Experimental data are presented which demonstrate a strong correlation between tool wear and the signal of a thermocouple located at a position on the cutting tool remote from the cutting edge. A mathematical model is proposed for explaining this relationship between tool wear and- temperature. The model is supported by good statistical agreement between the data and the form of the proposed equation. For a total of nine different machining conditions with replications for several of the conditions, the correlation coefficient ranged in value between 0·837 and 0·978.