i never have the right length screws or bolts and am always needing to shorten them. here is a
trick. place the length to be cut off in the vise so you don't mangle the threads of the piece you
want. Make sure you have placed a wingnut or nut of some description on the end you wish to
keep. Later you wind this off to clean up the threads so you don't need to re-die the screwthread.
Step 1: Place Nut or Bolt on Threads.
Step 2: Mark Cut and Place in Vise.
Step 3: Hack Saw Off.
or dremel for hard steels and larger diameters.
When you are finished wind the nut off and in that process the thread will be fixed by the nut as it
comes off. It wont be perfect but it will prevent cross threading and make starting the thread a lot