A study of orthogonal cutting mechanisms has been conducted using a system concept. The cutting process is considered as taking place within the cutting system, which is defined as consisting of the following components: the cutting tool, the chip and the workpiece. The term `system' emphasizes that an overall operation process, within a frame of the system time, is under consideration rather than a collection of pieces. Using the introduced concept, the chip-formation process in the cutting of brittle and elasto-plastic workpiece materials is considered as a result of the dynamic interactions of the systems components. The system consideration reveals that: (i) the formation of the chip is caused by the bending stress when it is combined with the shear stress in the deformation zone; and (ii) the chip formation process is cyclical. Sample calculation and results of experiments are used to illustrate the existence, role and significance of the bending stress.