Correct option is D
The lip clearance angle is a critical parameter in the design of a twist drill, as it ensures efficient cutting and reduces friction between the drill and the workpiece. This angle is the angle between the flank of the drill (the surface behind the cutting edge) and a plane perpendicular to the drill's axis. For most general-purpose twist drills, the lip clearance angle typically ranges between 12 and 15 degrees.
A proper lip clearance angle is essential because:
1. It prevents the drill's flank from rubbing against the workpiece, which could cause excessive heat and wear.
2. It allows the cutting edge to penetrate the material effectively, ensuring smooth and efficient drilling.
3. It helps in chip evacuation, as the chips can flow away from the cutting zone without obstruction.
If the lip clearance angle is too small (less than 12 degrees), the drill may rub against the workpiece, leading to overheating and premature wear. On the other hand, if the angle is too large (more than 15 degrees), the cutting edge may become weak and prone to chipping or breaking.
