For harder materials, the helix angle of the drill is:

Explanation:

The helix angle is the angle between the leading edge of the land and the axis of the drill. Sometimes it is also called a spiral angle.

1. The helix results in a positive cutting rake. This angle is equivalent to the back rake angle of a single-point cutting tool.
2. The usual range of helix angle used in the drill is 20° to 35°.
3. Large helix angle 45° to 60° suitable for deep holes and softer work materials.
4. The small helix angle of less than 45° is suitable for harder and stronger materials.
5. Zero helix angles are used in spade drills for high production drilling, micro‐drilling, and hard work materials.

Important Points

1. An increase in helix angle is given for more quick removal of chips but a decrease in helix angle will give greater strength of cutting edges.
2. The larger the value of helix angle lesser will be the power required in drilling.