ROUNDNESS FORMING CUTTER AND ROUNDNESS FORMING METHOD

PROBLEM TO BE SOLVED: To provide a roundness forming cutter, by which cutter positioning precision can be eased while an application ratio of NC machining can be improved, and to reduce the number of work setting so as to improve workability. SOLUTION: In a roundness forming cutter 10, a round blade 11 which is recessed toward the outside and is provided with a center angle of less than 90 degrees is formed in the tip circumferential face part in a rotary knife main body, while straight blades 12, 13 are formed on the both side tangential line extensions of the round blade 11. In addition, along the extension line of the straight blade 13 on the tip side, the second round blade 14 protruded to the outside is formed, while on the end face of the rotary knife main body, a bottom blade 15 leading to the round blade 14 is formed.