Self-Supporting Dome Construction

Background stuff: see ArchDomeConstruction

The reading by Savadori02 is particularly relevant, as are various parts of King00.

N.B. The shape of the blocks matters -- they need to be sections of a spherical shell. Like the voussoirs of a roman arch, they need to be wider at the outer surface than at the inner surface. This makes it impossible for them to fall inward.

Q: How do we measure all the appropriate angles? How did the original masons do it?

The foam dome solution:

  1. Order some giant styrofoam hemispheres from a place like Shape Formation
  2. Cut them into wedges and then scoop out the inner part of each wedge and chop them into pieces -- using a hot wire and some very simple fixtures
  3. Add some "spiral" geometry to help make each row self-supporting (a crude approximation to Brunelleschi's elegant herringbone pattern).

Manufacturing lessons learned:

  • It takes a long time to measure and cut 4x16x4 foam pieces, even with a hot wire
  • Tolerances stack up. The wire has finite width and the fixtures are imperfect so one cannot assume rotational symmetry.
  • Therefore one must number the parts to create a 3D jigsaw puzzle
  • The spiral arc idea is a bit tricky -- the angle of inclination of the spiral should really change as a function of where you are on the sphere
  • Coating the foam blocks with clear acrylic (water based) varnish helps make them sturdier.. (but use a non water-based marker smile

-- MarkCutkosky - 18 Jan 2005

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