Tips to Select and Maintain Your Files
Files are one of the most ancient tools that you’ll find in a machine shop. They have been around for thousands of years, allegedly since the Stone Age, and they have been used by metalworkers and woodworkers to smooth, hone, clean and deburr all kinds of materials.
In modern machine shops, machinists often use files to deburr sharp edges of freshly machined parts. Understanding the different characteristics of files and how different shapes and cuts can help achieve the desired results is crucial when it comes to file selection.
As you can see in the image below, files are made up of several different sections.
The tang is usually softened to allow the handle to be screwed to it. Some files have built-in handles molded over the tang.
The face, or belly, is where the cutting action happens. Some files have more than two faces and feature different tooth patterns.
Similarly, the edges of a file can be smooth or have teeth. Smooth edges are also called safe edges. Depending on its shape or profile, a file can have flat edges, tapered edges or round edges.
Considerations when buying a new file
Type & Length
Files come in a variety of types and lengths. The combination of the cross-sectional shape and the contours is what defines the file type, while the length is the distance between the base of the heel and the point. Sections can be rectangular, square, circular, triangular or irregular. The contours can be parallel (aka blunt files) or tapered.
Dozens of different types exist, manufactured for both generic and specific applications. To get a better idea of how many different file types exist, you can take a look at this chart. The most commonly used type, generally called American Flat File, has a rectangular cross-section and tapered contours like this.
The cut of a file refers to the set of teeth present on the face of the tool. A single-cut file, like this, has a single set of parallel, diagonal rows of teeth. A double-cut file, like this, has two sets of diagonal rows of teeth. The second set of teeth is cut in the opposite diagonal direction, and on top of the first set. The first set of teeth is known as the overcut, while the second is called the upcut. The upcut is finer than the overcut.
Single-cut files are primarily used for soft materials and for fine work. Double-cut files, on the other hand, are used preferably when dealing with harder materials, like steel or brass, or for roughing work. Some more versatile models, like below, are single-cut on one face and double-cut on the other.
Although single-cut and double-cut are the most common type of cuts in machine shops, some files are manufactured with irregular patterns of teeth. Here are some examples:
- Rasp-cut files have a series of individual teeth that are formed by a single-pointed tool. They are used mainly on wood, hooves, aluminum, and lead.
- Mill tooth files have curved teeth individually milled on the face. They are good for soft materials.
The coarseness of a file is defined by the number of teeth per inch length of the file.
Most hand files are classified as Swiss Pattern or American Pattern.
American Pattern files are available in three grades of cut (or coarseness): Bastard, Second Cut and Smooth.
Swiss Pattern files, on the other hand, are available in seven cuts, ranging in coarseness from ØØ to No. 6, with No. 6 being the finest cut. These files are smaller and finer than American Pattern files. With teeth that extend to the edge and narrow points for working in tight areas, Swiss Pattern files are ideal for detailed work and are often used by tool and die makers.
Files you should have in your shop
Due to the broad variety of file types that are available, machine shops tend to have multiple files in their tooling racks. Although the selection of your file will ultimately depend on the type of work you will have to perform, it is generally recommended to have at least a set of all-purpose files.
This set by Nicholson contains 9 American Pattern files that will cover most of your roughing needs.
If you are a tool and die maker you will also be most likely required to own Swiss Pattern files for your precision work. This 12-piece set is a good place to start.
How to maintain a file
One of the most important aspects of file maintenance is storage. Since they work better when they are sharp, the first thing to avoid is stacking them on top of each other. This is because the friction between them can lead to dullness. Also, since you’ll probably have multiple files, it can make it difficult to find the type you need.
The best way to store files is to hang them on a rack or keep them in a drawer separated by wooden dividers. When this is not possible, we recommend keeping them in their sleeves or finding another way to keep them separated.
Since files are used to remove material from parts, it’s not unusual to see chips stuck in between the teeth. This phenomenon is called pinning and it’s one of the main causes of uneven surface finish. Luckily, there are a few remedies that can help you reduce pinning, such as brushing a little bit of oil onto the file face or rubbing chalk onto the teeth. The best way to make sure that the face of your file is clear from chips is by using a file card or a file brush (they are often combined).
By following these few simple steps, you can make sure that your file will last a long time and stay at top level performance.
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