Things You'll Need
Fine metal file
Sheet metal cutting shears are used to cut sheet metal into specific shapes for special building projects. The shears are sold equipped with razor-sharp blades from the factory. However, after extended use, these blades can dull and become ineffective; they must be sharpened periodically to ensure that they function properly. Many methods may be used to sharpen sheet metal cutting shears, some of which require specialized tools. However, the work may be done with a set of common metal files.
Remove the blades from the shears. How to do so will vary depending on your model of sheet metal cutting shears. All models use mounting bolts to secure the blades in place. Use a hex key of the appropriate size to remove the bolts. Some models may require additional steps and the use of other tools, such as an adjustable wrench. Consult your shears' instruction manual for exact directions.
Secure one of the blades in the bench vise with the edge to be sharpened facing up.
Place the file against the to-be-sharpened edge of the cutter blade. The file must be perpendicular to the blade. Tilt the file to follow the angle of the blade's factory bevel; this is usually between 30 and 45 degrees.
Apply pressure and move the file along the length of the blade in an even stroke away from you. This forms a burr, or lip, on the back edge of the blade. Continue applying the strokes until you have a clean, sharpened edge on the blade.
Tape a piece of 300-grit sandpaper to a flat surface.
Remove the blade from the vise and rub the blade side with the burr on the sandpaper. Carefully feel the back of the blade to verify that the burr is gone.
Repeat the steps on the remaining blades. Some shears have two blades while others have three.
Reassemble the sheet metal cutting shears according to the manufacturer's instructions.
Some models require adjustments when installing the sharpened blades. Some manufacturers suggest lubricating the shears while they are disassembled.
Do not moving your hand parallel to the blade when checking for the burr to avoid cutting yourself.