How the joint works:
In searching for a form that was not rectilinear or triangular,
Robert Frazier experimented - until he realized that the edges
of a tetrahedron are the diagonals of a cube. By drawing diagonals
on to a cardboard box, he could see a simple way to build a
tetrahedron. From there, he envisioned the diagonals meeting
in a vertex to make an edge-lapped joint in three dimensions.
An interesting feature of the tetrahedral
joint design (patent #6132129) is that it can be made over
a range of angles from obtuse to acute in a variety of materials.
In glass topped tables, the elements are locked together by
gravity as well as from below by a peg in the center; in the
stools, the elements are locked together by the seat, which
is screwed to the legs and by steel rods used as rungs.
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