Understanding the File System

I'm not talking about computer file systems; I mean the files that are hardened steel tools. Selecting the proper file can be daunting with the massive range of files available and tasks they can perform, but the process becomes much simpler with a bit of information.

At their most basic, files are tools made from very hard steel with an abrasive surface cut into them. They are used to shape material and clean up rough and burred surfaces. Files are classed by two basic criteria: shape and tooth coarseness.

Tooth Coarseness
There are three primary levels of file coarseness. In order of most to least coarse, these are bastard, second cut, and smooth. A coarser file removes material much more quickly, but leaves a rougher, less finished surface. A finer tooth cut is far slower-working, but produces a finish that is smooth to the touch and looks much more polished.

Shape
The shape of the material being worked determines the best shape of file for the task.

• Mill and flat files are squared bars used for general stock removal on flat surfaces. They represent the first thing that comes to most folks' mind at the word "file." 
• Triangle files have three cutting surfaces. They show their best features on inside corners or cleaning burred threads on bolts. 
• Round or "rat tail" files look exactly like the tail of a rat, hence their name. Their shape makes them ideal for filing inside circular holes.
• Half-round files are my personal favorite; if I can only have one file, I'll pick a half-round. One face is flat like a mill file, while the other face is arched to work in rounded areas, and the faces meet at a sharp point, allowing triangle-style function.

Other File-Like Things
Needle files are very small, very fine-cut files. They remove material slower than any of the other files mentioned, but they leave wonderfully polished surfaces. I keep a set around for working on small machined parts or fitting things like firearms.

Rasps look like files, but with teeth more akin to a cheese grater. They're used for rapid removal of very soft materials like wood, plastic, and chitin (horse hooves). They remove material much faster than a normal file, and resist getting clogged with removed debris.

By Simon A. Eugster - Own work, CC BY-SA 3.0, Link

Using Files
File teeth are directional, meaning they only cut one way. They are designed to be pushed forward against the working surface. Pulling a file backward in a sawing motion will not remove any material, but can quickly dull your tool. Instead, push your file forward with even, moderate pressure. At the end of the stroke, lift the tool from the workpiece and reset it for the next stroke.


When selected and run properly, files will provide years of service, sometimes even a lifetime. Keep your axes sharp, your threads clean, and other metal projects deburred.

Lokidude