If you look at the website of Crescent Tools, the parent company of file manufacturer Nicholson, and search for files, you will get 415 results. With so many options, how does one sort out which metal file is best for the job?

Files come in a variety of coarseness and types of cut. American pattern files are available in three tiers of coarseness: bastard cut, medium cut, and fine cut. The cut can be either single or double; in the latter case, the second cut comes across the first at an angle. Files from RapidCut have diamond-shaped teeth and are used primarily for coarse work. The coarseness of the cut of most files varies proportionally with the length of the file—a shorter file will be finer than a loner one. The file length is generally measured by total length of the file minus the tang. American pattern files can be anywhere between 4″ and 16″ long.

Swiss pattern files have a much larger range of cut coarseness; 00 is the coarsest, 6 is the finest, and 0 to 4 are the most available. The coarseness of these files also varies with the length of the file. These files are shorter than American pattern files, generally between 2″ and 8″ long, and are often used for fine work.

Types of Metal Files

Three flat metal files, including flat smooth, magic cut and flat file with a safe edge, as well as a triangular and barrette metal file.

Flat Files

Files come in many cross-sectional shapes, but the most basic is rectangular. A parallel-edged flat file is simply called a hand file and an American flat file is slightly tapered. Both American and hand files come in the largest variety of sizes.

Some have what is called a “safe edge”—that is, an edge with no teeth. This allows the file to cut into a corner with-out damaging the adjacent surface. It is good practice to polish the safe edge with a diamond stone or other type of stone to be certain the safe edge has no cutting capability. Grinding a safe edge is not recommended because it is likely to draw the temper, or heat-induced toughening, out of the file.

Generally, I tend to favor fine-toothed files (in American pattern, that’s either medium or fine cut) over coarse ones. They remove material nearly as quickly as the coarse ones and leave a better finish. I like to attach a file handle to all but the smallest files; this allows better control of the tool and increased comfort.

Triangular Files

Triangular files—“three square” in Swiss pattern—are used for saw sharpening as well as other situations where getting into a corner is needed. The same “safe edge” modification used on rectangular files can be implemented on triangular files. If one surface has no teeth, the tool can file cleanly into a corner. Triangular files with a safe edge are the best tool for filing a square hole.

Square Files

Square files—“four square” in Swiss pattern—are not as good as triangular files or barrette files for filing into a corner. Even with a safe edge they tend to rock somewhat and therefore do not file square.

Barrette Files

Barrette files are similar in pattern to triangular files but are flatter in section and have no teeth on the top two edges. They also come to a very sharp point. These are generally confined to Swiss pattern and therefore mostly used for detailed work, but can be very useful for getting into small spaces. A 4″-long file is a great tool for detailed finishwork; these are quite expensive. A 6″ barrette file from Grobet is over $30.

Three types of round metal files, a knife file, and a crossing file.

Round Files

Round files are just what you might think. Of these, rat-tail files are tapered, and chainsaw files are straight.

Knife Files

Knife files are V-shaped and can be useful for removing material in a narrow space.

Crossing Files

Crossing files are a rather specialized file type that are nonetheless readily available and useful in certain circumstances in which a half-round file is too round. Crossing files have a gently curved section—sometimes on only one side and sometimes on both. The term crossing comes from filing the crossings, or spokes, of clock wheels.

Multiple three inch needle files next to a metal ruler.

Needle Files

Needle files are quite small and generally come in sets of various shapes; they are useful in jobs where delicacy is required. These are often Swiss pattern and there-fore available in a good number of cuts.

Multiple two inch needle files next to a metal ruler.

The smallest needle files, available from Grobet USA, have approximately 2″ of cutting surface length and are of a very high quality. Nicholson makes larger needle files of good quality.

Assorted diamond rifflers

Rifflers

Rifflers come in more than 20 different shapes and are curved in the area of the file teeth. They can be purchased in several grades of coarseness. Smaller versions are called “die sinker” rifflers. These are well suited for work in tight spaces.

How to Use a Metal File

There are three basic filing techniques: straight filing; draw filing; and lathe, or rotary, filing.

Straight filing is done using only the push stroke. Dragging the file back over the material dulls the file just as it does a hand-plane blade. Smooth, slow strokes produce a better result than quick ones. Filing produces heat, and the faster you move the file the more heat is produced, making it more likely for the teeth to fill up with scrap material. When filing small pieces, it can be helpful to rest the piece on a flat cork block (a yoga block, for example). The stickiness of the cork helps hold the piece in place while you file.

Draw filing is done by pulling the file perpendicular to the work surface—usually by holding the file in both hands. This produces a smooth finish. Draw filing is used to prepare an edge on a scraper blade before sharpening on a stone. As with any file operation, the finer the file, the smoother the finish.

Lathe filing is used on a lathe to dress a surface. There are special files made for this purpose. This technique tends to load up the file quickly, so cleaning the file often is advisable.

When filing aluminum and other sticky materials, a bit of WD 40 sprayed on the file will help keep the material from sticking to the file teeth. You can also purchase files specifically designed for use on aluminum.

Cleaned metal file next to a ruler.

How to Clean a Metal File

I learned a technique for cleaning files from an English clockmaker. He pointed out that a file card is a brush with hardened-steel teeth, and questioned the wisdom of dragging that over a file. His technique was this: get a bar of brass about 3/4″ wide and 1⁄8″ thick and file it off square and smooth on one end. Attach a handle to make it more comfortable to use.

Brass metal file cleaning bar.

Run the bar of brass parallel to the file teeth. The soft brass will form teeth that are the same pitch as the file teeth. The formed teeth in the brass scrape the debris out of the file teeth. Once the chunks are loosened, use a brass wire brush to clean out the dust. Once the end of this shop-made cleaning tool is rounded so much that it doesn’t clean the file well, simply file it square again. This technique will remove paint and other things a file card would not touch.

 

Bart Chapin is the sole proprietor of a machine automation and design company. He has owned, repaired, built, rowed, and sailed boats from a young age.