The type of file you use depends on the number of teeth on the saw.
image by Hugh Nelson/Flickr.com
A properly sharpened handsaw ensures fast, easier cuts with less risk of damage from the saw hopping on the initial cut. Sharpening an antique handsaw can help make an old, previously unusable tool work like new. Depending on the type of saw and the number of teeth per inch (TPI), different sized files might be needed. However, one size file can be used with a number of different saw configurations. In general, three or four triangular files should be sufficient for sharpening most saws.
Place the saw in a saw-sharpening vise. A saw-sharpening vise must be long enough to support the entire blade and prevent it from flexing during sharpening.
Select a file appropriate to the saw type and the number of teeth per inch on the saw. In most cases, a slim taper triangular file is the best file. Smaller files are better for saws with a higher density of teeth.
Place the triangular file between the first two teeth and make three or four draws in the file's cutting direction. Move the file to the next set of teeth and make three or four draws in the file's cutting direction. Use the same number of draws on each set of teeth.
Turn the saw around after finishing all of the teeth on the first side of the saw. Follow the same process to sharpen the teeth on the other side of the saw. This ensures a well-balanced cut on all of the saw teeth.