I've cut alloy steerers - new blade, mitre box, measure 3 times, saw, job done - but what's the best thing to cut carbon ones with?
I'm concerned about delaminating the edge, and I know to wear a mask. I like my lungs to work!
A whack with a fecking great hammer and a cold chisel is as good as anything, but if you want to do it the namby pamby mechanics way then use a new, good quality hacksaw blade. A bit of insulating tape over the cutting area is said to stop the lacquer chipping off as you saw, and a bit of emery to clean the edge up afterwards.
For a straight clean cut use an old stem as a guide.