Twist drill geometry: What is the usual (standard) helix angle of a general-purpose twist drill?

Introduction / Context:
The helix angle of a twist drill affects chip evacuation, cutting forces, and guidance. General-purpose drills are designed with a compromise angle to suit a wide range of materials and machine conditions. This question asks for the commonly used standard value.

Given Data / Assumptions:

• Uncoated HSS drill for general workshop use.
• No special aluminum or stainless-specific geometry.
• Standard point angle around 118° assumed.

Concept / Approach:
General-purpose twist drills typically use a helix angle near 30°. Lower helix (~20–25°) favors harder materials with short chips, while higher helix (~35–45°) is chosen for aluminum and ductile materials to aid chip evacuation. The standard compromise for broad applicability remains about 30°.

Step-by-Step Solution:

Verification / Alternative check:
Catalogs from major drill manufacturers list “general-purpose” series with helix close to 30°, with variants for aluminum (higher helix) and hard steels (lower helix).

Why Other Options Are Wrong:
20° or 45° are specialized ranges; 60° is not used as a helix angle for twist drills; 12° is far below practical values for chip transport in drills.

Common Pitfalls:
Confusing helix angle with point angle; assuming one helix fits all materials without considering chip evacuation needs.

Final Answer:
30°