360 divided by 20 equals 18
The inside cut angle should be 20 degrees

Keith

"Bruce White" wrote in message
...
I tend to look ahead at projects, and when I get an idea, I think about it
a
while. I am wanting to make a piece that will require an icosahedron at
it's core to turn into a ball. My triangles will be 20 identical
equilateral triangles with 5-1/4" "legs" at 60 degrees, (I may make this
smaller, I haven't decided yet). These will all be glued together and
should form a icosahedron approximately 7-3/4" in diameter, which isn't
critical, I can live with just about any size over 6". This part I
understand. Now here's my dilema...

These triangles will be made of 3/4" thick lumber, and I need to figure
out
what the angle to cut the inside miters on the triangles so they all glue
together nice and snug into a roundish type of structure.

Any help??

Bruce