How to File Metal

Metal files are relatively inexpensive and effective tools for reshaping and smoothing metal and hard plastics, offering the potential for high precision and many years of trouble-free use.

This article covers the common techniques of cross filing and draw filing, as well as maintenance.

1. Procure the workpiece, plan the operation, and layout lines indicating where material is to be removed. It is important to make sure that the material to be filed is softer than the file - so do not try to file hardened steel with a (hardened steel) file; you will quickly ruin it. In a similar way, diamond-embedded files should not be used on soft materials, including many softer steels, as this will cause the diamonds to be torn out.
   
   
2. Select a file that is best for the job. Their are many types of files, coming in various sizes, shapes, degrees of coarseness, and tooth geometries.
   
   
3. Clean the file. There should not be any pins (bits of filed metal) stuck in the teeth; if there are, clean them out with a stiff wire brush or, if necessary, a piece of skinny wire or sheet metal. Also lard or oil can be used to lubricate the file and make cutting easier because of the loss of friction from metal rubbing against metal and to remove the chance of having pins form and stick in the teeth. The lard/oil will also keep the metal dust down making cleanup and breathing in the given area where a lot of filework is done much easier. Another benefit to using lard/oil is the rust protection on the piece and the file itself. Just remember that there is oil or lard on the piece if you need to do work that requires the surface to be clean of it.
   
   
4. Chalk/oil/lard the file: liberally rub chalk into the teeth of the file or a small amount of lard/oil. This makes the file less likely to become clogged with pins in the future.
   
   
5. Clamp the work in the vice. It should protrude far enough that you are not likely to rub the file on the hardened steel jaws of the vice, but not any more than this - if the work extends too far from the jaws of the file, it will vibrate ("chatter") during the filing, making the work take longer and the finish of the work poor.
   
   
6. Now, for the actual filing, we diverge (the following 3 steps are not to be taken in order - you may indeed only do one of them):
   • For heavy cross filing, to remove material, grab the handle of the file with the dominant hand and place the palm of the other hand on the end of the file. Orienting the file so that it points away from you, press down firmly (so that the file digs in and cuts the metal) and make long, slow strokes away from your body, removing downward pressure on the return stroke to prevent dulling the file.
     
     
   • For light cross filing, to remove material with a small file (as for detail work), grab the handle of the file with the dominant hand and place the fingers of the other hand on the end of the file. Orienting the file so that it points away from you, press down firmly (so that the file digs in and cuts the metal) and make long, slow strokes away from your body, removing downward pressure on the return stroke to prevent dulling the file.
     
     
   • For draw filing, to make a highly finished surface, grab each side of the file with your hands only somewhat further apart than your workpiece. Orienting the file so that it points to your side, press down firmly (so that the file digs in and cuts the metal) and make long, slow strokes away from your body, removing downward pressure on the return stroke to prevent dulling the file.
     
     

• The file cleaning and chalking step may be repeated as necessary to ensure a good surface finish by keeping the file clean of pins.
• If filing cast iron, be sure to knock the scale off first! It is very hard and will quickly ruin a file.