A common misunderstanding about bolt cutters is that they have extraordinarily sharp blades which can only be sharpened with special tools. In reality, their cutting power comes from the enormous mechanical advantage generated by their lever-like handles. The blades themselves can be sharpened using techniques familiar to anyone used to taking care of their own tools.
Things You'll Need
Check the bolt cutter's head for filth. Wipe or scrub away anything that is excessive and would interfere with sharpening or with the workings of the bolt cutters. A rag with a little soap and water will probably be enough to take care of this. Dry off the cutting blades afterward.
Place the bolt cutters across your lap so that they are in the open position with the blades pointing away from you and in a stable position.
Working with one blade at a time, place the mill file against the bevel at a 20 to 30 degree angle, matching it as closely as possible. Push the file down and along the face of the blade. Repeat this motion seven to 11 more times, and then do it again for the other blade.
Turn the bolt cutters over and file the other side of each blade for eight to 12 strokes in total, making sure to get any burrs off the blade.
Put two to three drops of machine oil on each blade and rub it in with a dry rag. This will help protect your blades against rust.