In a previous study of orthogonal machining of CA 360 brass, periodic load fluctuations were related to geometric features observed on the machining chip. In this study, the metallography of these machining chips was examined using both optical and scanning electron microscopy with the goal of better understanding the cutting mechanism and the origin of the load fluctuations. It was determined that the load variations were associated with periodic variations in chip thickness, implying a periodic variation in shear angle. It is difficult to detect such a variation in shear angle using an etch to identify deformation patterns, but shear angle variations could be inferred from the chip morphology and from the distortion of the lead particles in the machining chip. A simple model is presented which exhibits periodic shear angle variations if deformation is assumed to occur in a shear zone of finite thickness and if the material’s workhardening capacity is exhausted at strains comparable with those developed during machining. Computations incorporating the features of this model are shown to accurately reproduce the pattern of the experimental observations.

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