An insert according to an embodiment includes an upper surface including a corner part, a lower surface, a side surface, and a cutting edge. The cutting edge includes a first cutting edge located at the corner part, a second cutting edge adjacent to the first cutting edge, a third cutting edge adjacent to the second cutting edge, and a fourth cutting edge adjacent to the third cutting edge. Each of the third cutting edge and the fourth cutting edge has a concave curvilinear shape extending downward in a side view. A radius of curvature of the fourth cutting edge is smaller than a radius of curvature of the third cutting edge.

A drill body of an indexable insert drill includes at least two chip flutes separated from each other in the circumferential direction of the drill body by intermediate ribs, each chip flute and each rib extending in a helically curved path. An insert seat is located at a transition between each chip flute and a front face of the drill body. Coolant ducts are arranged in and extending along a respective one of the ribs. Each coolant duct extends in a helically curved path and has an upstream end with an inlet opening and a downstream end with an outlet opening. Each coolant duct has a cross-sectional area that varies in the axial direction of the coolant duct, such that it has a smaller cross-sectional area at its outlet opening than at its inlet opening.

A straight line along the second line segment and a straight line along the fourth line segment form an acute angle. The straight line along the second line segment and the straight line along the third line segment form an obtuse angle. The straight line along the first line segment and the straight line along the fourth line segment form an obtuse angle. Each of the third curved portion and the fourth curved portion is larger in radius of curvature than the first curved portion and larger in radius of curvature than the second curved portion. In a direction perpendicular to the bottom surface, a distance between the top surface and the bottom surface is equal to a distance between the cutting edge and the bottom surface, or is shorter than the distance between the cutting edge and the bottom surface.

A drill includes a front and rear end, a shaft extending axially rearwardly from the front end, at least one cutting insert releasably mounted at the front end, a first and second chip flute in an envelope surface of the shaft, a coolant chamber inside a shank, and a first and second coolant channel extending from the front end of the coolant chamber and terminating at the drill front end. The first coolant channel is associated with the first chip flute and the second coolant channel is associated with the second chip flute. The coolant chamber includes a flow control element movable in response to a flow restriction between a neutral position, in which coolant flow is distributed substantially equally to the first and second coolant channels, and an active position, in which the flow control element directs the coolant flow at least mainly to one of the coolant channels.

An indexable drill insert includes a drill body having a central longitudinal rotational axis (C.sub.L), the drill body comprising a shank portion and a fluted cutting portion, the fluted cutting portion having a front clearance face and a plurality of flutes, the fluted cutting portion includes a central insert pocket capable of receiving a central cutting insert and a peripheral insert pocket capable of receiving a peripheral cutting insert. For the central cutting insert, a central, longitudinal axis of a projection of the flute coolant exit aperture can intersect a vertical plane (PA1) having an area (A1) or a horizontal plane (PB1) having an area (A2). For the peripheral cutting insert, the central, longitudinal axis of the projection can intersect a vertical plane (PA2) having an area (A3) or a horizontal plane (PB2) having an area (A4).

When viewed along a central axis, a start point phase of a first discharge flute falls within a range of not less than +10 and not more than +90 with respect to a central edge, an end point phase of the first discharge flute falls within a range of not less than 40 and not more than 0 with respect to the central edge, a start point phase of a second discharge flute falls within a range of not less than +10 and not more than +90 with respect to an outer peripheral edge, and an end point phase of the second discharge flute falls within a range of not less than 40 and not more than 0 with respect to the outer peripheral edge. The first discharge flute includes a first front flute portion, and a first rear flute portion contiguous to the first front flute portion.