Tech Talk
What causes "Regenerative Chatter" in a grinder?
As with the surface grinding machines described previously, cylindrical grinding machines are designed with high rigidity and dynamic stability. The concentricity of the ground workpiece depends largely on the quality of the headstock and the method by which the workpiece is held. In weaker systems, where the machine may be poorly designed or the part holding system is inadequate, regenerative chatter can occur.
Regenerative chatter is a vibration due to the cyclic variation in the grinding wheel depth of cut, initiated by a machine vibration which occurs at a natural frequency of the machining system. Once the grinding wheel/workpiece system begins to vibrate at a resonant frequency, the grinding wheel and workpiece will cycle radially towards and away from one another. The motion creates a wave pattern around the workpiece which corresponds to the frequency of the vibration. The wave pattern on the workpiece, caused by the originating vibration, produces cyclic forces on the system.
The cyclic forces occur at the critical frequency initiated by the varying depth of cut of the grinding wheel as it encounters the crests and the valleys of the wave pattern. Once regenerative chatter has begun, it is very difficult to eliminate. The machining parametres must be changed. The wheel speed and work speed should be changed and the in-feed decreased. The grinding wheel should also be dressed.
