Machine tool construction: The bed of a conventional engine lathe is typically made from which material?

Introduction / Context:The lathe bed must provide stiffness, damping, wear resistance, and dimensional stability. Material choice determines vibration behavior, long-term accuracy, and manufacturability of the precision guideways. This question focuses on the standard material used for lathe beds in conventional machine tools.

Given Data / Assumptions:

• Conventional cast construction with ribbed sections.
• Need for good damping and wear resistance at the guideways.
• Mass production feasibility and cost considerations.

Concept / Approach:Close-grained cast iron is traditionally used for machine tool beds because it has excellent damping capacity, good machinability, and can be surface-hardened at the guideways. Chilled cast iron refers to locally rapid-cooled surfaces (the “chill”) that produce a hard, wear-resistant skin on the sliding ways, which enhances life and accuracy retention.

Step-by-Step Solution:

Verification / Alternative check:Textbooks and builder catalogs consistently cite cast iron beds (often with chilled or induction-hardened ways) as standard. Steel beds are uncommon due to poorer damping and higher cost to achieve stability.

Why Other Options Are Wrong:

• Mild/alloy steels: stiff but poor damping; expensive to stabilize; not typical for beds.
• Pig iron: a generic term; not the finished engineering material for precision beds.
• Aluminium bronze: unsuitable for large beds; too expensive and insufficient stiffness.

Common Pitfalls:Confusing the localized hardening method (chill or induction) with the bulk bed material; overlooking the importance of damping in precision machining.

Final Answer:chilled cast iron