Surface metrology equipment is used to measure the surface finish and/or geometry of engineering components. Surface texture and topology characteristics that can be identified include roughness, contour, form, waviness, and defects.

Types of Surface Metrology Equipment

There are two main types of surface metrology equipment: form gages and surface profilometers.

• Form gages, form gaging systems, and contour measuring machines are used to inspect parameters such as roundness, angularity, squareness, straightness, flatness, runout, taper, and concentricity.
• Surface profilometers measure roughness, waviness, and other finish or surface texture parameters by either contact or non-contact methods.

a. Contact or stylus-based instruments drag a sharp, pointed tool across the surface. Height variations of the tip are recorded and then used to form a texture profile of the surface. Most contact or stylus-based surface metrology equipment provides a two-dimensional (2D) or line profile.

b. Non-contact instruments measure surface texture by optically scanning the surface with a light or laser. Optical or light-based profilometers can also use triangulation or interferometry to measure or capture a surface profile. Non-contact devices can provide three-dimensional (3D) or areal-topography measurements.  

Measurement Capabilities

Surface metrology equipment differs in terms of measurement capabilities. Form gages and surface profilometers can measure a variety of parameters in addition to 2D or 3D measurements.

• Coaxiality is a measure ofone axis to another axis.
• Cylindricity is a condition of a surface of revolution in which all points on the surface are equidistant from a common axis.
• Taper is a narrowing or differential variation in diameter along the axial or length dimension of a cylindrical part.
• Flatness places all of the points on a part's surface within a single plane.
• Eccentricity is a ratio which describes the shape of a conic section.Concentricity is twice the eccentricity.
• Harmonic content orshape variationsare repeated undulations which occurin a 360° rotation. Most surface metrology equipment describes harmonic frequencies in undulations per revolution (UPR).

Measurement capabilities for surface metrology equipment may include a number of different characteristics.

• Lay is a surface texture with a predominant directional pattern due to machining, grinding, or other processing.
• Parallelism describes the equidistance between two planes or surfaces.
• Roundness is measured using the minimum radius separation (MRS), least-squares center (LSC), or minimum inscribed circle (MIC) methods.
• Runout is measured by determining the radial difference between two concentric reference circles drawn to just enclose the profile of the part or cylindrical surface under evaluation.
• Roughness profiles are the finer scale surface variations that remain after form and waviness variations have been filtered out of the raw profile.
• Squareness or perpendicularity is a measure of variation of the part's surface from a 90° angle to the reference surface.
• Spacing parameters measurethe horizontal or lateral peak-and- valley variations ofa profile along the surface.

Other measurements that may be made include angularity, step height, straightness, thickness, waviness, warp, and bow.