Abstract: A drill includes a tip-forming front end having at least two straight cutting edges and at least two chip flutes extending from the tip end towards a rear end. Each cutting edge includes an inner portion disposed near a center line of the drill, and an outer portion disposed farther from the center line. The peripheral end of each cutting edge is in the form of a smoothly curved nose portion protruding radially with respect to the center line. The nose portion is formed by several circular segments having mutually different radii (R1, R2, R3). Adjacent ones of the radii are of different size.

Abstract: A drill comprising a tip-forming end including at least two cutting edges (8, 8′) and at least two chip flutes (7, 7′) extending from the tip end (2) towards the second end (3), having the purpose of forming and removing chips from the corresponding cutting edge. In accordance with the invention the drill tip is composed of cutting edges on mutual sides of the axial centre line having a straight unbroken contour, the central portions of which extend axially beyond the peripheral portions whilst the nose radiused surface on each cutting edge at the periphery is provided with a smoothly curved radius comprising one or several circular segments with mutually different radii (R1, R2, R3) where adjacent radii always appear with different size.

Abstract: A cutting insert for a during includes a broken main cutting edge, the ends of which join respective additional edges of the insert by curved nose portions. Each curved nose portion forms a curved cutting edge defined by at least three sequentially arranged curved cutting edge segments defined by respective radii of different sizes. A first of the segments joins one end of the main cutting edge and has a first radius. The next segment has a radius of different length than the first radius and projects farther laterally than the first segment to perform a wiping function.