Twist drill geometry for effective cutting For a standard twist drill, should the lip clearance angle be larger at the circumference and decrease towards the center (chisel edge) to balance cutting and strength?

Introduction / Context:
The lip (relief) clearance angle on a twist drill prevents rubbing behind the cutting edge. Its distribution from periphery to center affects cutting efficiency, heat generation, and tool strength.

Given Data / Assumptions:

• Standard jobber-length twist drill geometry.
• Moderate feeds and speeds on common engineering materials.

Concept / Approach:
At the drill center, cutting speed approaches zero. Excessive relief there would weaken the web and cutting edge. Therefore, drills are ground with greater clearance at the periphery where speed is highest and rubbing risk is greater, and progressively smaller clearance towards the center to maintain strength and avoid chattering of the chisel edge.

Step-by-Step Solution:
Recognize speed distribution: v = omega * radius; near center, v ~ 0.Set relief higher at periphery to reduce rubbing at high surface speed.Reduce relief towards center to support the thin web and chisel area.Conclusion: the lip clearance angle decreases towards the center.

Verification / Alternative check:
Drill grinding charts show typical relief angles larger at the margin and smaller near the web; split-point and web-thinning geometries further optimize central cutting.

Why Other Options Are Wrong:
No (B) contradicts standard practice; (C) and (D) impose unneeded material-specific restrictions; (E) constant relief is not ideal due to varying cutting speeds across the radius.

Common Pitfalls:
Over-relieving the lips near the center causing weak chisel edge; insufficient relief at the periphery causing rubbing and heat.

Final Answer:
Yes