Prediction of regenerative machine tool chatter requires a knowledge of the cutting forces existing under vibration conditions. Previous direct experimental work has been very limited in its range and has given results which contradicted those derived from observations on regenerative chatter.

A description of suitable experimental rigs and the results obtained from these rigs are given. The results show that there are large phase changes of cutting force relative to chip thickness when vibrating. A simplified criterion is given for assessing machining stability and it is shown that the observed phase changes will greatly affect machining stability; in some cases machining will be stable regardless of machine damping.

The requirements for machining stability contradict those for long cutting tool life so a compromise must be reached in practical cases.

The cutting process is not, in general, amenable to quantitative analysis but theories have been put forward to explain the observed force phase and amplitude changes. There is a reasonable qualitative correlation between experiment and theory for most of the experimental range.

Temperature estimates involved in phase change estimates show that there are large tool temperature variations under chatter or milling conditions. These temperature variations and the consequent thermal stresses are likely to cause tool failure with brittle materials such as carbides.

The results obtained under steady cutting conditions such as lathe turning have been extended to intermittent cuts as encountered in milling. The tests show that there is no fundamental difference between steady and intermittent cuts.

Suggestions are put forward for the large amount of further work required to clarify the mechanisms of the outing process and to extend cutting force knowledge for chatter prevention.