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About twist drill basic point of view
- Jan 09, 2018 -

1. Helix angle β helix angle is the drill bit spiral groove on the outermost helix developed into a straight line with the bit axis angle. Because of the same lead point at each point of the spiral groove, the helix angle at different diameters of the drill bit is different. The helix angle at the outer diameter is the largest and the closer to the center, the smaller the helix angle is. Increasing the helix angle increases the rake angle, is conducive to chip removal, but the bit stiffness decreases. The twist angle of a standard twist drill is 18 ° to 38 °. For smaller diameter drill bit, the helix angle should be smaller to ensure the bit rigidity.

2 rake γOm Twist drill rake face is a spiral surface, the main cutting edge of each point of the rake angle is different. From the outer circle to the center, the anterior horn gradually decreases. The tip angle is about 30 ° at the tip and about -30 ° near the chisel edge. The rake angle on the chisel is -50 ° to -60 °.