Cut screw without damaging the threads

[kalubah]

I have the impression that I learned if you cut a screw, you destroy the threads.
Yesterday, I needed a shorter screw than what was available in the hardware store. The guy there suggested I buy a longer screw and snip it off. He looked like a birdhouse when I said that it wasn't possible. So how is it now? Can you shorten a screw and how do you do it? Saw, snip, file, or something else?
In this case, it's about a pretty fine-threaded situation of the type you have in a junction box cover.

 

[Hubbe2]

Cut off just above the proper length, then file down the last millimeter. IF you don't have access to a nut, the absolute best is to thread a nut on, saw off in front of the nut, and then unscrew the nut; it will clean up the thread.

 

[Skumpen]

Saw off the screw to the correct length and make a chamfer 1*45 degrees.

 

[tjaboo]

I usually make a gang cut first and then bevel the top, if I use a file I only file towards the screw, with a dremel and sanding drum you just go ahead.

 

[hempularen]

As mentioned, saw with a hacksaw, I have also used a metal saw blade in the jigsaw. Then a few strokes with the file to smooth out the edges.

However, it's not ideal to cut the screw. If you do, you should probably thread it in and tighten first. Then cut it off and hope you never need to loosen the screw.

I have, a long time ago, seen pliers where you could thread screws up to M5, and then the screw was sheared off when you squeezed the pliers.

 

[AndersS]

As mentioned, cut with a hacksaw; I've also used a metal saw blade in the jigsaw. Then a few strokes with a file to tidy up the edges.

However, it's not ideal to cut the screw off. In that case, you should probably thread it and tighten it first. Then cut it off and hope you'll never have to loosen the screw.

I have indeed, a long time ago, seen pliers where you could thread screws up to M5, and then the screw was sheared off when you pressed the pliers together.

They were found on the simpler types of crimping pliers, but it wasn't ideal.

 

[prototypen]

The screw cutting on the "crimping pliers" is almost the only thing they're good for, as it works according to the die/nut method. Thicker screws are sawed off and the ends are beveled 60 degrees, the same angle as the thread flank (yes, I know that Whitworth and pipe thread are 55 degrees).

Protte

 

[raveper]

Here you can find screws that you can cut with pliers, easy as pie. http://www.jula.se/skruvar-for-dorrhandtag-2-pack-123820

 

[Forbo]

Dremel, multimaster, hacksaw...put a nut inside the saw cut. Saw...unscrew the nut...done.
(*** how much I've cursed before I discovered the simple method...then the sinner shall learn...)