Files can be used to shape metal, to remove sharp edges and for sharpening things like saws. They are lengths of hardened steel with rows of tiny teeth cut into some or all of the faces. Files come in different shapes and sizes and with different types of teeth for particular tasks large coarse teeth are suitable for rough shaping or fast removal of soft metal, since they do not clog up easily. Small line teeth are suitable for smoothing edges when a good finish is required.
The teeth of a file are described by its cut. A single-cut file has sharp parallel ridges which run the full width of the file but at an angle to it. This type of file is good for sharpening tools. A double-cut file has two crossed sets of ridges giving small individual, diamond-shaped teeth. It removes metal more quickly than a single-cut file.
The file grade is a measure of the size and spacing of the teeth. Dead smooth files have the finest teeth followed by smooth, second-cut, bastard and rough. The different grades might have slightly differently shaped teeth, and the size of the teeth increases with the size of the file as well as with the grade. A second-cut file will be suitable for most purposes: coarser grades are better for removing metal particularly soft metals – quickly; finer ones are better for finishing hard metals. Rasps can also be used on wood.
The most common shapes of file are rectangular, round, half-round, square and triangular. Not all cuts and grades are available in each shape.
Flat files are rectangular in section, with double-cut faces and single-cut edges, and get narrower towards the point. Thin, more pointed versions with fine teeth are used for cutting keys and known as warding files.
Hand files are similar to flat files but get thinner towards the point, not narrower, and have one edge with no teeth, making them useful for widening a slot without deepening it as well. A very narrow hand file is known as a pillar file.
Half-round files have a double-cut flat face and a single or double-cut round face. They are for general use.
Round files are for use on concave surfaces and holes and are usually single-cut. Small ones are often called rat tails.
Square files are for cutting slots and getting into square corners. They have four double-cut faces.
Triangular (or three-square) files have three double-cut faces which are the same width. Knife files are similar but have one narrower single-cut face.
Saw files are usually triangular and are single-cut. A mill saw file is flat with one or both edges rounded and is useful for sharpening axes and saws with large teeth.
Very small files called needle files are used for precision work. They have their own integral handle instead of a tang and the cutting point is usually only about 75mm long and 3 to 6mm wide.
Using files
Files are very hard and tend to be brittle so they should never be abused:
– never use a file as a hammer or lever
– it could snap dangerously
– treat a file with care, do not let it get rusty or rattle around in a tool box both things will blunt the teeth
– never use a file without a handle and always use handles with ferrules. The tang of a file is very sharp and could dig into your hand or body. To fit a handle, grip the file in a vice and knock the handle on to the tang with a mallet. Make a hole in the handle first if it has not got one
– clean out teeth clogged with metal or dirt by stroking a file card across the file. File cards are wire brushes with short, hard bristles.
