Difficulty: Easy
Correct Answer: 25 to 31 m/min
Explanation:
Introduction / Context:
Choosing a proper cutting speed in turning is fundamental for tool life, surface finish, and productivity. For mild steel turned with a high-speed steel (HSS) tool, recommended speeds are modest because HSS loses hot hardness at elevated temperatures. This question checks recall of standard shop-floor values and the reasoning behind them.
Given Data / Assumptions:
Concept / Approach:
Cutting speed must balance reasonable metal removal with acceptable tool life. HSS tools retain hardness up to a lower temperature than carbide or ceramics; therefore, their recommended speeds are lower. Practical shop tables and the Taylor tool life relationship support speeds in the few tens of metres per minute for mild steel with HSS.
Step-by-Step Solution:
Verification / Alternative check:
Applying Taylor’s tool life notion qualitatively: raising speed sharply reduces tool life for HSS, confirming that high values such as 60–90 m/min or greater are usually reserved for carbide or coated tools.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing HSS recommendations with carbide; ignoring coolant and rigidity effects can also mislead selection.
Final Answer:
25 to 31 m/min
Discussion & Comments