| Ligno3D Designer (L3DD) is very good for designing geodesic
domes like Andy's dome shown opposite. The framework
members here are made in two halves that are joined along their
lengths. L3DD generates 'split
frameworks' from almost any polyhedron (e.g.,
SoccerHead). The outer framework
faces parallel the faces of the polyhedron. This type of frame
can be sheathed in panel material such as construction plywood.
Indeed, the triangular panels can be framed before they are bolted
together, thus making a marvellous prefabricated portable structure.
With L3DD the structure
need not be
hemispherical. It can be taller,
squatter, or
even ellipsoidal.
L3DD's 'Create Frame' command can now make both split
and rectangular frameworks.
The latter option converts
convex polyhedrons into frameworks made of members with rectangular
cross-sections, with the width and
depth of members specified. Such a framework can be easily built from
standard timber sizes (eg. 4" x 2"), using just a protractor,
pencil, steel tape and
handyman's cut-off saw.
Rectangular frameworks are organised so that the outer faces of the frame parallel the chamfered
edges of the original polyhedron. For example, a framework
created from a cube has the outer framework faces oriented at 45
degrees to the cube faces - as illustrated on the right. Such
a frame could be covered with canvas or vinyl sheeting.
Alternatively, angled grooves could be machined to house thicker
face panels.
To obtain angles for cutting the
frame joints, only the outer faces of the framework should be drawn
in the 3D and Plan Views. To achieve this, enter a frame depth
of zero. 'Origin-centric' angles must be specified in the Plan
Setup dialog box, as half-interfacial angles may not do the job.
With origin-centric angles, the planes of the V-shaped end cuts,
when extended, all
pass through the origin. Perfect joints can be made by
accurately reproducing these solid angles in the timber.
As shown on the right, L3DD now generates very
precise rectangular frame members that fit together perfectly at the
joints. They do not interpenetrate (version 3.51 on).
When printing plans, however, follow the zero-frame-depth advice
given above. When all faces are selected, the plans become
very messy, with eight faces per frame member. All frame
members are assigned unique component IDs.
See also Designing Geodesic
Domes and Workshop. |
L3DD-designed model dome by Andy
Martinez, Florida, USA. He
has now made a big
hurricane-proof one!
L3DD V3.40 orients the frame's outer faces parallel to the
'chamfered' edges of the original polyhedron.
Icosahedral rectangular frame with one member moved.
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