The file is a basic tool, but it would be a mistake to call it simple. Files come in a variety of shapes, cuts, and coarseness depending on the job they’re designed to do.
Whether you’re sharpening tools or cleaning up rough edges, choosing the right file starts with knowing the basics.
Most files come in 4 basic cuts: smooth, second, bastard (originally called a “Barsted” file, after its English inventor), and coarse. The cut describes the size of the teeth, with smooth cut being the smallest, and coarse cut being the largest. Large teeth will leave behind a rough surface, while small teeth will leave a smooth surface.
File teeth also come in single cut and double cut varieties. Single cut files have one set of parallel teeth, while double cut files have a second set of parallel teeth at an angle to the first set. Single cut files are typically used for sharpening tools and finishing operations, while the more aggressive double cut files are used for rapid material removal and rough shaping of material.
The shape of the file used should be similar to the profile of the cut being made. For example, you might use a flat file to smooth flat edges, and a round file to taper the inside edge of a drilled hole. Common file shapes include flat, triangle, half round, round, and square.
The first and most basic filing technique is called straight-filing, and involves pushing the file lengthwise across the work, making contact only on the forward stroke.
Straight-filing is typically used to rapidly remove material.
If a smooth surface is what you’re aiming for, then it’s best to use the draw-filing technique.
In draw-filing, the file is held on both ends and is pulled and pushed across the material crosswise.
Inevitably, your file will become clogged with material, and won’t work as well. One way to prevent material from sticking is to scrape a piece of chalk across the file before using it. To remove the bits of material stuck between the teeth, you can clean your file by using a tool called a file card, which you scrape across the file in the direction of the teeth.