Abstract: A system for monitoring the vibration of a power driven cutting tool during machining first produces a signal proportional to the vibration spectrum of the tool over a preselected band width. This is passed through a digitally controlled attenuator which is adjusted to provide an output signal at a preselected level. The degree of attenuation is stored, as is a reference value which is generated as a function of the attenuated signal. Then, during subsequent machining operations under the same machining conditions the attenuator is controlled to provide the same degree of attenuation and the reference value, which is in the form of a digital signal, is compared with the rectified and digitized output of the attenuator. When the latter exceeds the reference value a control signal is generated which either provides an audible or visual warning that the cutting tool is worn and therefore due for replacement or initiates an automatic tool changing operation.

Abstract: The invention describes a method of machining a workpiece with a cutting l arrangement involving relative rectilinear movement between workpiece and tool, a heat source being mounted for transverse movement in a series of arcuate passes across the workpiece to heat and soften the portion thereof immediately ahead of the cutting tool. In examples given, the heat source is one or two plasma torches and the arcuate passes are part of an oscillatory or of a rotational movement.