Twist drill helix angle vs. driving torque at a given feed For a standard twist drill (typical helix ≈ 30°), how does changing the helix angle affect the torque needed to drive the drill at the same feed? Choose the correct condition that increases the torque requirement.

Concept/Approach
The drill's helix angle affects the effective rake angle at the cutting lips and the ease of chip evacuation. A smaller helix reduces effective rake, increasing cutting resistance and the torque required.

Step-by-step reasoning
• Decrease in helix → decrease in effective rake → higher shear deformation and friction.• Chip evacuation worsens, adding to torque demand.

Verification
Conversely, a larger helix increases effective rake and eases chip flow, generally reducing torque for the same feed/material.

Final Answer
Helix angle less than 30°