The cutting force is the most important variable by means of which to understand the mechanics of ultra-precision machining. However. most tool dynamometers monitor the static cutting force, although it is necessary to measure the dynamic cutting force to clarify the machinability of the material, the formation of the chip, chatter and the wear of the tool, In this research, a combined-type tool dynamometer which can measure the static cutting force and the dynamic cutting force together by use of strain gauges and a piezo-film accelerometer has been developed. An analysis of the dynamometer has also been carried out. (C) 1997 Elsevier Science S.A.