The phenomenon of ‘stick-slip’ oscillations of the feed drives of machine tools is an important problem in the design of certain types of machine tools. The factors contributing to this particular type of instability are studied both experimentally and analytically with the aid of a simple model based on dynamic measurements. The experimental work is restricted to a scraped cast iron-cup ground cast iron slideway interface. The principal experimental variables are lubricant viscosity and the natural frequency of the drive. The dynamic observations provide evidence and data that enable the use of a simple model rather than the more usual application of an involved analysis. The consideration of analytical and experimental results allows further understanding of the mechanism of feed drive instability to be developed.