A mill or an angle grinder is good, but I use the truest of precision instruments: hammer and cold chisel.

Okay, jk. I use a hacksaw with a new blade in it and cut twice. Before cutting, drill a hole at the end to reduce the chance of cracks forming. Starrett 32 tooth blades are the gold standard, but I am pretty happy with Lennox. A good saw frame is necessary to tighten the blade sufficiently that it doesn't wander. You should be able to clean up with a file if you get off-track. Some people use two blades, but I have never convinced myself to try that.