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Practical Joining Systems
The pine-panelled soccer ball
shown on the Versions Page uses butterfly-shaped keystones to join panels.
These taper towards the origin at the centre of the ball. Tapered
dovetails of similar geometry don't work. Not only can the panels
not be joined
together, but also they can't be taken apart if ever joined in the first place.
You can verify this in L3DD by trying to move one component panel
radially outwards. The panel would jam, as 3D solid-solid overlapping
occurs. All is not lost, however, as conventional, parallel-sided dovetails can be made to work if
attention is given to the way the dovetails are arranged on each edge,
and the order in which the panels are assembled.
In version 3.50 of Ligno3D designer we introduced a system of
dovetailing that works on most "reasonable" polyhedra (e.g., SoccerHead).
The dovetails can be cut with
conventional tools, without the need for expensive,
computer-controlled, multi-axis routers.
In the pinewood dodecahedron on the right, the top face
is the
last face to be inserted. It has five sets of twin female dovetails
showing on its outer surface. Face number one (not seen here) is free of
female dovetails, while all other
faces have between one and four sets, depending on how many adjoining
faces are in already place when the face is added to the assembly. There are 4 faces with
4 sets, 3 faces with 1 or 2 sets, one with 0 or 5 sets, and none with 3
sets.
All dovetails are cut so that their sides are
perpendicular
to the faces they penetrate. In this way, all faces, including the
last one, can be easily inserted by sliding them inwards along their cut dovetail
surfaces.
This system of dovetailing is completely general and can
be applied to most types of "reasonable" polyhedron. For
triangular faces the twin dovetails should be closer together, and further
away from the face's vertices. Single dovetails can be used, and
the the size of the dovetails can be varied.
The dovetailed panels are automatically assigned a component name such as "DT Panel
7".
They can be selected by double clicking with the left mouse button, and moved as a
single entity. To avoid very messy 2D plans, one should be very selective
about what faces to show in the plans. Each panel is made of many
faces.
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The cut surfaces of butterfly keystones, when projected, intersect at the
origin (origin centric).
Dovetails are cut perpendicular to the faces
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