The author presents some of the results of a series of tests in which the principal phase of study concerned the temperature developed at the contacting surface of the tool and the chip. This tool-chip interface temperature is referred to as the “cutting” temperature. The determination of the tool-chip interface temperature was by means of the Herbert-Gottwein tool-work thermocouple wherein the steel workpiece constituted one member of a thermo-couple and the cemented-carbide insert the other member. This principle has been used in the study of cutting temperatures, the investigation of friction between unlike metals, the study of surface temperatures of brass wire drawn through steel dies and for investigation of surface temperatures of mating gears of unlike metals.