3. Posterior angle
The back angle of any point of the cutting edge is the included angle between the cutting plane and the back face of the point. The back angle of a bit is not measured in the main section, but in the assumed working plane (feed section). In the process of drilling, this back angle actually works, and it is also convenient to measure.
The back angle of the drill bit is obtained by grinding. During grinding, pay attention to make the outer edge of the drill bit smaller (about 8 ° ~ 10 °) and larger near the drill center (about 20 ° ~ 30 °). The reason for this grinding is that it can adapt the back angle to the change of the front angle of the main cutting edge, make the wedge angle of each point roughly equal, so as to achieve the relative balance of sharpness, strength and durability, make up for the impact of the reduction of the actual working back angle of each point on the blade due to the axial feed movement of the drill bit, and improve the working conditions of the transverse edge at the same time.
4. Principal deflection angle and end edge inclination angle
The main deflection angle of the main cutting edge of the twist drill bit is the angle between the main cutting edge projection and the feed direction of drilling on the base plane of the twist drill bit. Because the base planes of the main cutting edges of the twist drill are different, the main declination of each point will also change. After twist drill bit drill out top 2 Φ, the principal deflection angle of each point is determined, and the relationship between them is Tan = tan Φ Cos formula (2-2) — the inclination of the end face edge of the selected point, which is the included angle between the projection of the main cutting edge in the end face and the basal plane of the point.
As the absolute value of the edge inclination of each point on the cutting edge gradually increases from the outer edge to the drill center, the main deflection angle of each point on the cutting edge is also large at the outer edge and small at the drill center.
(Please refer to passage Relationship between Geometric Angle and Precision of Twist Drill Bit Ⅰto read the former content Relationship between Geometric Angle and Precision of Twist Drill Bit Ⅲ to read the following content.)
Post time: Mar-13-2022