Drilling tool geometry: The obtuse angle included between the chisel edge and a cutting lip, as viewed from the end of a twist drill, is called what?

Introduction / Context:
Understanding twist drill nomenclature is essential for accurate hole making and tool life. Several angles define how a drill cuts: point angle, helix (rake), lip clearance (relief), and chisel edge angle. The question specifically asks for the obtuse angle formed between the chisel edge and a cutting lip, as seen from the end of the drill.

Given Data / Assumptions:

• A standard twist drill with two cutting lips and a chisel edge at the center.
• Viewpoint is the end view of the drill (looking at the point).
• Typical shop geometry values are assumed (e.g., point angle about 118°, chisel edge angle about 55°–60°).

Concept / Approach:
The chisel edge is the web portion that intersects the two lips. It does not cut effectively; instead, it extrudes material and contributes to thrust. The angle between this chisel edge and either cutting lip, measured in the end view, is known as the chisel edge angle and is obtuse by design to strengthen the web and manage thrust.

Step-by-Step Solution:

Verification / Alternative check:
Compare with known definitions: point angle is the included angle between lips (roughly 118°), helix angle is the flute spiral angle, and lip clearance is the relief behind the lip. Only the chisel edge angle fits the description asked.

Why Other Options Are Wrong:

• Helix (rake) angle: spiral of the flute, not an end-view angle between chisel edge and lip.
• Point angle: included angle between the two lips, not between chisel edge and a lip.
• Lip clearance angle: relief behind the cutting lip, measured in a different plane.

Common Pitfalls:
Confusing the point angle (between lips) with the chisel edge angle (between chisel edge and a lip). Also, assuming the chisel edge cuts; it mainly extrudes, increasing thrust.

Final Answer:
Chisel edge angle