Controlling surface finish in single-point turning To achieve a specified average surface roughness during single-point turning on a lathe, which parameter requires the most careful control (all else being equal)?

Introduction / Context:
Surface finish in turning is strongly linked to the kinematics of the tool relative to the work surface. While many variables play a role, one factor dominates the theoretical roughness generated by a nose-radius tool in a steady-state cut.

Given Data / Assumptions:

• Single-point turning with a defined tool nose radius.
• Stable cut, no chatter, tool wear under control.
• Work and tool materials are compatible; coolant use is standard.

Concept / Approach:
The kinematic (ideal) roughness for a tool with nose radius r is commonly approximated by Ra ∝ f^2 / (8r) or related forms, showing a quadratic dependence on feed f. Cutting speed affects built-up edge and can improve finish indirectly, but the primary deterministic term is feed. Depth of cut influences cutting forces and potential chatter, but does not dominate theoretical surface texture the way feed does.

Step-by-Step Solution:
Recall roughness relation: Ra scales with f^2 for a given nose radius.To decrease Ra, reduce feed (or increase nose radius within limits).Therefore, to hit a target finish, controlling feed is the most critical lever.

Verification / Alternative check:
Machining handbooks recommend finish passes with small feeds (and adequate nose radius) to meet low Ra requirements.

Why Other Options Are Wrong:
Depth of cut mainly affects forces, not ideal roughness. Speed may reduce built-up edge but does not control the geometric roughness. Rake angle and coolant help chip flow and temperature but are secondary to feed for texture.

Common Pitfalls:
Attempting to achieve fine finish by speed alone; using a very large nose radius without sufficient rigidity can cause chatter.

Final Answer:
Feed