Typical cutting speed with an HSS tool when machining cast iron (average shop practice): select the closest value.

Introduction / Context:Choosing the correct cutting speed for a material–tool pair is a core machining skill. For cast iron machined with high-speed steel (HSS) tools, shops commonly use moderate speeds to balance tool life and productivity. This item checks familiarity with a representative “average” value from standard recommendations.

Given Data / Assumptions:

• Work material: common grey cast iron.
• Tool: HSS turning tool in good condition.
• Conventional dry or light coolant application; no special coatings.

Concept / Approach:Grey cast iron is free-cutting due to graphite flakes but is abrasive. HSS tools, while tougher than carbides, lose hardness at elevated temperature. Hence, typical practice uses speeds in the low-to-mid tens of m/min, depending on grade, hardness, rigidity, and coolant. A value near 22 m/min is a widely cited “average” starting point.

Step-by-Step Solution:

Verification / Alternative check:Handbook ranges may extend lower for hard CI grades or higher with excellent cooling/rigidity. A practical starting value of about 22 m/min is consistent with conservative shop practice, optimizing tool life for HSS.

Why Other Options Are Wrong:

• 10–15 m/min: very conservative; useful for difficult CI grades but below typical “average.”
• 30 m/min: possible with favorable conditions, but higher than the midrange “average.”
• 45 m/min: more appropriate for carbide tooling, not HSS.

Common Pitfalls:Using carbide speed data for HSS; ignoring diameter effects (surface speed changes with rpm and diameter); not adjusting for hardness, rigidity, or coolant presence.

Final Answer:22 m/min