Originally Posted by junkyard
for the machinists out there....well jim and ret
can you mill a square tapered hole to fit onto a 3piece bottom bracket?
It's called a broach. You drill a hole first, and then use an arbor press to push a broach into the hole. The broach shaves the metal out of the corners. This is also how straight key slots are cut.
It could also be done with a wire EDM, but it would be expensive.
The milling machine will always leave a radius in the corners.