The circular-saw blades in this experiment were divided into an even number of sector areas with equal center angles. Alternate areas on the blade were hammered on both sides by a hammer with an elliptical peen whose longer axis was in the radial or tangential direction. This type of hammering is called partial hammering. Slots with equal lengths also were cut at equal intervals from the bottom of the gullets towards the center of the blade. In such circular-saw blades with partial hammering and slots, critical rotation speeds and natural frequencies were obtained experimentally. The lateral vibration during sawing also was observed. With partial hammering, the critical rotation speed is increased. By partial hammering or slots, some vibration modes split into two modes, and natural frequencies of these split modes are a little different from each other. In one of these modes, nodes are situated at all middle positions of non-hammered areas or at all slot positions, and in another mode, anti-nodes are situated at the same positions. The difference between the natural frequencies of mc,des split by partial hammering or slots is greater than the difference by uniform hammerings. When the differences of the natural frequencies between split modes are sufficiently large, the occurrence of lateral vibration at the resonant rotation speed when an exciting frequency due to sawing coincides with a natural frequency of a forward traveling wave, can be suppressed effectively.
