INTRODUCTION Much more interest in machinability investigations has been shown in recent years, both by colleges and by Industrial Research departments, due partly to the difficulty encountered in machining some of the new gas turbine materials and partly to the availability of simple and economical dynamometers as are described in this Note. These dynamometers were designed to provide simple robust instruments capable of being easily applied to a wide range of machines without modification. Direct mechanical movement is the basis of their construction and this has been justified by the trouble free service given over a period of five years. Almost onehundred of each of these instruments are being used, and so many requests have been received for a more comprehensive account of their range of uses that the preparation of this Note seemed justified. It is encouraging to see the vigour displayed by industry and the Colleges in this field since so much remains to be done to establish practical machinability, data for British materials. By collaboration between investigators it should be possible to arrange a programme of research to cover a wide range of materials with the minimum duplication. The illustrations of the instruments are shown by the courtesy of Coventry Grinders Ltd. , Coventry.