The cross-sectional shape of the file should be selected according to the shape of the parts to be filed, so that the shapes of the two can be adapted. When filing the inner cambered surface, choose semi-circular file or circular file (small diameter workpiece); When filing the inner corner surface, choose a triangular file; When filing the inner right angle surface, you can choose a flat file or a square file. When selecting the inner right angle face of flat file, pay attention to make the narrow face (smooth edge) of the file toothless close to the side of the inner right angle face so as not to hurt the right angle face.

3. Selection of file tooth thickness

The thickness of the file tooth should be selected according to the allowance size, machining accuracy and material properties of the machined workpiece. Coarse tooth file is suitable for workpieces with large machining allowance, low dimensional accuracy, large form and position tolerance, large surface roughness and soft materials. Instead, choose a fine tooth file. When used, it should be selected according to the machining allowance, dimensional accuracy and surface roughness required by the workpiece.

3. Selection of file size and specification

The size and specification of the file should be selected according to the size and machining allowance of the workpiece to be machined. When the machining size is large and the allowance is large, the file with large size should be selected, otherwise, the file with small size should be selected.

4. Selection of file tooth pattern

The file tooth pattern should be selected according to the properties of the workpiece material to be filed. When filing soft materials such as aluminum, copper and low carbon steel, it is best to choose a single tooth pattern (milling tooth) file. Single-tooth file has the advantages of large rake angle, small wedge angle, large chip groove, difficult chip blocking and sharp cutting edge.