Drill and drill grinding method and apparatus

A drill having an axis of rotation comprising a pair of symmetrically arranged cutting edges formed at one end of a shank, said shank having an outer periphery, each of said cutting edges having a flank followed by a land with a first land portion and a second land portion on opposite sides of a demarcation line and further followed by a discharge flute when viewed from said one end of said shank, each of said cutting edges comprising a central edge portion extending from said axis of rotation and an outer edge portion, said central edge portion being formed with a central face substantially parallel to the axis of the drill, said first land portion of one of said cutting edges extending from said flank in a direction opposite the direction of rotation of said drill to said demarcation line, said second land portion having an outer end section extending from said outer periphery of said shank and an inner end section extending from said axis of rotation, said inner end section extending from said demarcation line to the central face of the central edge portion of the other symmetrical cutting edge, said first land portion and said second land portion being intersected by a phantom cutting plane which ext ends parallel to said axis of the drill and which extends substantially perpendicularly through an intermediate part of said central edge portion, said cutting plane intersecting said second land portion at a first line of intersection, said first line of intersection being disposed at a first angle relative to said central face, said cutting plane intersecting said first land portion at a second line of intersection, said second line of intersection when continued by a phantom line to said central face being disposed at a second angle relative to said central face, said second angle being greater than said first angle.

A method of improving the cutting ability of a drill having an axis of rotation by providing central cutting edge portions of the drill with high strength while providing for smooth discharge of chips, said drill being of the type having symmetrically arranged cutting edges at one end of a shank having an outer periphery and with each of said cutting edges having a flank followed by a land with a first land portion and a second land portion on opposite sides of a demarcation line and further followed by a discharge flute when viewed from the direction of feed of the drill, each of said cutting edges also having a central edge portion ext ending from said axis of rotation and an outer edge portion and wherein the central edge portions are each formed with a central face substantially parallel to the axis of the drill, the steps of forming a second land portion at the trailing end portion of the land of one cutting edge with said second land portion having an outer end section extending from said outer periphery of said shank and an inner end section extending from said axis of rotation and further with said second land portion extending to the central face of the central edge portion of the other symmetrical cutting edge and thereby providing an increased area to said central face and improving the cutting ability of the drill while providing the central cutting edge portion with high strength and enhanced chip discharge capability, said step of forming said second land portion thereby dividing said land into two portions disposed on opposite sides of a demarcation line, one of said two land portions being designated a first land portion, the other of said two land portions being said second land portion, said first land portion and said second land portion being intersected by a phantom cutting plane which extends parallel to said axis of the drill and which extends substantially perpendicularly through an intermediate part of said central edge portion, said cutting plane intersecting said second land portion at a first line of intersection, said first line of intersection being disposed at a first angle relative to said central face, said cutting plane intersecting said first land portion at a second line of intersection, said second line of intersection when continued by phantom line to said central face being disposed at a second angle relative to said central face, said second angle being greater than said first angle.

A drill having an axis of rotation, an outer peripheral surface, and a drill tip, comprising a pair of symmetrically arranged cutting edges formed at one end of a shank, each of said cutting edges having a flank followed by a land means, said land means having a first land portion and a second land portion on opposite sides of a demarcation line, said demarcation line being a straight line extending from the axis of said drill to said peripheral surface, each of said cutting edges comprising a central edge portion extending from said axis of rotation and an outer edge portion each extending substantially straight and being joined to each other with an obtuse angle formed therebetween when seen from the direction of feed of the drill, said central edge portion being formed with a central flat face substantially parallel to the axis of the drill, the central edge portion of one cutting edge being disposed at an 180.degree. angle with respect to the central edge portion of the other cutting edge, said first land portion of one of said cutting edges extending from said flank in a direction opposite the direction of rotation of said drill to said demarcation line, said second land portion extending from said demarcation line to the central face of the central edge portion of the other symmetrical cutting edge, said second land portion forming a substantially partial conical surface having its vertex disposed at the center of said drill tip, a phantom cutting plane extending parallel to the axis of the drill and extending substantially perpendicularly through an intermediate part of said central edge portion, said first land portion and said second land portion being intersected by said phantom cutting plane, said phantom cutting plane intersecting said second land portion at a first line of intersection, said first line of intersection being disposed at a first angle relative to said central face, said cutting plane intersecting said first land portion at a second line of intersection, said second line of intersection when continued by a phantom line to said central face being disposed at a second angle relative to said central face, said second angle being greater than said first angle, whereby said central edge portions of said cutting edges having enhanced strength while providing for enhanced chip discharge.