DODECAHEDRON TABLE LAMP
makezine.com/11/primer
START WITH A CRYSTAL
Because none of the Platonic solids, except for the
cube, contains obvious 90° angles, building them is
a counterintuitive, mind-bending experience. Before
we get to the dodecahedron, let’s warm up with
something simpler: an octahedron.
You can make this in a few minutes using 12
plastic cocktail straws and 6 squares of duct tape,
laying them out as in Figure B. Circle the straws
around so that point A sticks to point B. The
squares of tape should bend like hinges while
the straws remain straight.
Now hinge the vertical straws so that their A
points C all meet together at point D. Again, keep
the straws rigid, and flex the tape. Turn the
structure upside down, bring points E to point F,
and the result should look like Figure C. To prevent
the straws from coming unstuck, you can bend
the tape inward so that it sticks to itself.
Octahedrons are a common structure on the
molecular scale, and because a crystal grows by
repeating itself, tiny octahedrons assemble to form
big ones. Search for “crystal octahedron” on eBay,
and you’ll discover that rockhounds know all about
Platonic solids.
Notice how rigid your drinking-straw octahedron
is. In fact, its shape is so efficient that it can support
as much as 1,000 times its own weight. This suggests how rocks and metals achieve their strength.
Fig. A: The five Platonic solids: tetrahedron ( 4 sides),
hexahedron ( 6 sides), octahedron ( 8 sides), icosahedron
( 20 sides), and dodecahedron ( 12 sides).
FROM 8 TO 20 TO 12
Let’s try something a little more permanent than
drinking straws and duct tape. You’ll need 8' of
10-gauge, solid copper wire, and 60 electrical ring
terminals, size 12– 10. (Within this terminal size
specification, if you find a choice of ring sizes, select
the ones with the smallest holes.)
Begin by hammering a couple of finishing nails, 3¾"
apart, into a block of scrap wood. Now cut a piece of
wire 3" in length, use pliers to pull the plastic shields
off 2 ring terminals, and slip the terminals onto the
ends of the wire. Place the assembly over the nails to
hold everything in position, and solder the terminals
onto the wire with a 30W (minimum) soldering iron.
After you do this 30 times, you’ll have enough
components to build the icosahedron shown in
Figure D. You can use 2" #10 bolts to join the ring
terminals, which you’ll have to bend slightly to
make them align with each other.
Now here’s the interesting part: if you disassemble
the icosahedron, you can build the dodecahedron in
Figure E using exactly the same number of pieces
of wire because both solids have the same number
of edges.
You’ll find that the icosahedron is very easy to
build, as the triangles cannot be deformed. The
dodecahedron is very difficult because its pentagonal sides collapse easily. Therefore we’ll need
to fabricate our dodecahedral table lamp from a
material that has its own rigidity, such as plywood
or (my personal preference) ABS plastic (see MAKE,
Volume 10, page 100, “Plastic Fantastic Desk Set”
for an intro to working with ABS). Since we’ll put
a cool-burning fluorescent bulb inside the lamp
to avoid overheating it, our dodecahedron must
be big enough to contain the bulb. The suggested
minimum dimensions are shown in Figure G.
If you’re wondering how to cut a symmetrical
pentagon, there’s an easy way and there’s a harder
way. The easy way is to draw a pentagon using
vector-graphics software such as Adobe Illustrator,
then print the pentagon and use it as a template.
(Old versions of Illustrator are cheaply available on
eBay and will run on Windows versions up to XP.)
The harder way is to use a pencil, paper, and
pro-tractor. Whichever way you do it, the inside
angle at each point is 108°, and each side is angled
72° from each previous side. (CRAFT magazine,
Volume 04, page 96, “Repeating Splendor,” has step-by-step instructions for drawing polygons with any
number of sides.)
166 Make: Volume 11
