The geometric angle of twist drill bit:
1. Apex angle 2 Φ
It is the included angle of the projection of the two main cutting edges in the middle section. The smaller the apex angle is, the longer the main cutting edge is, the load on the unit cutting edge is reduced, and the axial force is reduced, which is strong for the axial stability of the bit. And the sharp angle of the cutter at the outer circle increases, which is conducive to heat dissipation and improve the durability of the cutter. However, the decrease of the vertex angle will weaken the strength of the drill tip and increase the chip deformation, resulting in the increase of torque. The apex angle of standard twist drill bit is about 118 degrees. HSS high speed steel bit: the top angle is generally 118 degrees, sometimes more than 130 degrees. HM cemented carbide bit: the top angle is generally 140 degrees; Straight slot drills are often 130 degrees and three edge drills are generally 150 degrees.
2. Anterior angle
It is the angle between rake face and base plane in orthogonal plane. The relationship between the rake angle of any selected point of the main cutting edge and the helix angle, main deflection angle and edge inclination is Tan = Tan / sin + tancos formula (2-3). As the helix angle gradually decreases from the outer diameter to the drill center, the edge inclination angle also gradually decreases (negative value increases). When the main deflection angle is constant, the rake angle decreases from + 30 ° to – 30 °, and the cutting conditions near the center of the drill bit are very poor.
(Please refer to passage Relationship between Geometric Angle and Precision of Twist Drill Bit Ⅱ to read the following content.)
Post time: Mar-04-2022