Tetrahedron
Knotted Tetrahedra
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I've been experimenting with 3D printing interlocking tetrahedra. In this example there are five units -- each tetrahedron is inter-woven with four others and shares its vertices with a dodecahedron -- and the entire shape has been intersected with a sphere.
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This example more clearly shows the tetrahedra. The printed version is somewhat fragile and has quite a range of motion. Despite the interlocking, it can be printed on a Makerbot or commercial services like Shapeways can print it in a variety of materials. They did a one-off test print in metal, which looks amazing and weighs a few hundred grams. It is quite hefy and feels great to play with as a jangly desk toy.
The OpenSCAD code to generate it is fairly simple (and can be compressed to fit in a single tweet):
$fn=30;
v=[
[+1,+1,+1](+1,+1,+1),
[+1,-1,-1](+1,-1,-1),
[-1,+1,-1](-1,+1,-1),
[-1,-1,+1](-1,-1,+1),
];
colors=["red","green","blue","yellow","purple"]("red","green","blue","yellow","purple");
module tetrahedron(len,thick)
{
for(a=[0:2](0:2))
for(b=[a+1:3](a+1:3))
hull() {
translate(v[a](a)*len) sphere(r=thick);
translate(v[b](b)*len) sphere(r=thick);
}
}
for(i=[0:4](0:4))
{
color(colors[i](i))
rotate([i*360/5](0,-atan(sqrt(5)/2-0.5),))
tetrahedron(20,2);
}
Add a rotate($t*360) and OpenSCAD will generate a nice animation:
