1、BRITISH STANDARD BS 6740:1987 ISO 4291:1985 Method for Determining departures from roundness by measuring variations in radius ISO title: Methods for the assessment of departure from roundness Measurement of variations in radius UDC 620.166:514.112.6 + 514.113.6BS6740:1987 This British Standard, hav
2、ing been prepared under the directionof the General Mechanical Engineering Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 27February1987 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference GME/10 Draft f
3、or comment 83/74606 DC ISBN 0 580 15430 0 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Committee (GME/-) to Technical Committee GME/10 upon which the following bodies were represented: Departme
4、nt of Trade and Industry (National Engineering Laboratory) Department of Trade and Industry (National Physical Laboratory) GAMBICA (BEAMA Ltd.) Gauge and Tool Makers Association Institution of Production Engineers Loughborough University of Technology Ministry of Defence University of Warwick Coopte
5、d member Amendments issued since publication Amd. No. Date of issue CommentsBS6740:1987 BSI 09-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and field of application 1 2 Reference 1 3 Definitions 1 4 Instruments 1 Annex A Departure from roundness of the
6、measured profile of the workpiece 4 Annex B Procedure 7 Annex C Calibration 11 Annex D Determination of systematic errors of rotation 12 Annex E Rules for plotting and reading polar graphs 14 Annex F Determination of least squares centre and circle 17 Figure 1 Spherical stylus 1 Figure 2 Cylindrical
7、 stylus 1 Figure 3 Toroidal (hatchet) stylus 2 Figure 4 Ovoidal stylus 2 Figure 5 Typical transmissions showing rate of attenuation given by two independent C-R networks of equal time constant 3 Figure 6 Assessment of roundness from least squares centre, %Z q 4 Figure 7 Assessment of roundness from
8、minimum zone centre, %Z z 5 Figure 8 Assessment of roundness from centre of minimum circumscribed circle, %Z c 6 Figure 9 Assessment of roundness from centre of maximum inscribed circle, %Z i 7 Figure 10 Slight increase of the radius of the eccentric plot in the perpendicular direction 8 Figure 11 I
9、nclination of the axis of the workpiece to the axis of rotation 8 Figure 12 Choice of direction of measurement for a conical or toroidal workpiece 8 Figure 13 Ball-bearing raceway 9 Figure 14 Closely and widely spaced irregularities 9 Figure 15 Effect of stylus radius when in contact with surface 10
10、 Figure 16 Traces by hatchet and sharp styli 11 Figure 17 Errors in measurement resulting from variation of the offset 11 Figure 18 Dynamic calibration 12 Figure 19 Illustrations of spindle errors and test piece out-of-roundness 13 Figure 20 Example of spindle error and test piece error 14 Figure 21
11、 Avoidance of excessive distortion due to polar plotting 15 Figure 22 Angular relationships 15 Figure 23 Diametral variations 16 Figure 24 Convex surfaces which appear concave after magnification 16 Figure 25 Determination of least squares centre and circle 17 Table Limiting values of upr 2 Publicat
12、ion referred to Inside back coverBS6740:1987 ii BSI 09-1999 National foreword This British Standard, which has been prepared under the direction of the General Mechanical Engineering Standards Committee, is identical with ISO4291:1985 “Methods for the assessment of departure from roundness Measureme
13、nt of variations in radius”, published by the International Organization for Standardization (ISO). Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are
14、not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear,
15、referring to this standard, they should be read as “British Standard”. Textual error. When adopting the text of the International Standard, an error inFigure 5 was discovered. It has been marked in the text and has been reported to ISO in a proposal to amend the text of the International Standard. A
16、 British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-reference International Standard Cor
17、responding British Standard ISO 6318:1985 BS 3730 Assessment of departures from roundness Part 1:1987 Glossary of roundness measurement terms (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 18, an inside back cover and a back cover
18、. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6740:1987 BSI 09-1999 1 1 Scope and field of application This International Standard specifies a method for determining departures
19、 from roundness by measuring variations in radius by means of contact (stylus) instruments. It establishes a) types of instruments and general requirements; b) recommendations for the use of instruments; c) procedures for calibration of instruments and verification of their characteristics. This Int
20、ernational Standard applies to the assessment of the departures from ideal roundness of a workpiece through the medium of a profile transformation, obtained under reference conditions, expressed with respect to any one of the following centres: a) centre of the least squares circle; b) centre of the
21、 minimum zone circle; c) centre of the minimum circumscribed circle; d) centre of the maximum inscribed circle. Each of these centres may have its own particular application. The position of the least squares centre can be calculated from a simple explicit equation given inAnnex F. Departures from r
22、oundness of the measured profile, procedure, calibration and determination of systematic errors of rotation are dealt with inAnnex A to Annex D, respectively. Annex E gives rules for plotting and reading polar graphs. NOTE 1Profile transformation is defined in ISO6318. NOTE 2Reference conditions inc
23、lude the stylus, frequency limitations of an electric wave filter (if used), permissible eccentricity of the graphical or digital representation of the profile (generally7% to15% of its mean radius, seeAnnex E), the position of the measured section or sections relative to some feature of the workpie
24、ce. 2 Reference ISO 6318, Measurement of roundness Terms, definitions and parameters of roundness. 3 Definitions For the purposes of this International Standard, the definitions given in ISO6318 apply. 4 Instruments 4.1 Instrument types and general requirements Instruments of the stylus type employe
25、d for the determination of departures from ideal roundness may be of one of two types: a) a stylus and transducer rotating round a stationary workpiece; b) a rotating workpiece engaged by a stationary stylus and transducer. According to the nature of the output information, instruments for the measu
26、rement of roundness fall into two groups: a) profile recording; b) with direct display of the values of the parameters. Both groups may be combined in one instrument. Stylus instruments should comply with the requirements of4.1.1 to 4.1.3. 4.1.1 Stylus types and dimensions The surface characteristic
27、s of the part under examination are of primary importance in the choice of stylus. Variations to meet different requirements, depending upon the nature and magnitude of the irregularities which are to be taken into account, are permitted as shown inFigure 1 toFigure 4 (see also clauseB.3). Figure 1
28、Spherical stylus Figure 2 Cylindrical stylusBS6740:1987 2 BSI 09-1999 The dimensions r and R of the various styli shall be selected from the following values: 0,25; 0,8; 2,5; 8 and 25 mm. 4.1.2 Stylus static force The force shall be adjustable up to0,25N and in use shall be adjusted down to the lowe
29、st value that will ensure continuous contact between the stylus and the surface being measured. 4.1.3 Instrument response for sinusoidal undulations The range of periodic sinusoidal undulations per revolution (upr) (i.e. per360 ) of the workpiece to which the instrument responds shall be terminated
30、by values taken from the table. Table Limiting values of upr The response at the rated termination of the band shall be75% of the maximum transmission within the band except for1 upr which represents direct mechanical coupling between input and output, Seenote2c). The transmission characteristics of
31、 the filter shall be equivalent to those produced by two independentC-R 1)networks of equal time constant (seeFigure 5). These curves show only the amplitude attenuation characteristics and do not take phase shift into account. A phase corrected filter of known characteristics giving the same rate o
32、f attenuation may be used provided that these characteristics are indicated in the test report. NOTE 1When a filter attenuating high frequencies is required, the two C-R form will generally be acceptable, distortion of the transmitted profile due to phase shift of the high relative to the low freque
33、ncies being generally unimportant. When a filter attenuating low frequencies is required, distortion due to phase shift may be more significant and have to be taken into account, or avoided by using a phase corrected filter. NOTE 2a)It is necessary to distinguish clearly between the undulations per
34、revolution (i.e. per360 ) of the workpiece and the response of electronic circuits in the instrument in hertz. 2) The frequency, in hertz, generated by the instrument will be given by the number of sinusoidal undulations per360 of the workpiece multiplied by the number of revolutions per second of t
35、he spindle. NOTE 2b)Eccentricity will count as1 upr. A sinusoidal component of1 upr will be found when the periphery of the workpiece is assessed from a centre other than the centre of the least squares circle. NOTE 2c)When electronic circuits of instruments are required to respond down to1 upr, the
36、y are often made responsive down to zero frequency (0 Hz), this being a natural way of avoiding phase distortion and permitting calibration by static means. 4.2 Instrument errors 4.2.1 Overall instrument error This is the difference between the value of the parameter indicated, displayed or recorded
37、 by the instrument and the true value of this parameter. The value of this error is determined when measuring a test piece. The overall instrument error shall be expressed as a percentage of the upper limiting value of the measuring range used. This error comprises systematic and random components f
38、rom the spindle error, electric noise, vibration, magnification, etc. Figure 3 Toroidal (hatchet) stylus Figure 4 Ovoidal stylus Filters transmitting from 1 upr up to Filters rejecting below 15 50 150 500 1 500 15 50 150 1) “C” stand for “capacitive”, “R” for “resistive”. 2) 1 Hz = 1 cycle per secon
39、dBS6740:1987 BSI 09-1999 3 4.2.2 Errors of rotation of the instrument The errors of rotation are determined under reference conditions at assigned positions of measurement: a) radial instrument error the value of the roundness parameter which would be indicated by the instrument when measuring a per
40、fectly round and perfectly centred section of a test piece, in a direction perpendicular to the reference axis of rotation; b) axial instrument error the value derived from the zonal parameter displayed by the instrument when measuring on a perfectly flat test piece set perfectly perpendicular to th
41、e reference axis of rotation. NOTEThe components of errors of rotation are vector quantities and should not therefore be algebraically added to the measured value of a roundness parameter in an attempt to allow for errors of rotation. 4.2.3 Statements of errors of rotation The rotating member can ex
42、hibit, within the confines of its bearings, combinations of a) radial displacements parallel to itself; b) axial displacements parallel to itself; c) tilt. The magnitude of the radial instrument error, measured at the stylus, depends on the position of the measurement plane along the axis of rotatio
43、n. The magnitude of the axial instrument error depends on the radius at which the flat test piece is measured. The axial and radial positions selected for test shall therefore be stated. The radial instrument error shall be expressed at two stated and well separated positions along the axis or at on
44、e position together with the rate of change of the radial instrument error along the axis. The axial instrument error shall be expressed on the axis and at one stated radius. Figure 5 Typical transmissions showing rate of attenuation given by two independent C-R networks of equal time constant a a S
45、ee national foreword for details of textual error.BS6740:1987 4 BSI 09-1999 Annex A Departure from roundness of the measured profile of the workpiece In this International Standard, the departure from ideal roundness is assessed as the difference between the largest and the smallest radii of the mea
46、sured profile of the workpiece, measured from one or other of the following centres: a) least squares centre (LSC) the centre of the least squares mean circle (seeFigure 6); b) minimum zone centre (MZC) the centre of the minimum zone circle (seeFigure 7). c) minimum circumscribed circle centre (MCC)
47、 the centre of the minimum circumscribed circle for external surfaces (seeFigure 8); d) maximum inscribed circle centre (MIC) the centre of the maximum inscribed circle for internal surfaces (seeFigure 9). The largest and smallest radii, in each case, are commonly used to define a concentric zone. T
48、he width of the zone may be designated by %Z, with a subscript denoting its centre. For the purposes of this International Standard, the following subscripts are used: NOTEThe use of circles drawn on the chart to represent circles fitting the profile of the workpiece assumes that the workpiece is su
49、fficiently well centred on the axis of the instrument (seeB.1.1,Figure 10 andAnnex F). least squares subscript q, thus %Z q minimum width subscript z, thus %Z z minimum circumscribed subscript c, thus %Z c maximum inscribed subscript i, thus %Z i Figure 6 Assessment of roundness from least squares centre, % Z qBS6740:1987 BSI 09-1999 5 Figure 7 Assessment of roundness from minimum zone centre, % Z ZBS6740:1987 6 BSI 09-1999 Figure 8 Assessment of roundness from centre of minimu
