasoning

This dome has a radius of one. That is, to make a dome where the distance from the center to the outside is equal to one (one meter, one mile, etc.) you will use panels that are divisions of one by these amounts. So, if you know you want a dome with a diameter of one, you know you need an A strut that is one divided by .3486.

You can also make the triangles by their angles. Do you need to measure an AA angle that is exactly 60.708416 degrees? Not for this model, because measuring to two decimal places should be enough. The full angle is provided here to show that the three vertexes of the AAB panels and the three vertexes of the CCB panels each add up to 180 degrees.

_{AA = 60.708416
AB = 58.583164
CC = 60.708416
CB = 58.583164}

Step 2: Make 10 Hexagons and 5 Half-Hexagons

Connect the C edges of six CCB panels to form a hexagon (six-sided shape). The outer edge of the hexagon should be all B edges.

Make ten hexagons of six CCB panels. If you look closely, you might be able to see that the hexagons are not flat. They form a very shallow dome.

Are there some CCB panels left over? Good! You need those too.

Make five half-hexagons from three CCB panels.

Step 3: Make 6 Pentagons

Connect the A edges of five AAB panels to form a pentagon (five-sided shape). The outer edge of the pentagon should be all B edges.

Make six pentagons of five AAB panels. The pentagons also form a very shallow dome.

Step 4: Connect Hexagons to a Pentagon

This geodesic dome is built from the top outward. One of the pentagons made of AAB panels is going to be the top.

Take one of the pentagons and connect five hexagons to it. The B edges of the pentagon are the same length as the B edges of the hexagons, so that is where they connect.

You should now see that the very shallow domes of the hexagons and the pentagon form a less shallow dome when put together. Your model is starting to look like a "real" dome already, but remember — a dome is not a ball.

Step 5: Connect Five Pentagons to Hexagons

Take five pentagons and connect them to the outer edges of the hexagons. Just like before, the B edges are the ones to connect.

Step 6: Connect 6 More Hexagons

Take six hexagons and connect them to the outer B edges of the pentagons and the hexagons.

Step 7: Connect the Half-hexagons

Finally, take the five half-hexagons you made in Step 2, and connect them to the outer edges of the hexagons.

Congratulations! You've built a geodesic dome! This dome is 5/8 of a sphere (a ball) and is a three-frequency geodesic dome. The frequency of a dome is measured by how many edges there are from the center of one pentagon to the center of another pentagon. Increasing the frequency of a geodesic dome increases how spherical (ball-like) the dome is.

If you would like to make this dome with struts instead of panels, use the same length ratios to make 30 A struts, 55 B struts, and 80 C struts.

Now you can decorate your dome. How would it look if it were a house? How would it look if it were a factory? What would it look like under the ocean or on the moon? Where would the doors go? Where would the windows go? How would the light shine inside if you built a cupola on top?

Would you want to live in a geodesic dome home?

Edited by Jackie Craven