A mold machining method using an endmill, the contour of a cross section of the mold being concave and continuous in an area, a ratio of the maximum to the minimum of radius of curvature of the contour of a portion of the area (a first area) being 2 or greater, and a blade of the endmill having a second area where the contour of a cross section is similar to the contour of the first area, the method comprising the steps of determining a spiral path of the endmill such that each point of the first area is machined by a portion of the second area, corresponding to said each point in the similarity, and a radial interval between the spiral tool path is maximized while keeping surface roughness of the machined mold at or below a predetermined value; and machining the mold along the path.

A mold machining method using an endmill, the contour of a cross section of the mold being concave and continuous in an area, a ratio of the maximum to the minimum of radius of curvature of the contour of a portion of the area (a first area) being 2 or greater, and a blade of the endmill having a second area where the contour of a cross section is similar to the contour of the first area, the method comprising the steps of: determining a spiral path of the endmill such that each point of the first area is machined by a portion of the second area, corresponding to said each point in the similarity, and a radial interval between the spiral tool path is maximized while keeping surface roughness of the machined mold at or below a predetermined value; and machining the mold along the path.

A hole is formed in an elbow through the steps of: forming a starting hole in a material, the starting hole having an undercut remaining on a hole surface; finishing an inner diameter of the starting hole (11.sub.-3) on one end side by revolving a side cutter (II) including an arc-shaped cutting edge and having an outer diameter smaller than a finishing hole diameter while rotating the side cutter (II) in such a posture that the side cutter (II) is inclined in a predetermined direction relative to the material (12), the revolving being carried out so that the side cutter moves along a hole surface to be finished; and finishing the inner diameter of the starting hole (11.sub.-3) on another end side by revolving the side cutter (II) while rotating the side cutter (II).

A chamfering tool that chamfers an opening edge of a target hole formed in a work, the chamfering tool including a support shaft, a base shaft having the support shaft on a tip end side thereof and being eccentric with respect to the support shaft, and a blade portion having a rake face that is a step surface of a step protrusion portion protruded laterally from the support shaft or that is an end surface of the support shaft. The blade portion including an edge line in a shape of a curve and being bulged to a side away from a center axis of the support shaft, and the edge line being inclined with respect to an axial direction of the support shaft.

A chamfering tool that chamfers an opening edge of a target hole formed in a work, the chamfering tool including a support shaft, a base shaft having the support shaft on a tip end side thereof and being eccentric with respect to the support shaft, and a blade portion having a rake face that is a step surface of a step protrusion portion protruded laterally from the support shaft or that is an end surface of the support shaft. The blade portion including an edge line in a shape of a curve and being bulged to a side away from a center axis of the support shaft, and the edge line being inclined with respect to an axial direction of the support shaft.

The present invention provides a tool body (20) for use in an indexable rotary cutting tool, the tool body (20) having a rotational axis and a substantially cylindrical shape. Spiral grooves (28) are formed so as to extend from a base end side of the tool body to a leading end side in a peripheral surface (23) of the tool body. The spiral grooves (28) each have a plurality of insert seats (30) formed so as to be shifted from each other from the base end side toward the leading end side. The insert seats (30) each have a bottom surface (31) and first and second side surfaces (32, 33) that extend so as to intersect with the bottom surface (31). The first side surface (32) faces the base end side of the tool body (20), and the second side surface (33) faces the leading end side of the tool body (20) and is located on the base end side with respect to the first side surface (32). In at least one insert seat (30) located closer to the base end side with respect to an insert seat (30) located closest to the leading end side of the tool body (20), a length (L1) of the first side surface (32) is longer than a length (L2) of the second side surface (33).

A cylindrical tool body has a peripheral surface provided with one or more spiral grooves extending from a base end side to a leading end side. The grooves each have a plurality of insert seats which are shifted relative to one another from the base end side toward the leading end side. The insert seats each have a bottom surface, a first side surface of length L1, and a second side surface of length L2. The first side surface faces the tool body's base end side, and the second side surface faces the tool body's leading end side and is located on the base end side with respect to the first side surface. In at least one insert seat located closer to the base end side than an insert seat located closest to the tool body's leading end side, the first side surface is longer than the second side surface.