i did one once. i have machines, but do not claim to be a machinist. if you look close, it was not cut with a beveled mill cutter, but cut with a normal endmill bit, diving down at about 10
clock, and then move over and do 2 o clock (just guessing) look at it, and you will see the cut from ford left sort of a "w" shape in the spline. i too thought they had a cutter that shape, but no, i believe its done with a straight end mill. perhaps some real machinists can expand