Surface Metrology Equipment Information

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

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.