A method of machining a screw is provided that is capable of preventing formation of a protruding section at a thread tip section. A thread is formed by cutting on a cylindrical body, and a surface of the thread is plastically deformed by rolling. Because of the cutting, a width between-side surfaces of a thread tip section is in a narrowed state as compared to a normal width. This width is narrowed toward a tip of the thread while a thread body section has a width expanded as compared to a normal width. Consequently, the side surfaces are formed to bulge by an excess thickness portion as compared to normal side surfaces. The rolling plastically deforms both side surfaces to cause the excess thickness portion to plastically flow toward the side surfaces.

A method of machining a screw is provided that is capable of preventing formation of a protruding section at a thread tip section. A thread is formed by cutting on a cylindrical body, and a surface of the thread is plastically deformed by rolling. Because of the cutting, a width between-side surfaces of a thread tip section is in a narrowed state as compared to a normal width. This width is narrowed toward a tip of the thread while a thread body section has a width expanded as compared to a normal width. Consequently, the side surfaces are formed to bulge by an excess thickness portion as compared to normal side surfaces. The rolling plastically deforms both side surfaces to cause the excess thickness portion to plastically flow toward the side surfaces.

A drill bit has, along a drill bit axis, a drilling head, a multi-start helix made of two or more helical coils, and an insertion end. The helix has a helix slope and a pitch in a delivery region. In an outlet region of the helix, the outlet region being directed towards the insertion end, the helical coils merge continuously, within a first portion, from an orientation in alignment with the helix slope into an orientation parallel to the drill bit axis. A length of the first portion is at least one quarter of the pitch of the delivery region. The helical coils, in a second portion, are oriented parallel to the drill bit axis.

A drill bit has, along a drill bit axis, a drilling head, a multi-start helix made of two or more helical coils, and an insertion end. The helix has a helix slope and a pitch in a delivery region. In an outlet region of the helix, the outlet region being directed towards the insertion end, the helical coils merge continuously, within a first portion, from an orientation in alignment with the helix slope into an orientation parallel to the drill bit axis. A length of the first portion is at least one quarter of the pitch of the delivery region. The helical coils, in a second portion, are oriented parallel to the drill bit axis.

A method of machining a screw is provided that is capable of preventing formation of a protruding section at a thread tip section. A thread is formed by cutting on a cylindrical body, and a surface of the thread is plastically deformed by rolling. Because of the cutting, a width between-side surfaces of a thread tip section is in a narrowed state as compared to a normal width. This width is narrowed toward a tip of the thread while a thread body section has a width expanded as compared to a normal width. Consequently, the side surfaces are formed to bulge by an excess thickness portion as compared to normal side surfaces. The rolling plastically deforms both side surfaces to cause the excess thickness portion to plastically flow toward the side surfaces.