Turning practice: What is the typical average cutting speed range for turning mild steel using a high-speed steel (HSS) single-point tool?

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:

  • Work material: mild steel (low carbon steel).
  • Tool material: HSS single-point tool.
  • Objective: typical average cutting speed range, not the extreme ends.
  • Normal dry or lightly lubricated conditions, conventional lathe.


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:

Identify tool material limitations: HSS requires relatively low speeds.Identify work material: mild steel is not abrasive but still generates heat.Use common ranges from handbooks: about 25–30 m/min for general turning with HSS.Select the listed option that brackets this range.


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:

  • 15 to 19 m/min: overly conservative for routine mild steel turning.
  • 60 to 90 m/min and 90 to 120 m/min: typical of carbide or better tool materials, not HSS.


Common Pitfalls:
Confusing HSS recommendations with carbide; ignoring coolant and rigidity effects can also mislead selection.



Final Answer:
25 to 31 m/min

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