A resonant work performing apparatus is disclosed which includes a resonant system which is vibratory in resonance at an unloaded resonant frequency. The resonant system has a vibratory input at a frequency near the resonant frequency, and a vibratory output responsive to vibrations at the input. The resonant system has at least one intermediate node, and the apparatus includes a frame attached to the resonant system substantially at the node. A vibrational force is applied to the input of the resonant system at a given frequency near the unloaded resonant frequency to excite the resonant system to at least near resonance. A sensor is used to determine the frequency of the resonant system. Application of the vibrational force is controlled responsively to the sensor to hold the applied vibrational force at the given frequency.