Investigations of the incipient cutting process have mainly used ductile materials (lead/brass) at low speeds (⩽5 m/s). The present study is more realistic as it uses mild steel (0.45 percent C) at conventional speeds (50-300 m/s). High-speed films and force traces of the incipient stage were taken. Hardness profiles of the chiphead were also constructed. Two types of chip shape were found. One type occurs in the range of lower speeds (⩽150 m/s) with larger depths of cut (⩾0.30 mm/rev). Both types can be explained by the change in relative magnitudes of friction and the cutting force.

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