Abstract The knowledge of the friction mechanism and hence the distribution of the normal and shear stresses at the chip-tool interface in metal cutting is far from complete. Following the few previous attempts in the literature, the possibility that the boundary layer theory can be invoked to describe the chip flow process at the interface is further investigated. In this paper sticking and sliding friction regions are assumed to exist and the boundary conditions are formulated such that use is made of the boundary layer on a partially mobile solid surface and the flow lines of the chip material in the secondary shear zone are developed. These lines compare well with those obtained by known experimental techniques particularly for the case of large negative rake angle cutting.