In precision layout and inspection, is the statement ‘‘A surface plate is used to check the trueness (flatness and straightness) of flat surfaces’’ correct with respect to the standard use of surface plates and auxiliary tools?

Introduction / Context:

A surface plate is a fundamental reference in metrology and toolroom practice. It provides an accurately lapped, flat datum on which parts are placed for inspection, layout, and measurement. Knowing what ‘‘checking trueness’’ on a surface plate entails prevents misuse and ensures reliable dimensional control on the shop floor.

Given Data / Assumptions:

• Surface plate (cast iron or granite) of appropriate grade.
• Use with straightedges, feeler gauges, dial indicators, height gauges, and scribers.
• Task: evaluate flatness, straightness, and squareness features relative to a datum.

Concept / Approach:

By providing a stable, flat datum surface, a surface plate enables checks for trueness of flat surfaces via auxiliary instruments: e.g., blueing with a reference straightedge, sweeping with a dial indicator on a height gauge, or performing light-band tests for highly finished optics. The plate itself does not measure; it supports and references accurate measurements and comparisons.

Step-by-Step Solution:

Verification / Alternative check:

Calibration certificates for surface plates specify flatness (e.g., μm over the plate size); in use, the plate facilitates repeatable, traceable inspections for flatness and straightness.

Why Other Options Are Wrong:

• False: contradicts standard practice.
• Only with CMM: CMMs are optional; manual methods suffice.
• Only for rough surfaces: plates are more suited to precision, not roughness measurement.
• Grade-0 requirement: different grades exist; suitability depends on tolerance, not a single grade.

Common Pitfalls:

• Relying on the plate without clean conditions—dust or burrs invalidate readings.
• Using damaged or out-of-calibration plates, leading to false conclusions.

Final Answer:

True