Drill

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body;
• cutting members having cutting edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion, wherein said converging portion is configured so that the rate of reduction in the radius is progressively increased along said axis toward the front end of said bit body;
• and
• said substantially disk-shaped flange has a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body;
• said chip-discharging flutes having an inner surface which has (a) a first inner surface portion which is directed in the direction of rotation of said drill, (b) a second inner surface portion which is directed in the counter direction at an inclination with respect to said first inner surface portion, and (c) a third inner surface portion interconnecting said first and second inner surface portions and recessed from said first and second inner surface portion;
• cutting members having cutting edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion, the diameter of which progressively decreases along said axis towards the front end of said bit body;
• said substantially disk-shaped flange having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and so as to extend rearward therefrom along and at both sides of an axis of said bit body;
• said flutes being spirally twisted about said axis;
• cutting members having edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a converging portion, the diameter of which progressively decreases along said axis towards the front end of said bit body;
• said flange portion including a substantially disk-shaped flange connected to said converging portion and having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface;
• and
• cutting oil passage bores formed in lands defined between said chip-discharging flutes at a front end portion of said bit body, said cutting oil passage bores extending linearly at an inclination with respect to said axis in accordance with the twist of said chip-discharging flutes.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body;
• said chip-discharging flutes having a first inner surface portion which is directed in the direction of rotation of said drill, a second inner surface portion which is directed in the counter direction at an inclination with respect to said first inner surface portion, and a third inner surface portion interconnecting said first and second inner surface portions and recessed from said first and second inner surface portions, and wherein angles of intersection between said first and third inner surface portions and between said second and third inner surface portions are obtuse;
• cutting members having edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion having a diameter that progressively decreases along said axis towards the front end of said bit body;
• said substantially disk-shaped flange having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body;
• said chip-discharging flutes having an inner surface which includes:
• (a) a first inner surface portion which is directed in the direction of rotation of said drill, (b) a second inner surface portion which is directed in a counter direction at an inclination with respect to said first inner surface portion, and (c) a third inner surface portion interconnecting said first and second inner surface portions and recessed from said first and second inner surface portions, wherein said inner surface has a substantially arcuate cross section when taken along a plane perpendicular to said axis;
• cutting members having edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion having a diameter that progressively decreases along said axis towards the front end of said bit body;
• said substantially disk-shaped flange having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes helically twisted about an axis of said body and formed in the outer peripheral surface of said body opening in the front end surface of said bit body and extending rearward therefrom along and at both sides of an axis of said bit body;
• said chip-discharging flutes being twisted not greater than 9O.degree. over the entire length of said chip-discharging flutes;
• cutting members having edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion which is configured so that the rate of reduction in the radius is progressively increased along said axis toward the front end of said bit body;
• said substantially disk-shaped flange having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface.

A drill, comprising:

• a substantially cylindrical bit body;
• a pair of chip discharging flutes helically twisted about an axis of said body and formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body;
• cutting members having edge portions constituting a bottom cutting edge;
• said bit body having a flange portion which includes a substantially disk-shaped flange connected to a converging portion which is configured so that the rate of reduction in the radius is progressively increased along said axis toward the front end of said bit body;
• said substantially disk-shaped flange having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface;
• and
• inner surface portions of said chip-discharging flutes extending near a front end of said flange portion.

A drill, comprising:

• a substantially cylindrical bit body, a pair of chip discharging flutes formed in the outer peripheral surface of said body so as to open in the front end surface of said bit body and to extend rearward therefrom along and at both sides of an axis of said bit body, and cutting members having the same cutting edge portions constituting a bottom cutting edge, said bit body having a flange portion which includes a converging portion the diameter of which progressively decreases along said axis towards the front end of said bit body and a substantially disk-shaped flange connected to said converging portion and having a rearwardly facing annular end surface, said annular end surface being formed to contact a front end surface of a drill holding portion of a machine which rotatably holds said bit body substantially over the entire area of said annular end surface, wherein cutting oil discharge openings are formed in a front end surface of said bit body in regions near a trailing edge of the openings of said chip-discharge flutes as viewed in the direction of rotation of said drill, wherein recesses are formed in the front end surface of said bit body so as to extend along said trailing edges of said openings of said chip-discharging flutes and so as to be recessed axially rearwardly in communication with said chip-discharging flutes, said cutting oil discharge openings being opened in the bottoms of said recesses.