Angle action and characteristics of standard twist drill
The main deviation angle is RM, and the main angle is the angle between the tangent of the main cutting edge and the feed direction of the m. The base surface of the twist drill is the plane at which the main cutting edge is selected, including the axis of the drill bit. The bit is not the main cutting edge through the axis line, so each point on the cutting edge of different base, the main angle points are also different. When the angle of grinding, the main angle can be determined. The main deflection angle and the vertex angle are two different concepts.
The front angle is 2, and the front angle is the projection angle of the two main cutting edges on the plane parallel to them. A small sharp angle easily cut workpiece, axial force is small, and the cutting edge length increases, cutting nominal thickness decreases, conducive to heat dissipation and improve tool life; if the front angle is too small, then the bit intensity of deformation increases, the torque is increased, the breakage of the drill bit. Therefore, a reasonable front angle should be sharpened according to the strength and hardness of the workpiece material. The front angle of the standard twist drill is 2 and phi is 118 degrees.
The back angle of the selected point on the main cutting edge of the twist angle alpha Om is expressed by the feed back angle alpha Om in the point column section. The column section is the point m of the main cutting edge, a line parallel to the axis of the drill, and the cylindrical surface formed by the rotation of the line around the center of the bit. The alpha Om changes along the main cutting edge, and the closer to the center, the greater the alpha Om. The back angle of the outer edge of the twist drill is usually 8 to 10 degrees, and the back angle of the transverse blade is 20 to 25 degrees. This can compensate for the influence of the angle of the main cutting edge on the actual working angle of the main cutting edge due to the axial feed motion of the bit, and can adapt to the change of the front angle.
Front angle gamma Om (since the front surface of the twist drill is a spiral surface, the front angles of the points on the main cutting edge are different. From the outside, the center angle decreases gradually. The rake angle at the nose point is about 30 degrees, and about -30 degrees near the cross edge. The front angle on the cross edge is -50 degrees to -60 degrees.
The helix angle, the beta helix angle, is the angle between the most outer spiral line of the drill bit spiral groove and the axis of the drill bit. Since the lead of each point in the spiral groove is the same, the helix angle of the drill bit at different diameters is different, the helix angle at the outside diameter is the largest, and the closer the central helix angle is, the smaller the helix angle is. Increasing the helix angle increases the rake angle, which is beneficial to chip removal, but the drill bit stiffness decreases. The spiral angle of a standard twist drill is 18 to 38 degrees. For smaller diameter bit, the spiral angle should be smaller to ensure the rigidity of the drill bit.
