Drill having construction for reducing thrust load in drilling operation, and method of manufacturing the drill

A drill which is to be rotated about an axis thereof in a predetermined rotating direction, for drilling a hole in a workpiece, comprising:

• flutes each extending from an axially distal end portion of said drill toward an axially proximal end portion of said drill;
• and
• margins each of which is located on a rear side of a corresponding one of said flutes and extends along a corresponding one of said flutes,
• wherein each of said margins has a non-relief surface which intersects the corresponding one of said flutes to provide a leading edge, and a relief surface which is located on a rear side of said non-relief surface as viewed in said predetermined rotating direction,
• wherein said non-relief surface has a width of 0.1-0.5 mm as measured in a circumferential direction of said cylindrical body portion,
• and wherein a radial distance of said non-relief surface from said axis is substantially constant as viewed in said predetermined rotating direction, while a radial distance of said relief portion from said axis is gradually reduced as viewed in said predetermined rotating direction.

A drill which is to be rotated about an axis thereof in a predetermined rotating direction, for drilling a hole in a workpiece, comprising:

• a cylindrical body portion having:
• primary cutting edges and secondary cutting edges formed in an axially distal end portion thereof such that each of said secondary cutting edges is located on a radially inner side of a corresponding one of said primary cutting edges;
• flutes each of which extends from said axially distal end portion toward an axially proximal end portion thereof;
• distal end flank surfaces each of which is located on a rear side of a corresponding one of said primary cutting edges and a corresponding one of said secondary cutting edges as viewed in said predetermined rotating direction, and each of which has a clearance angle that permits an axial distance between each of said flank surfaces and said axially proximal end portion to be reduced as viewed in said predetermined rotating direction;
• inclined surfaces each of which is located on a rear side of a corresponding one of said flank surfaces as viewed in said predetermined rotating direction, and has a clearance angle larger than that of the corresponding one of said flank surfaces;
• primary rake surfaces each of which defines a corresponding one of said primary cutting edges;
• and
• secondary rake surfaces each of which defines a corresponding one of said secondary cutting edges, such that each of said secondary rake surfaces is located on a radially inner side of a corresponding one of said primary rake surfaces;
• wherein each of said secondary rake surfaces and the corresponding one of said primary rake surfaces are provided by an axially distal end portion of a rear side wall, as viewed in said predetermined rotating direction, of a corresponding one of said flutes,
• wherein each of said secondary rake surfaces is recessed in such a direction that permits a web thickness in said axially distal end portion to be reduced,
• wherein each of said inclined surfaces extends from a corresponding one of said secondary rake surfaces to a periphery of said cylindrical body portion, and is inclined such that an axial distance between each of said inclined surfaces and said axially proximal end portion is reduced as viewed in a direction substantially perpendicular to a corresponding one of said secondary cutting edges, from the corresponding one of said secondary rake surfaces toward said periphery of said cylindrical body portion,
• and wherein each of said inclined surfaces and the corresponding one of said secondary rake surfaces are connected to each other without a step therebetween.

A method of manufacturing a drill which is to be rotated about an axis thereof in a predetermined rotating direction for drilling a hole in a workpiece, and which comprises a shank portion and a cylindrical body portion contiguous to each other, wherein said cylindrical body portion includes:

• (a) primary cutting edges and secondary cutting edges formed in an axially distal end portion thereof such that each of said secondary cutting edges is located on a radially inner side of a corresponding one of said primary cutting edges;
• (b) primary rake surfaces of said primary cutting edges and secondary rake surfaces of said secondary cutting edges;
• and (c) inclined surfaces each of which extends from a corresponding one of said secondary rake surfaces to a periphery of said cylindrical body portion, and is inclined such that an axial distance between each of said inclined surfaces and said shank portion is reduced as viewed in a direction substantially perpendicular to a corresponding one of said secondary cutting edges, from the corresponding one of said secondary rake surfaces toward said periphery of said cylindrical body portion, said method comprising:
• a step of forming each of said inclined surfaces by an outer circumferential surface of a grinding wheel, while at the same time forming the corresponding one of said secondary rake surfaces by an axial end surface of said grinding wheel which intersects said outer circumferential surface of said grinding wheel at a predetermined angle.