A drill structure comprises a shank part and a bit part. A web is formed on the front end of the bit part. Two sides of the web are tilted backward to form two cutting faces. At least one flute (chip-discharge groove) is formed on the surface of the bit part. Each cutting face includes a primary cutting face and a secondary cutting face. The thickness of the prismatic web edge of at least one primary cutting face is smaller than the outer-side width of the primary cutting face. An auxiliary cutting face is extended to the wall of the flute from the cutting edge of the primary cutting face and a portion of a blade back of the secondary cutting face of another cutting face. The present invention decreases the drilling resistance during drilling a hole and increases the service life of the drill bit.

A cutting tool 1 includes a cutting edge equipped with a helically curved groove 2 at a side outer periphery in the longitudinal direction, and a coolant passage pipe 3 extended internally and communicatively connected with ejection holes 4 of coolant arranged inside the groove 2 by way of a coolant passage pipe 31 branched from the coolant passage pipe 3 extended around a rotation center axis along the longitudinal direction or along the helically curved groove.

A drill includes a drill body having a longitudinal axis, a front end, and a frontend portion and at least one flute in the front end portion. A cutting insert is mounted to the drill body in each flute of the at least one flute at the front end of the drill body. The at least one flute includes a plurality of grooves, concave surfaces of adjacent ones of the grooves intersecting to define a ridge separating the grooves.

A rotary cutting tool with an elongate body disposed about a longitudinal axis, the elongate body including a helical flute and a polycrystalline-diamond cutting tip. The cutting tip comprises an inner portion having an inner point angle and an outer portion having an outer point angle different from the inner point angle.

In an embodiment, a drill has an elongated shape and a rotation axis. The drill includes a drilling portion, a shank portion, and a tapered portion. The shank portion includes a first helical flute and a first cutting edge. The tapered portion is located between the drilling portion and the shank portion. The tapered portion includes a second helical flute, a second cutting edge, a chamfered part, and a connection part. The chamfered part is getting smaller gradually as moving toward the first end side. The connection part has a curved surface and connects the second cutting edge and the drilling portion. A ratio of w/L is 0.0015-0.5 where L is a length of the second cutting edge in a front view of the first end, and w is a width of an outer peripheral end of the chamfered part in a direction parallel to the rotation axis.

The present disclosure provides a multi-groove pagoda drill bit. A circumferential wall of a tapered body is provided with a diameter-expanding step increasing in diameter from front to back. A plurality of primary helical grooves extending from a rear end to a front end and a plurality of secondary helical grooves extending from the rear end to close to the front end are opened on the circumferential wall of the tapered body. An axial cutting blade same as a cutting trajectory is disposed on groove mouths of the primary helical grooves and the secondary helical grooves. On a radial section of the tapered body, a front recess segment located at a side of a line connecting an edge tip and an axis and close to the edge tip is disposed in the groove mouths of the primary helical grooves and the secondary helical grooves.

A drill according to an embodiment of the present invention has a pair of main cutting edges positioned at a front end of a drill body, a pair of first chisel edges each extending from the pair of main cutting edges toward a rotation axis, and a second chisel edge positioned between the pair of first chisel edges and intersecting with the rotation axis of the drill body. When viewing a locus of rotation of the pair of first chisel edges and a locus of rotation of the second chisel edge in a cross section taken so as to include the rotation axis, the respective locus of rotation of the pair of first chisel edges have a rectilinear shape, and respective imaginary straight lines obtained by extending the locus of rotation of the pair of first chisel edges toward the rotation axis are positioned further to a rear end side of the drill body than the locus of rotation of the second chisel edge.

A drill structure comprises a shank part and a flute part disposed on one end of the shank part. The front region of the flute part has a web. Two sides of the web are tilted backward to form a first cutting face and a second cutting face. At least one flute is formed on the outer surface of the flute part. The flute part has a bit core in the center thereof. The radius of the cross section of the bit core is defined as the web thickness. The first cutting face includes a first primary cutting face and a first secondary cutting face. The second cutting face includes a second primary cutting face and a second secondary cutting face. The first cutting edge of the first primary cutting face is not parallel with the first connection edge. The width of the primary cutting face width is larger than the web thickness. The drill structure has high cutting ability and long service life.

A drill of the present invention includes: a drill main body; a plurality of convex-arc cutting edges which are formed on a tip side of the drill main body from an outer periphery of the drill main body to a chisel edge provided near to a rotational axis; second faces which are each formed in an approximately band shape and are each formed along each of the convex-arc cutting edges on a back side of the convex-arc cutting edge in the rotational direction; third faces which are each formed to be continuous with a back side of each of the second faces in the rotational direction; and fourth faces which are each formed to be continuous with a back side of each of the third faces in the rotational direction.

A method for producing a twist drill has the following steps. A blank is shaped to form a semi-finished product. The semi-finished product is formed from a core, coaxial with the drill axis, having a radius and a number of webs, arranged on the core, having a height. The semi-finished product has a constant cross section along the drill axis. The webs have a first portion which adjoins the core and in which a width of the web remains constant or decreases in the circumferential direction with increasing radial distance from the drill axis. The webs have a second portion which adjoins the first portion and in which the width of the web increases in the circumferential direction with increasing radial distance from the drill axis. The webs of the semi-finished product are shaped into helical segments using a plurality of rolling tools that annularly enclose the semi-finished product and roll on the webs along the drill axis. The rolling tools have teeth that are inclined with respect to the drill axis. A height of the helical segments is less than the height the webs. Helical segments formed from adjacent webs are in contact with one another in a closing fold. The invention also relates to a twist drill.