The Relationship Between The Geometric Angle Of Twist Drill And The Sharpening Accuracy

1.apical angle

It is the angle between the projections of the two main cutting edges in the midsection. The smaller the apex angle, the longer the main cutting edge, the load on the unit cutting edge is reduced, and the axial force is decreased, which is beneficial to the axial stability of the drill bit. Moreover, the tip angle at the outer circle increases, which is conducive to heat dissipation and improving the tool durability. However, the reduction of the apex angle will weaken the drill tip strength and increase the chip deformation, resulting in an increase in torque. The apex angle of the standard twist drill is approximately 118°. HSS high-speed steel drill: The apex angle is generally 118 degrees, sometimes more than 130 degrees. HM carbide drill: The apex angle is generally 140 degrees; the straight flute drill is often 130 degrees, and the three-flute drill is generally 150 degrees.

2.relief angle

The relief angle at any point on the cutting edge is the angle between the cutting plane and the flank face at that point. The relief angle of the drill bit is not measured in the main section but in the assumed working plane (feed section). During the drilling process, it is this relief angle that actually works and is also convenient to measure. The relief angle of the drill bit is obtained by grinding. When grinding, attention should be paid to making it smaller at the outer edge (about 8° - 10°) and larger near the drill center (about 20° - 30°). The reason for such grinding is to make the relief angle adapt to the change of the rake angle of the main cutting edge, so that the wedge angles at each point are approximately equal, thereby achieving a relatively balanced sharpness, strength and durability. It can also compensate for the influence of the reduction of the actual working relief angle at each point on the cutting edge due to the axial feed movement of the drill bit. At the same time, it can also improve the working conditions of the chisel edge.

3.Main declination and end edge

The main deflection Angle of the selected point on the main cutting edge of the tilt twist drill is the Angle between the projection of the main cutting edge on the base plane of the point and the direction of drilling feed. Because of the different base plane of each point on the main cutting edge of the twist drill, the main declination Angle of each point also changes. Twist drill grinding out the top Angle 2Φ, the main declination Angle of each point is determined, the relationship between them is tan=tan Φ cos (2-2)---- the selected point of the end edge inclination, which is the main cutting edge in the end projection and the Angle between the base of the point. Due to the absolute value of each point on the cutting edge blade Angle from the outer guide linger-sometimes constantly grow bigger, so that each point on the cutting edge is the main Angle of outer edge is big, small linger-sometimes constantly.

4.The transverse edge is a cutting edge perpendicular to the axis on the end face of the twist drill. The Angle of the cutting edge includes the transverse edge bevel Angle, the transverse edge front Angle and the transverse edge back Angle.

①The Angle between the transverse edge and the main cutting edge in the end plane. It is naturally formed when sharpening the drill bit, the top Angle and the back Angle are normal standard twist drills, the larger the back Angle, the smaller the Angle. A decrease in the Angle will increase the length of the transverse edge.

②The front Angle of the cross edge is negative because the base of the cross edge is located in the tool body.