One additional thought is for a threaded steerer tube - screw on a headset top cone before making the cut.
Use whatever method you like to cut the tube - a Park(or other ) guide and a very sharp hacksaw blade are my choice.
After the cut, remove any burrs, and burnish the top of the fork with a file.
Unscrew the the headset cone to clean up the threads.
The old adage of measure twice/cut once holds very true for this.