Surface finish in machining: What is the typical effect on surface finish when both depth of cut and feed rate are increased (other factors unchanged)?

Introduction / Context:
Surface finish is influenced by geometric factors (feed marks), material behavior, and dynamics. Increasing feed and depth of cut changes chip load and cutting forces, which generally worsens roughness unless compensated by tool geometry, coatings, speed, or rigidity enhancements.

Given Data / Assumptions:

• Same tool, nose radius, and cutting speed.
• Machine rigidity and damping unchanged.
• Homogeneous work material and stable cutting (no chatter onset considered separately).

Concept / Approach:
Geometrically, the theoretical roughness from feed marks increases with feed because scallop height is proportional to feed^2 divided by 8 * nose radius for turning. Larger depth of cut and feed also increase forces and heat, encouraging built-up edge and vibration, both of which further degrade finish.

Step-by-Step Solution:

Verification / Alternative check:
Shop trials routinely show improved finish when reducing feed and using a larger nose radius or finishing pass at small depth of cut; cutting data tables specify separate roughing and finishing feeds/depths.

Why Other Options Are Wrong:
Improvement with higher feed/depth contradicts geometry; “no effect” ignores increased scallop height; mirror-like finish requires low feed, sharp tool, and stability.

Common Pitfalls:
Trying to correct a poor finish by only increasing speed while leaving feed and depth high; overlooking machine rigidity and tool overhang.

Final Answer:
Deteriorates