Discrete frequency noise from free running circular saws

Abstract Carbide-tipped saws of certain types emit a harsh whistling noise while running without cutting, and this noise may be so loud as to restrict working speeds. For several saws, this noise was analysed over the whole range of practical running speeds. Each sound frequency was associated with a particular mode of vibration of the saw blade. These modes and their frequencies were established from sand patterns obtained by exciting the rim of the stationary saw while it was clamped horizontally. Vibration in a rotating saw is evidently excited by flow of air past the moving teeth. This flow was investigated by testing models in a water channel. Modifications of tooth shape were tried out with a view to preventing excitation, and thus eliminating discrete noise.