This is a very cool site that contains drawings a ton of polygons. It also has 3D color pictures that can be rotated of polyhedrons of varying complexity, I found one that looks like the Epcot center.
On to the goods
1.) Omni Cork Plug
2.) Put a screw in the bottom of a 1x1 cylinder and hold it verticly
^ (when its done) sorta like that drawn and mill out the triangle shape.
3.) Extrude a 1in. Dia. Cylinder, with a 60 deg. taper, 1in.
Looking at
this site i described above i noticed that on the square face the piece removed by the triangle is a perfect parabola.