Abstract: A distance sensor is arranged to be moveable relative to a workpiece, during a machining operation this movement having a limit at a position where a finished workpiece would be within an accurate measuring range of the sensor. As machining progresses the sensor is moved towards the workpiece, stopping either when the separation of sensor and workpiece reaches a pre-set value of when the sensor reaches the limit of its movement. If the separation of sensor and workpiece reaches the pre-set value the sensor is moved away from the workpiece and then towards it again, repeating the cycle. If the sensor reaches the limit of its movement it remains in this position and measures its separation from the workpiece for the remainder of the machining operation.

Abstract: Apparatus suitable for inspecting the positional accuracy of a hole or passage in a workpiece comprising workpiece support means and a probe assembly. The probe assembly comprises two parallel tubes; one provided with a thermistor bead maintained at a temperature higher than ambient and the other provided with a nozzle adapted so as to direct a jet of air on to the thermistor bead. The tubes are positioned on each side of a workpiece to be inspected so that as the tubes are traversed across the workpiece, the jet of air is prevented from impinging upon the thermistor bead. However when a hole or passage in the workpiece is spanned by the nozzle and thermistor bead, the air jet will impinge upon the thermistor bead, thereby cooling it and hence providing a signal that a hole or passage has been encountered.