A hollow spar can be made
from 8 identical pieces twice as wide as tall with a 90° birds mouth
notch taken out of one side. The so called birds mouth technique was
described in the Aug/Sep 1999 issue of Woodenboat Magazine. The drawing
above helps to see how the pieces go together and if the size of a piece
is x by 1/2 x the overall is 2.5 x.
(note:
This is only an approximate value; the actual being 1.5+1.5sin(45°)
x ~= 2.5606... x. For our purpose of making a round spar that will be rounded
the extra .06 x will be insignificant. That much will be trimmed off without
noticing.)
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