Originally Posted by Creative Engineering
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.
you said the magic word....expensive
ok even tho i love the clean look of the bottom bracket jackshaft im probly gunna try to use a steel hub like i did on my electric drive conversion
thx for the info