Question

The angle between the two cutting edges of a drill bit is called:

• A. Helix angle
• B. Point angle
• C. Chisel edge angle
• D. Lip angle

Hint:

The "Point" is the business end of the drill that touches the metal first. Therefore, the angle formed by those two cutting lips right at that tip is naturally called the Point angle. For almost all standard engineering applications, remember the magic number: 118$^\circ$.

Answer 1

The Correct Option is B

1. Defining the Point Angle: The

Point angle is the angle measured between the two main cutting edges (lips) of the drill bit when viewed from the side. This angle determines how the drill centers itself and how much force is required for penetration.

2. Standard Values and Variations:

• General Purpose: For standard mild steel and general materials, the point angle is traditionally ground to

118$^\circ$.

• Hard Materials: For harder steels or manganese alloys, a flatter point angle (e.g., 135$^\circ$ to 150$^\circ$) is used to provide a stronger cutting edge.

• Soft Materials: For softer materials like wood, plastics, or soft aluminum, a more acute (sharper) point angle (e.g., 60$^\circ$ to 90$^\circ$) is often preferred to reduce tearing.

3. Clarifying Other Angles:

• Helix Angle: The angle of the flutes (the "twist") relative to the axis of the drill. It helps in chip removal.

• Chisel Edge Angle: The angle between the chisel edge and the cutting lip when looking at the end of the drill.

• Lip Angle: Also related to the clearance, this ensures that only the sharp edge touches the work and not the heel of the drill.