ASME B / ANSI/ASME B – Surface Texture and Gaging for Screw Threads Package ASME B and ANSI/ASME B The ASME B46 1 ANSI ASME. Find the most up-to-date version of ANSI B at Engineering The American Standard for Surface Texture in ANSI B gives Ra as the standard surface finish designation. In most applications where RMS is called.

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They are defined as the height difference between the highest and lowest pixel in the image. All six parameters are defined from the surface bearing area ratio curve shown in the figures below. This parameter is only meaningful if there is a ani direction on the sample. The Reduced Summit Height, Spkis the height of the upper left triangle.

As there are no pixels outside the borders of the image there are no local minimums or local maximums on the borders. The Ansk WavelengthSrwis the dominating wavelength found in the radial spectrum. The advantage of this is that deviations from the bearing plane can be quantified better when setting the bearing plane to zero see how this is ansu in the Plane Correction Dialog section.

The radial spectrum is calculated by the following formula:. The Ten Point Height, S10 zis defined as the average height of the five highest local b4.61 plus the average height of the five lowest local minimums:. The Roughness Average, S ais defined as:. For a Gaussian height distribution S ci approaches 1. The amplitude sum, A aat a line with the angle, ais defined as:.

Maximum Valley Depth Sv: The Area Root Mean Square Slope, S dq6is similar to the Sdq but includes more neighbor pixels in the calculation of the slope for each ajsi.

For all surfaces S vi is between 0 and 0. Parameters associated with the two-dimensional DIN standard are also calculated andi on the bearing area ratio curve. The Dominating Radial Wavelength, Srwcorresponds to the semicircle with radius, r maxhaving the highest amplitude sum, b max: All the parameters are based on two-dimensional standards that are extended to three dimensions.

Three parameters are calculated based on this figure.

Mean HeightS mean anxi the mathematical mean height of all pixels. Surfaces with very dominant directions will have Stdi values close to zero and if the amplitude sum of all direction are similar, Stdi is close to 1. Maximum Peak Height Sp: Note, also that roughness values depends strongly on measurement conditions especially scan range and sample density.

The functional parameters for characterizing bearing and wnsi retention properties are described by six parameters.

## ANSI-ASME B46.1-1985.pdf

The reported fractal dimension is the average for all directions. The Fractal Dimension, Sfd is calculated for the different angles by analyzing the Fourier amplitude spectrum; for different angles the amplitude Fourier profile is extracted and the logarithm of the frequency and amplitude coordinates calculated.

The fractal dimension can also be evaluated from 2D Fourier spectra by application of the Log Log function. The result is called the angular spectrum. The angular spectrum is calculated by the following formula:. The surface bearing area ratio curve, which is also called the Abbott curve, is calculated by accumulation of the height distribution histogram and subsequent inversion.

When there are less than five valid maximums or five valid minimums, the parameter is not defined. For an anisotropic surface the correlation length is xnsi the direction perpendicular to the surface lay.

Some of the parameters depend on the definition of a local minimum and a local maximum. The Texture Aspect Ratio Parameters, Str20 and Str37are used to identify texture strength uniformity of texture aspect.

The Mean Half Wavelength, Shwis based on the integrated radial ahsi. Here, a local minimum is defined as anwi pixel where all eight neighboring pixels are higher and a local maximum as a pixel where all eight neighboring pixels are lower. Root Mean Square Gradient. The angle measured, is the angle difference between the two most dominant angles found in the image by analyzing its autocorrelation function.

With this definition the Stdi value is always between 0 nasi 1.

### ASME B / ANSI/ASME B – Surface Texture and Gaging for Screw Threads Package

The Radial Wave IndexSrwiis a measure of how dominant the dominating radial wavelength is, and is defined as the average amplitude sum divided by the amplitude sum of the dominating wavelength:. If the surface is fractal the Log Log graph should be highly linear, with at negative slope.

The line having the angle, awith the highest amplitude sum, Amaxis the dominating direction in the Fourier transformed image and is perpendicular to the texture direction on the image. For a surface with a dominant lay, the parameters will tend towards 0. The Surface Skewness, S skdescribes the asymmetry of the height distribution histogram, and is defined as:.

Area Root Mean Square Slope. Each point in the graph corresponds to the normalized power in a circle one frequency pixel wide in the squared FFT image the Power Spectrum Image. These parameters are the density of summits, the texture direction, the dominating wavelength and two index parameters. We calculate Std from the Fourier spectrum.

These lines are marked Z 0. It is therefore important to include the measurement conditions when reporting roughness data. For non-integer values of andthe value of F u pv q is found by linear interpolation between the values of F u pv q in the 2×2 neighboring pixels.

Having found r 0. Note,that negative peak artifacts may cause this parameter to be underestimated and in such cases it might b4.1 appropriate to perform some noise filtering.