Machinery's Handbook, 31st Edition
810 Surface Texture such factors as machine or work deflections, vibration, chatter, heat treatment, or warping strains. Roughness may be considered as being superposed on a ‘wavy’ surface. Definitions of Terms Relating to the Measurement of Surface Texture.— Terms re- garding surface texture pertain to the geometric irregularities of surfaces and include roughness, waviness and lay. Profile is the contour of the surface in a plane measured normal, or perpendicular, to the Height (z) is considered to be those measurements of the profile in a direction normal, or perpendicular, to the nominal profile. For digital instruments, the profile Z(x) is approxi mated by a set of digitized values. Height parameters are expressed in micrometers (μm). Height range (z) is the maximum peak-to-valley surface height that can be detected accurately with the instrument. It is measurement normal, or perpendicular, to the nominal profile and is another key specification. Mean line (M) is the line about which deviations are measured and is parallel to the general direction of the profile within the limits of the sampling length. See Fig. 2. The mean line may be determined in one of two ways. The filtered mean line is the centerline established by the selected cutoff and its associated circuitry in an electronic roughness average measuring instrument. The least squares mean line is formed by the nominal profile, but by dividing into selected lengths the sum of the squares of the deviations minimizes the deviation from the nominal form. The form of the nominal profile could be a curve or a straight line. Peak is the point of maximum height on that portion of a profile that lies above the mean line and between two intersections of the profile with the mean line. surface, unless another angle is specified. Graphical centerline. See Mean Line. Profile measured is a representation of the real profile obtained by instrumental or other means. When the measured profile is a graphical representation, it will usually be distorted through the use of different vertical and horizontal magnifications but shall otherwise be as faithful to the profile as technically possible. Profile, modified is the measured profile where filter mechanisms (including the instru ment datum) are used to minimize certain surface texture characteristics and emphasize others. Instrument users apply profile modifications typically to differentiate surface roughness from surface waviness. Profile, nominal is the profile of the nominal surface; it is the intended profile (exclusive of any intended roughness profile). Profile is usually drawn in an x-z coordinate system. See Fig. 2.
Measure Profile
Z
X
Nominal Profile
Fig. 2. Nominal and Measured Profiles
Profile, real is the profile of the real surface. Profile, total is the measured profile where the heights and spacing may be amplified differently, but otherwise no filtering takes place. Roughness profile is obtained by filtering out the longer wavelengths characteristic of waviness. Roughness spacing is the average spacing between adjacent peaks of the measured pro file within the roughness sampling length.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online