Turning and other metal cutting: When the primary objective is superior surface finish, which parameter strategy is generally preferred?

Introduction / Context:
Surface finish results from tool geometry, feed, speed, nose radius, and machine-tool rigidity. For a given setup, specific choices of feed and cutting speed reliably produce smoother surfaces. This question probes the classic parameter trade-off when finish is prioritized over productivity.

Given Data / Assumptions:

• Stable machine-tool-fixture conditions with adequate rigidity.
• Appropriate nose radius and sharp tool.
• Work material amenable to conventional finishing parameters.

Concept / Approach:
Surface roughness in turning is strongly influenced by feed per revolution (geometry-controlled roughness) and to a lesser extent by cutting speed (which can reduce built-up edge and improve chip formation). Lower feed reduces cusp height, while higher cutting speed reduces BUE and tearing, improving finish.

Step-by-Step Solution:

Verification / Alternative check:
Simple geometric relation shows arithmetic roughness proportional to (feed^2)/(8*R) for nose radius R; lowering feed directly lowers roughness. Empirically, higher speeds produce cleaner shearing for many steels and aluminums.

Why Other Options Are Wrong:

• High MRR implies higher feed/depth, worsening finish.
• Dry machining may be fine in some cases but is not the finish-driving parameter.
• Soft tools blunt quickly and harm finish.
• High feed/low speed worsens roughness and may promote BUE.

Common Pitfalls:
Ignoring chatter from inadequate rigidity; even optimal parameters cannot compensate for vibration or worn tools.

Final Answer:
Low feed and high cutting speed