Patent ID: 8052355

Claim:
A processing method for processing a processed member having an opening portion with a curved inner surface by a cutting tool which includes a shank member and a processing member having a smaller diameter than the shank member, the processing method comprising: a first process for forming a through hole at the processed member by a groove portion of the processing member, the through hole extending from a surface of the processed member to reach the opening portion, the groove portion having a cutting edge which is positioned at a tip of the groove portion and a chip evacuation groove which is positioned at an outer surface of the groove portion and through which chip generated in the processing is expelled outward; and a second process which is successively performed after the first process to process a part of the inner surface of the opening portion corresponding to the through hole by the groove portion in a state where a self guide portion of the processing member is guided by the through hole, the self guide portion being provided between the groove portion and the shank member of the cutting tool and having a substantially cylindrical shape to guide the cutting edge toward the part of the inner surface of the opening portion corresponding to the through hole.