The correct angle of clearance exists at the drill point when which condition holds?

• A. Both lips are the same length and angle
• B. Lips are different lengths
• C. Margins are worn
• D. Drill is new

Answer: (A)

Angle of clearance at the drill point comes from the relief given to the lips of a twist drill. For that relief to exist evenly, the two lips must be identical in length and angle. When both lips are the same length and have the same angle, the relief is symmetric, keeping the flank surfaces away from the workpiece and the cutting edges free to slice cleanly. If the lips differ in length, one side has more relief than the other, causing rubbing, uneven wear, and poor hole quality because the clearance angle isn’t consistent. Worn margins or other changes can alter the effective clearance, but the decisive factor for having the proper angle at the point is having both lips identical in length and angle.