Bs 1134 pdf

In such cases, the suffix max shall be added to the parameter symbol, as shown in the following example: Ry max When both lower and upper limit values need to be specified, these shall be expressed in 4m as shown in the following examples: Ra 0. If a single value is stated it shall be the upper limit value and shall be expressed in 4m as shown in the following examples: Ra 0.

Unless otherwise specified, the implication is that the surface roughness should be measured across the direction of the lay. The nominal value of the tip radius of the stylus shall be one of the following: a 2 0. See also Appendix C. The nominal value of the stylus angle shall be one of the following: a 1. The static measuring force shall be sufficient to ensure continuous contact between the stylus and the surface being measured and shall be not greater than that given in Table 2.

Table 2 Static measuring force of the stylus Nominal tip Maximum static radius of stylus measuring force at mean level of stylus. If a skid is employed, its radius in the direction of the traverse shall be not less than 50 times the meter cut-off used.

If two simultaneously operative skids, as shown in Figure 19, are used, their radii shall be not less than eight times the meter cut-off. NOTE Although the use of the skid may, when applied under suitable conditions, introduce no error of any great practical significance, external datum units should be used in all serious metrological work such as, for example, calibration procedures, and in the case of surfaces of limited area or requiring the use of cut-off values of 2.

Figure 19 Stylus acting midway between two skids 6. The surface roughness of the skid as determined by the ten point height of irregularities, Rz, shall be not greater than 0. The force exerted by the skid on the surface to be measured shall be not greater than 0. Horizontal Vh : 10, 20, 50, , , , 1 , 2 , 5 , 10 , 20 , 50 The rate of attenuation shall be equivalent to that produced by two independent C-R networks of equal time constant in series.

The transmission coefficient of such a system shall be given by the equation:. These are deemed to be equivalent to the sampling lengths in Table 1. NOTE In a practical determination, the values of the transmission coefficients for the characteristics shown are measured relative to the flat part of the transmission curve see Figure The cut-off values in mm to be used in instrument construction shall be selected from the following series: 0.

NOTE 1 A cut-off of 0. NOTE 2 Nominal sinusoidal frequency response characteristics for a profile instrument are shown by the ratios given in Table 4 see also Figure Figure 20 Profile instrument frequency response Table 4 Nominal sinusoidal frequency response characteristics for a profile instrument Wavelength. NOTE Because of practical difficulties in measurement at the very short wavelengths involved, the electrical transmission characteristic for 0.

NOTE The admissible basic error of calibration thus expressed does not include the effect of deviations in the transmission characteristic which will be additional thereto.

Table 5 Upper and lower limits of transmission coefficients Wavelength, 2. NOTE An explanation of the method divergence of the instrument reading see 2.

Perpendicular to the plane of projection of the view in which the symbol is used. Crossed in two slant directions relative to the plane of projection of the view in which the symbol is used.

Approximately circular relative to the centre of the surface to which the symbol is applied. Approximately radial relative to the centre of the surface to which the symbol is applied. NOTE Should it be necessary to specify a direction of lay not clearly defined by these symbols, this may be done by a suitable note on the drawing.

Appendix A Parameter values Values are normally determined as mean results from the measurement of several sampling lengths taken consecutively along the profile. These may be determined graphically in accordance with clause 4 or by direct reading instruments.

The direction in which the measurement is made should in general be approximately at right angles to the lay if the surface texture has a directional quality see Figure The parameter values specified should be selected from the ranges of preferred values given in Table 6, Table 7 and Table 8.

Table 6 Preferred nominal values for arithmetical mean deviation of the profile Ra. Table 7 Preferred nominal values for ten point height of irregularities Rz , and maximum height of the profile Ry 4m.

Table 8 Preferred nominal values for mean spacing of profile irregularities Sm , and mean spacing of local peaks of the profile S mm. NOTE The values given in Table 6, Table 7 and Table 8 are expressed as preferred in order to discourage unnecessary variation of the values expressed on drawings. It should be realized that in some circumstances, other values may be specified.

Appendix B Method divergence of instrument reading B. Thus the two methods referred to in this standard for selecting the texture to be measured by sampling length and cut-off , although deemed to be acceptable equivalents of each other, treat the profile in different ways that may lead to slightly different numerical evaluations. For short wavelengths and most machined surfaces the divergence is usually small, and this is generally the case for random profiles.

It is usual to accept the instrument reading as the operative basis for grading workpieces in the workshop, and to avoid extreme divergences by use of a sufficient cut-off. Table 9 Comparison of Ra values obtained by graphical and instrumental means Type of surface.

NOTE Mean method divergence for 2. Mean method divergence for 0. These mean method divergences and standard deviations were obtained from measurements on 22 surfaces. This is generally not a straight line but an undulating one which weaves its way through the profile as shown in Figure The undulations account for the method divergence. Equations and computing tables for the electrical mean line found by the standard filter are available from manufacturers, and these can serve as a basis for determining precisely, by computation from digitized profile records, the errors of instruments complying with this standard.

In practice, however, it is generally only in the case of precise instrument calibration that it is necessary to take the details of filter behaviour fully into account. Appendix C Factors affecting the statement of accuracy C. These errors can be expressed simply, and it is a normal expectation that this should be done.

Surface instruments are more complicated, for the quantity to be measured has generally to be derived from a fluctuating signal representing the profile of a sample of the surface. Errors can arise from different sources having quite different error laws, and the total error does not lend itself to expression in a simple yet meaningful way. Ideally, in addition to being marked with substantially its full value, assuming negligible instrument losses, each specimen should be accompanied by a statement of the reading that should be obtained from it by an instrument having given stylus dimensions and for each mean transmission characteristic.

This is a refinement that has still to be treated in a formal way. The overall amplification is left as an adjustment for the user to make by means of one or more potentiometers which have to be set in conjunction with an instrument calibration specimen or with a calibrated test specimen. The attainable accuracy therefore starts with the calibration specimen and the users skill in allowing for its characteristics and in securing with it the best overall adjustment of the instrument.

It is envisaged that the use of more than one test specimen will become normal practice. However, the working range of the instrument may be considerable, extending vertically from around 0. Even if there is, after initial adjustment, no error in the calibrated region of the range, there may be errors in other regions unless all parts of the instrument function perfectly. These errors would be revealed by other precisely calibrated specimens. It is to the expression of the error throughout the range, relative to the setting-up point, that 7.

Instrument errors can arise from the condition of the stylus and datum device, various electronic sources, and the errors inherent in the output behaviour and reading. Assuming that the stylus is in good order, the radius of its tip may influence the indication. Differences between a 2 4m and a 10 4m tip, while negligible for many surfaces, may be quite significant for others, and especially for very fine ones.

It does not follow that the blunter tip will always give the lower reading, for on some surfaces e. Instrument errors, apart from an error in overall amplification, may include errors due to electrical and mechanical noise, to residual non-linearity, to ratio errors in range switching and, where applicable, to errors in the transmission characteristic.

For most purposes, the noise can be taken as the reading given by a well-polished optical flat, free from scratches. When the proportion of noise in the reading is small, say less than one-third, the noise can be neglected. When it is twice as great as the signal, it becomes dominant. The actual value of the noise, for a given instrument, may vary over a wide range according to the rigidity of the set-up and the amount of vibration in the instrument and its environment.

If an instrument were required to give maximum accuracy over a small range of operation, its adjustment would naturally be optimized for that range. On the other hand, if the instrument were required to perform as well as possible over a wide range without readjustment, the adjustment would be optimized so as to minimize the residual errors throughout the range. The concept of optimum use will refer to environmental conditions, rigidity of workpiece mounting, and the fact that readings near the top of the scale will generally be less subject to error than those near the bottom.

On the other hand, a specification attempting to cover all possible combinations would become impossibly complex and again meaningless. BS , Engineering drawing practice. BS , Recommendations for dimensioning and tolerancing of size. BS , Method for the assessment of surface texture1. BS , General information and guidance. The shape of the curve can provide much information.

A symmetrical profile gives an amplitude distribution curve, which is symmetrical either side of the centre line. An unsymmetrical profile results in a skewed curve. The direction of the skew is dependent on whether the bulk of the material is above the mean line negative skew or below the mean line positive skew. Use of this parameter can distinguish between two profiles having the same Ra value. As an example, a porous, sintered or cast iron surface has a large value of skewness.

One characteristic of a good bearing surface is that it has a negative skew, indicating the presence of comparatively few spikes that could wear away quickly and relative deep valleys to retain oil traces. A surface with a positive skew is likely to have poor oil retention because of the lack of deep valleys in which to retain oil traces.

Surfaces with a positive skewness, such as turned surfaces, have high spikes that protrude above the mean line. Rsk correlates well with load carrying ability and porosity. Unlike Psk, Rsk or Wsk, this parameter cannot only detect whether the profile spikes are evenly distributed but also provides the measure of the sharpness of the profile. A spiky surface has a high kurtosis value and a bumpy surface has a low kurtosis value.

This is a useful parameter for predicting component performance with respect to wear and lubrication retention. However, using the kurtosis parameter, it is not possible to distinguish between a peak and a valley. Kurtosis is expressed mathematically as:. It is the average value of the length of the mean line section containing a profile peak and adjacent valley.

This parameter requires height and spacing discrimination. Key 1 Sampling length. This parameter depends on both amplitude and spacing and is, therefore, a hybrid parameter. The slope of the profile is the angle it makes with a line parallel to the mean line. The mean of the slopes at all points in the profile within the sampling length is known as the average slope. One example of its use is to determine the developed or actual profile length i.

The steeper the average slope, the longer the actual length of the surface is. This parameter is used in painting and plating operations where the length of surface for keying is important. Average slope can be related to hardness, elasticity and crushability of the surface. Where the value is small, the indication is that the surface is a good optical reflector. It is represented as a percentage. The bearing length is the sum of the section lengths obtained by cutting the profile with a line slice level drawn parallel to the mean line at a given level.

Parameter Pmr c , Rmr c , Wmr c determines the percentage of each bearing length ratio of a single slice level or nineteen slice levels which are drawn at equal intervals within Pt, Rt or Wt respectively. By plotting the bearing ratio at a range of depths in the profile, the way in which the bearing ratio varies with depth can easily be seen and provides a means of distinguishing between different shapes on the profile.

The definition of the bearing area fraction is the sum of the lengths of individual plateaux at a particular height, normalized by the total assessment length, and is the parameter designated Rmr see Figure Values of Rmr are sometimes specified on drawings. However, this can lead to large uncertainties if the bearing area curve is referred to the highest and lowest points on the profile.

Many mating surfaces requiring tribological functions are usually produced with a sequence of machining operations. Usually the first operation establishes the general shape of the surface with a relatively coarse finish and further operations refine this finish to produce the properties required by the design. This sequence of operations removes the peaks of the original process but the deep valleys are left untouched. This process leads to a type of. The height distributions are negatively skewed, therefore making it difficult for a single average parameter such as Ra to represent the surface effectively for specification and quality control purposes.

Rmr refers to the bearing ratio at a specified height see Figure One way of specifying the height is to move over a certain percentage the reference percentage on the bearing ratio curve and then to move down a certain depth the slice depth. The bearing ratio at the resulting point is Rmr. The purpose of the reference percentage is to eliminate spurious peaks from consideration as these peaks tend to wear off in early part use.

The slice depth then corresponds to an allowable roughness or to a reasonable amount of wear. The amplitude distribution curve is a probability function that gives the probability that a profile of the surface has a certain height, at a certain position. The curve has the characteristic bell shape of many probability distributions see Figure The curve tells the user how much of the profile lies at a particular height, in terms of a histogram.

Key 1 Mean line 2 Evaluation length 3 Amplitude density. The profile height amplitude curve illustrates the relative total lengths over which the profile graph attains any selected range of heights above or below the mean line see Figure The horizontal lengths of the profile included within the narrow band, dz, at a height, z, are, a, b, c, d and e.

By expressing the sum of these lengths as a percentage of the evaluation length, a measure of the relative amount of the profile at a height, z, can be obtained. Key 1 Profile graph 2 Amplitude distribution curve 3 Amplitude density 4 Evaluation length. This graph is termed the amplitude distribution at height, z. By plotting density against height the amplitude density distributed over the whole profile can be seen. This produces the amplitude density distribution curve. Also included is whether the parameter is calculated over a sampling length or over the evaluation length.

Higher or lower values can be obtained under special conditions. Other components are shown in Figure 17 and include: a pickup, driven by a motor and gearbox, which draws the stylus over the surface at a constant speed; an electronic amplifier to boost the signal from the stylus transducer to a useful level; and a device, also driven at a constant speed, for recording the amplified signal or a computer that automates the data collection.

The part of the stylus in contact with the surface is usually a diamond tip with a carefully manufactured profile. Owing to their finite shape, some styli on some surfaces do not penetrate into valleys and give a distorted or filtered measure of the surface texture. Consequently, certain parameters are more affected by the stylus shape than others. The effect of the stylus forces can affect the measurement results. Where a force is too high it can cause damage to the surface being measured.

Where a force is too low it can prevent the stylus from staying in contact with the surface. For an accurate cross section of the surface to be measured, the user should check that the stylus follows an accurate reference path as it traverses the surface. The user should check that the reference path has the general profile of, and be parallel to, the nominal surface. Such a datum can be developed by a mechanical slideway. There are a number of portable measuring instruments that can be mounted directly onto the surface being measured.

Whilst these measuring instruments have a number of obvious advantages, the user should be aware of the following disadvantages and limitations. These factors should be taken into account when using results obtained under these conditions.

Environmental conditions should be in accordance with the following. The measuring instrument should always be calibrated prior to measurement. Before calibration of the measuring instrument takes place, the stylus should be checked visually for signs of wear or damage. The user should clean the test specimen using an appropriate cleaning method this will vary depending upon the material and check that it is free of dust and dirt. In some cases chemical cleaning is preferable to the use of lint free cloth.

Where the surface texture is coarse, then the cloth might deposit fabric on the surface that could affect the reading. After measurement of the calibration artefact, the indicated value should be compared to the value associated with the calibration artefact. Depending on the measuring instrument used, this adjustment can be carried out in a number of ways.

With measuring instruments that are software or processor based, the sensitivity of the measuring instrument is automatically calibrated by entering the value shown on the calibration certificate into the machine display as prompted. The dimension and shape should be considered when selecting a stylus as it is these features that have an influence on the information gathered during measurement.

The ideal stylus shape is a cone with a spherical tip. However, truncated pyramidal, or chisel shaped tips, 0. A stylus radius should be chosen in accordance with Table 2.

The static measuring force at the mean position of the stylus should be 0. This should not change during the measurement. The manufacturer of the measuring instrument generally sets this force. The tip of the stylus is subject to wear and should be checked on a regular basis. A damaged stylus tip can lead to erroneous measurements. When checking the condition of the stylus the user should record the measuring instrument reading for a chosen surface texture parameter usually Ra against the value for the calibration artefact stated on its calibration certificate.

The size of the stylus can affect the accuracy of the traced profile in a number of ways: penetration into valleys, distortion of the peak shape and re-entrant features. The larger the tip radius, the less likely it is to be able to penetrate to the bottom of the valleys.

This means that the resulting value of a roughness height parameter is lower than the actual value. The stylus follows a path that is more rounded than the peak. As the stylus is raised to its full height when it makes contact with the crest, the actual peak height is measured see Figure A stylus with a spherical tip causes: a the peaks of a profile to become rounded due to the curvature of the stylus tip; and b the depth of the profile valleys to be reduced.

However, the actual peak height is reported accurately. It cannot detect re-entrant features as shown in Figure 19 and is, therefore, unable to measure the actual depth of the valley. Instead, it reports a simpler profile as the stylus slides over the feature to make contact with the next peak.

The resulting decision is likely to be more accurate with the increase in length of the surface being tested and the increase in the number of surface test lengths. However, as costs increase with the increase in measurements taken, the inspection process is often a compromise between reliability and cost. When a component is manufactured from a drawing, the surface texture specification normally includes the sampling length for measuring the surface profile. The most commonly used sampling length is 0.

However, when no indication is given on the drawing the user requires a means of choosing what value to use. The sampling length should only be selected after considering the magnitude of the surface texture and which characteristics are required for the measurement. A value of 0. However, it might not be suitable for assessing a particular feature of the surface texture and so the function of the surface and the precision of the machining process should be taken into account.

Filtering is the procedure that enables the user to separate certain spatial frequency components of the surface profile. The spatial frequency of components present in the electrical waveform that represents the surface is dependent on the spacing of irregularities and on the measuring speed of the measuring instrument. For instance, if the irregularity spacing of a surface is 0. If the irregularity spacing were 0. If a high pass filter were inserted that suppresses any frequency below 4 Hz, only those irregularities of less that 0.

This condition would provide the measuring instrument with a sampling length of 0. By introducing different filters, the sampling length best suited to the surface can be selected. If the same filter were used at a measuring speed of 2 mm per second, the sampling length would be 0. Various sampling lengths can be obtained with the use of a single filter and in conjunction. A roughness filter is used when measuring potential characteristics such as friction, wear, reflectivity, resistance to stress failure and lubricating properties.

Waviness can be filtered out so that the roughness can be observed in isolation. The roughness profile includes only the shortest wavelengths; the longer wavelengths associated with waviness are attenuated.

Roughness is of significant interest in manufacturing as it is often this feature of a surface that defines how it looks, feels and behaves when in contact with another surface. A waviness filter should be used to determine the effects of machine tool performance and also types of component performance such as noise and vibration by removing profile and roughness. Typically, modern measuring instruments have a choice of digital filters that can be selected according to the type of measurement required.

Ideally, the filter characteristics would change instantaneously at the sampling length selected. The amplitudes of shorter wavelength irregularities remain unchanged, while those of the longer wavelength are progressively reduced.

In normal applications this does not significantly affect the value of a surface texture parameter. The closer the irregularities are, the higher the spatial frequency is. The frequency also increases with a faster measuring speed. It is important to consider the relationship between irregularity spacing, measuring speed and signal frequency when measuring surface texture.

To obtain an accurate graph of the surface, the frequencies generated need to be accurately transmitted through the system. A stylus traversing at a measuring speed of 1 mm per second over a surface having peaks regularly spaced at intervals of 0. By halving the measuring speed to 0. The maximum frequency to be handled can be brought within the bandwidth of the system by selecting an appropriate maximum measuring speed.

However, the amplifier frequency response can be modified by the use of a filter. It is therefore possible to separate roughness from waviness. On many surface texture measuring instruments, the measuring speed is fixed by the manufacturer and the end user has no control over this parameter. The subjectivity of those using such methods compromises the accuracy or consistency of the results and this should be taken into account when choosing the best means of assessing the surface texture.

However, while comparative methods tend to be less accurate than using a stylus, they are generally cheaper and more convenient than stylus methods. A typical set of comparison specimens consists of a wallet containing a number of specimens covering example surface textures of various machining operations — turning, milling horizontal and vertical , grinding, lapping and reaming.

The user can compare the machined component with the feel and appearance of the corresponding comparison specimen. The user should check that a comparison block produced by the same production process is used to produce the component that is selected.

Comparison artefacts are available for different processes including flat and cylindrical surfaces. After assessment using a comparison specimen, the surface texture should be given a numerical value. This helps to increase the accuracy of the comparison and reduce the subjectivity of assessment by comparative methods.

Where a work piece is heavy enough that it is unlikely to move when measured, it is not necessary to use a constraint to prevent it from moving. However, where a work piece is small, light and likely to move when measured, clamps or a vice should be used. Where clamping forces are used, the user should check that they do not distort the work piece. Restraining materials that are elastic or can deform easily should not be used, as movement might occur during the measuring process.

The work piece should be aligned to the traverse direction of the measuring stylus within the working range of the measuring instrument. With hand held measuring instruments this is carried out by adjusting the level of the drive unit by the use of tilt adjustment knobs. For tabletop machines a levelling table is often used allowing adjustment in the x and y axes.

Levelling a work piece for measurement at high magnification can require skill and be time consuming. Where the machine is software based and contains the appropriate software, adjustment can be mathematically corrected by the tilt compensation function. It should be noted that the measurement of the work piece cannot be carried out where the level of the work piece is not within the measuring instrument range.

The next stage is for the user to select the parameters required for measurement. At least ten surface measurements should be made, where practicable. Each measurement should be made on a typical surface and measurements should not be made where there are obvious holes, scratches or other machining damage. These can produce anomalies in the readings that can affect the overall surface profile and can be a particular problem when measuring ceramic surfaces.

The measurement traverse can then be made. On computer based measuring instruments, it is sometimes possible to apply files and parameters to a profile after it has been measured. However, the user should still consider applying them before taking measurements in order to obtain a suitable measurement length, speed, etc. On completion of the measurement the results are output in various forms depending on the make and manufacturer of the measuring instrument.

They usually take the form of a trace, a printout of results or a file held in computer memory. By visual examination of the work piece it can be seen whether the surface texture is markedly different over various areas or homogeneous over the whole. Surface texture parameters are not useful for the description of surface defects such as scratches and pores and such structures should not be considered during surface texture inspection.

Where the surface is homogeneous, then parameter values taken from anywhere on the surface can be used for comparison with requirements specified on drawings or specification documents. Where the surface texture is markedly different over the work piece then parameter values determined over each area should be used separately for comparison. For stated requirements that specify the upper limit of the parameter, the areas of the surface that indicate maximum values should be used for comparison.

This rule should only be applied when the measurements are distributed over a representative area of the surface. Where this is not specified then the procedures detailed in The following procedure should be applied. Select the sampling length corresponding to the parameter estimate in a.

If an adjustment was made at e , make a new parameter measurement at the adjusted setting. This value should be in the range for the sampling length used as given in Table 4 or Table 5. If it does not, return to f. Depending on the action taken at e , the measurement from c might already provide some information.

Even ground surfaces show some repetitiveness. On some surfaces these repetitive features are clearly visible, either on the work piece itself or on the profile. The presence of certain repetitive features, however small, can indicate tool wear, machine vibration or machine deficiencies. It is, therefore, important to identify them.

Where a profile is perfectly periodic such as in a sine wave, the relationship of a given group of points repeats exactly at a distance equal to the wavelength. On the normal portable bs surface finish the guide is generally based on a skid which slides over the general surface ensuring that the linked stylus moves in a straight line parallel to the local surface Surface Texture Parameters The identification bs surface finish finjsh surface texture used a number of parameters.

How bx it work? Deviations from the desired form result from clamping marks or sliding marks machining guide errors etc.

Sites Providing Information on surface Finish. Search all products by. You may experience issues viewing this site in Internet Explorer 9, 10 or The identification of the surface texture used a number of parameters. Who should buy it? Guidance eurface general information Withdrawn.

Again there may be more recent versions of the bs surface finish. Roughness Bs surface finish roughness of a manufactured surface generally results from the production process and not specifically from the machining process if any. The action of the cutting tool, chemical action, polishing, lapping, and the structure of the material all contribute to the roughness of the surface.

The Red document status indicator zurface that the document is an bs surface finish version The document has likely been withdrawn by the publisher, also the meta data presented here may be out of date as it is no longer being maintained by the editorial teams at NBS.

BS gives practical guidance on the measurement of surface texture using a stylus instrument. In the roughness requirement this value is the sampling length. Methods and instrumentation Withdrawn. As sueface stylus moves up and down along the surface, the transducer converts finisb movement into a signal which is then exported to a processor which converts this surfaxe a number and usually a visual profile.

These Pages include various standards.