What is chatter?
The onset of chatter during machining is primarily a function of the variation in chip thickness that occurs due to vibration of the tool, workpiece, or both. This situation is shown schematically in Fig. 1. In this figure, the flexible tool engages the workpiece and, due to the cutting force, begins vibrating. This vibration is imprinted on the machined surface. In milling, the next tooth on the rotating cutter overcuts this wavy surface produced by the previous tooth. This wavy surface varies the instantaneous chip thickness which, in turn, modulates the cutting force and the cutter vibration (i.e., a feedback mechanism is produced that can lead to self-excited vibrations, or chatter). Depending on the relationship between the wavy surface left by the previous tooth and the current cutter vibration, the resulting deflections and forces can grow very large (chatter) or diminish (stable cutting). An example of a stable turning operation is shown in Fig. 2, where the tool vibrations are
