Relief (clearance) angle for soft materials In machining soft materials, is it correct practice to use a tool with a negative relief (clearance) angle?

Introduction / Context:
The relief (clearance) angle prevents the tool flank from rubbing the freshly cut surface. Its selection depends on work material and tool material, affecting heat, wear, and surface integrity.

Given Data / Assumptions:

• Soft, ductile materials (e.g., aluminum, copper, plastics).
• Conventional single-point tools or drills.

Concept / Approach:
A negative relief angle would cause the flank to press against the work, dramatically increasing friction and heat, leading to rubbing, built-up edge, and poor finish. For soft materials, positive rake and adequate positive relief are preferred to reduce cutting forces and avoid smearing.

Step-by-Step Solution:
Recognize that relief angle must be positive for clearance.For soft materials, use larger positive rake and suitable positive relief to minimize rubbing and adhesion.Therefore, the statement that negative relief is used is incorrect.

Verification / Alternative check:
Tool geometry charts show relief angles typically 6–12° (or higher for very soft materials); negative relief is reserved for special cases on hard/brittle materials with negative rake, not negative relief.

Why Other Options Are Wrong:

• Limiting to specific alloys or inserts does not justify negative relief; modern carbides sometimes use negative rake, but relief remains positive.
• High cutting speeds do not change the need for flank clearance.

Common Pitfalls:
Confusing rake (which can be negative for strength) with relief (which must remain positive to avoid rubbing).

Final Answer:
Incorrect