
Cardboard is free, but I have not found a way to waterproof
it sufficiently (BUT, IT BURNS!). These shelter domes were conceived
to help the homeless and refugees. I have tried a variety of methods for
waterproofing and fire retardation, without great success. The upside
is, you can decorate them any way you want!
First you need to know how to draw a proper
triangle, of course, if you have had drafting 101- you can skip
this part.
Start with a point(a), with a
compass, scribe an arch of a
given radius. At any place on this arch make a point(b) , put
your compass, set to
the radius of the arch on that point, draw a short, intersecting arch,
this is
point(c). Connect these three points.


This is an
equilateral
triangle

Nothing
like having supervision!
The isosceles triangle is a little different. The pentagons consist
of
isosceles triangles. Draw a line point(a) to point(b) a given length(A),
set the compass a given shorter length(B). At one end of the line,
place the set
compass, draw a short arch making sure it passes over the center point
of the line.
Now go to the other end of the line, place the compass and draw the
intersecting
arch. That intersection is point(c), Connect (a),(b) and (c).


This is an isosceles triangle.
TIP: If you need a real big compass, use a 1" x 3" board. Run a drywall
screw through it about an inch from one end then mark your strut lengths
and drill holes (centered on the board)
that a pen will fit in (snugly).
You can use one board for both strut lengths.
Now you can draw really big archs for larger triangles.