Originally Posted by
HillRider
Pliers aren't tempered nearly as hard as a good file or they would be too brittle to be used. That said, filing that much metal from a set of pliers will probably end the useful life of the file. A Dremel tool with a suitable grindstone would be faster.
The typical chrome plating on many of the slip joint pliers would tear hell out of the file first. Best to grind off the chrome first. Although these days the cheapies are likely just nickel or zinc plated.
Working the file with a bit more than normal pressure and taking slow cuts will also aid in shaping harder steels such as the jaws of pliers like this. If the worker just zips it back and forth like a steel version of sandpaper then it'll take the cutting edges off the file teeth pronto. And for anyone not all that file savvy that wants to try this trick remember that a file is like a wide saw blade because it has angled teeth that cut. So LIFT it on the return stroke and only push down on the push stroke to keep it operating at it's best for a long time.