⒈The selection of the cross-sectional shape of the file

The cross-sectional shape of the file should be selected according to the shape of the filed part, so that the two shapes are compatible. When filing the inner arc surface, you should choose a semicircle file or a round file (small diameter workpiece); when filing the inner corner surface, you should choose a triangle file; when filing the inner right-angle surface, you can choose a flat file or a square file. When using a flat file to file an inner right-angled surface, pay attention to make the narrow surface (smooth edge) of the file without teeth close to one of the inner right-angled surfaces, so as not to damage the right-angled surface.

⒉The choice of file tooth thickness

The thickness of the teeth of the file should be selected according to the size of the machining allowance, the machining accuracy, and the nature of the material. Coarse-tooth files are suitable for processing workpieces with large allowance, low dimensional accuracy, large geometric tolerances, large surface roughness values, and soft materials; otherwise, fine-tooth files should be selected. When in use, it should be selected according to the required machining allowance, dimensional accuracy and surface roughness of the workpiece.

⒊ Selection of file size specifications

The size of the file should be selected according to the size of the workpiece to be processed and the machining allowance. When the processing size is large and the margin is large, the file of large size should be used, and the file of small size should be used on the contrary.

⒋The selection of file tooth pattern

The tooth pattern of the file should be selected according to the nature of the material being filed. When filing soft materials such as aluminum, copper, mild steel, etc., it is best to use a single-tooth (milling tooth) file. The single-tooth file has a large rake angle, a small wedge angle, a large chip pocket, a chip that is not easy to block, and a sharp cutting edge.