1、BRITISH STANDARD BS 5204-2: 1977 (Reprinted, incorporating Amendment No. 1) Specification for Straightedges Part 2: Steel or granite straightedges of rectangular section UDC 621.753.3:531.717.862 032.521 + 531.717.862 034.14BS5204-2:1977 This British Standard, having been prepared under the directio
2、nof the Mechanical Engineering Standards Committee, was published underthe authority of the Executive Board on 29 April 1977 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference MEE/59 Draft for comment 75/70860 DC ISBN 0 580 09623 8 Cooperating organizat
3、ions The Mechanical Engineering Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and professional and industrial organizations: Associated Offices Technical Committee Association of Consulting Engin
4、eers Association of Hydraulic Equipment Manufacturers Ltd. Association of Mining Electrical and Mechanical Engineers British Compressed Air Society British Electrical and Allied Manufacturers Association British Gas Corporation British Gear Manufacturers Association British Internal Combustion Engin
5、e Manufacturers Association British Mechanical Engineering Confederation British Pump Manufacturers Association British Steel Corporation British Steel Industry Chartered Institution of Building Services Crown Agents for Oversea Governments and Administration Department of the Environment Department
6、 of Industry Department of Trade Electricity Supply Industry in England and Wales Engineering Equipment Users Association Federation of Manufacturers of Construction Equipment and Cranes Health and Safety Executive Institution of Gas Engineers Institution of Mechanical Engineers Institution of Plant
7、 Engineers Institution of Production Engineers* London Transport Executive Machine Tool Trades Association Ministry of Defence* National Coal Board National Engineering Laboratory Department of Industry* Process Plant Association Railway Industry Association of Great Britain Royal Institute of Briti
8、sh Architects Society of Motor Manufacturers and Traders Ltd. Telecommunication Engineering and Manufacturing Association The Water-tube Boilermakers Association The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the follow
9、ing, were directly represented on the committee entrusted with the preparation of this British Standard: Department of Prices and Consumer Protection Gauge and Toolmakers Association Individual experts Amendments issued since publication Amd. No. Date of issue Comments 4128 November 1982 Indicated b
10、y a sideline in the marginBS5204-2:1977 BSI 08-1999 i Contents Page Cooperating organizations Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Material and manufacture 1 5 Recommended sizes and design 1 6 Finish 1 7 Points of support for straightedges of 1 m length and over
11、1 8 Accuracy 2 9 Case 3 10 Protection against climatic conditions 3 11 Marking 3 Appendix A Note on supporting straightedges of rectangular section 4 Appendix B Recommended methods of testing straightness of a straightedge 5 Figure 1 Position of handling slots 2 Figure 2 Alternative methods of indic
12、ating the positions of support 2 Figure 3 Deflection with supports at ends 5 Figure 4 Deflection with supports near the centre 5 Figure 5 Optimum position for supports 5 Figure 6 Test by inclination method 6 Figure 7 Plotting of readings 7 Figure 8 Method of compensation for mass of level 8 Table 1
13、Minimum section 2 Table 2 Tolerance on straightness of working face 2 Table 3 Tolerance on parallelism of working face 3 Table 4 Combined tolerance on flatness and parallelism of side faces 3 Table 5 Best positions for supporting straightedges 4 Table 6 Example of recording observations 7 Publicatio
14、ns referred to Inside back coverBS5204-2:1977 ii BSI 08-1999 Foreword This Part of BS 5204 is published under the authority of the Mechanical Engineering Standards Committee. In accordance with the policy of publishing metric versions of British Standards for engineers precision measuring equipment,
15、 those standards for straightedges have now been revised. Cast iron straightedges, bow shaped and I-section, previously covered by BS 818 “Cast iron straightedges (bow shaped and I-section)” are the subject of Part 1 of BS5204. Part 2 of this standard deals with steel and granite straightedges and r
16、eplaces BS 863 “Steel straightedges of rectangular section” which is now withdrawn. A British Standard does not purport to include all the necessary provisions of contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself
17、 confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indic
18、ated in the amendment table on theinside front cover.BS5204-2:1977 BSI 08-1999 1 1 Scope This Part of BS 5204 specifies requirements for steel or granite straightedges up to and including 2 m in length, of rectangular section, with or without a bevelled edge, and with both working faces finished str
19、aight and parallel. Two grades of accuracy are provided for: grade A and grade B. Appendices deal with the method of supporting straightedges of rectangular section and methods of testing straightness of a straightedge. 2 References The titles of the publications referred to in this standard are lis
20、ted on the inside back cover. 3 Definitions For the purposes of this Part of this British Standard the following definitions apply. straightness tolerance of working face the straightness tolerance is the maximum permissible separation of two parallel planes between which the face lies tolerance on
21、parallelism of working face the tolerance on parallelism is the maximum permissible variation in width between the surfaces under consideration 4 Material and manufacture 4.1 Steel straightedges. Grade A straightedges shall be made from high quality steel. Their working faces shall be hardened to no
22、t less than 500 HV. Grade B straightedges may be supplied hardened or unhardened. If supplied hardened they shall be made from high quality steel and their working faces shall be hardened to not less than 500 HV. If supplied unhardened they shall be made from cast steel. NOTEIf the purchaser specifi
23、cally requires grade B straightedges to be hardened he should state this in his enquiry or order. In the absence of such specific requirements the straightedges may be supplied hardened or unhardened at the option of the manufacturer. Manufacturers are required to take reasonable precautions to ensu
24、re that finished straightedges are free from internal stress. 4.2 Granite straightedges. Grade A or grade B straightedges may be made of granite. The rock shall be close grained and of uniform texture, free from flaws and fissures and from inclusions of softer materials. The colour of the granite, w
25、hich is dependent on the mineral composition, is of no importance, but the colour of any individual straightedge shall be uniform. Granite straightedges may be supplied with handles and with threaded inserts if required. The positions of the inserts may be specified by the manufacturer or as request
26、ed by the customer, but no insert periphery shall be less than 20 mm from any edge. When threaded inserts are provided they shall be M6 to class 6H tolerance, or in the case of straightedges longer than 1000 mm, M10 to class6H tolerance, in accordance with BS 3643-2:1966. 5 Recommended sizes and des
27、ign Recommended lengths are 300, 500, 1000, 1500 and 2000 mm. Minimum sections shall be as shown in Table 1. Straightedges of intermediate lengths should be ordered only when it is not practicable to adopt one of the recommended lengths. Such straightedges shall comply with the minimum depths and th
28、icknesses given in Table 1 for the next longer recommended length. The side surfaces may be slightly relieved (I-section) to reduce weight, and long straightedges may be provided with two slots for ease in handling; the centres of these slots should be at points two-ninths of the length from each en
29、d of straightedges (seeFigure 1). 6 Finish The working faces shall be finished by grinding or lapping. All sharp edges shall be removed. 7 Points of support for straightedges of 1 m length and over To ensure minimum deflection on straightedges of1m length and over, the positions for supporting the s
30、traightedges when used on edge should be located two-ninths of the length from each end (seeAppendix A) and shall be marked on one or both side faces by arrows and the word “support” engraved on the face, as shown in Figure 2. NOTEThe attention of manufacturers is drawn to the recommendation in A.2.
31、BS5204-2:1977 2 BSI 08-1999 Table 1 Minimum section 8 Accuracy Each straightedge shall comply with the requirements of 8.1 to 8.4 for grade A or grade B accuracy. 8.1 Straightness tolerance of working face. When the straightedge is lying flat on a grade AA surface plate (as specified in BS 817:1972)
32、 or standing “on edge” supported at two points two-ninths of the length from each end, the permitted tolerances on straightness are given in Table 2. 8.2 Tolerance on parallelism of working face. The tolerances on parallelism are given in Table 3. Table 2 Tolerance on straightness of working face Di
33、mensions in millimetres Length Steel Granite Grades A and B Grade A Grade B Depth Thickness Depth Thickness Depth Thickness L d t d t d t 300 40 6 30 5 75 25 500 50 10 45 6 100 35 1 000 75 10 60 8 125 40 1 500 100 12 70 10 150 50 2 000 125 13 80 12 150 50 Figure 1 Position of handling slots Figure 2
34、 Alternative methods of indicatingthe position of support Dimensions in millimetres Length of straightedge or length under test Tolerance Grade A Grade B 300 0.005 0.010 500 0.005 0.010 1 000 0.008 0.015 1 500 0.012 0.025 2 000 0.015 0.030 NOTE 1The tolerances above apply to the overall length and t
35、o intermediate lengths of a straightedge. NOTE 2Recommended methods of testing straightness are dealt with in Appendix B. NOTE 3Tolerances on straightness of the working face for straightedges with lengths other than those listed in Table 2 can be calculated at the rate of 0.00075 mm per 100 mm for
36、grade A and 0.0015 mm per 100 mm for grade B, with a minimum of 0.005 mm for grade A and 0.010 mm for grade B. Grade A tolerances are to be rounded up to the nearest0.001mm and grade B tolerances expressed to the nearest 0.005 min.BS5204-2:1977 BSI 08-1999 3 Table 3 Tolerance on parallelism of worki
37、ng face 8.3 Combined flatness and parallelism of side faces. When the straightedge is laid flat with either of its side faces on a true surface (see 8.1) the upper face shall be parallel to the plate to within the tolerances given in Table 4. 8.4 Squareness of side faces to working faces. The square
38、ness of the side faces to the working faces shall be within 0.001 mm per millimetre of depth for grade A and within 0.002 mm per millimetre of depth for grade B. Table 4 Combined tolerance on flatness and parallelism of side faces 9 Case It is recommended that each straightedge be provided with a su
39、itable case or protective cover of substantial construction. 10 Protection against climatic conditions All finished surfaces of the straightedge shall be protected against the effects of climatic conditions. 11 Marking Each straightedge shall be legibly and permanently marked with the following part
40、iculars. a) The manufacturers name or trade mark. b) The number of this British Standard, i.e.BS5204-2. c) Grade A or B, as appropriate. d) When hardened in accordance with 4.1, the word “Hardened”. e) The year of manufacture. NOTE 1The mark BS 5204-2 on the product is a claim by the manufacturer th
41、at it complies with the requirements of Part 2 of this standard. NOTE 2Inspection of straightedges and certification that they comply with the requirements of this standard may be undertaken by laboratories approved by the British Calibration Service; addresses can be obtained on application to the
42、Director, British Calibration Service, National Physical Laboratory, Teddington, Middlesex, TW11 0LW. Dimensions in millimetres Length of straightedge Tolerance Grade A Grade B 300 0.005 0.010 500 0.005 0.010 1 000 0.008 0.015 1 500 0.012 0.025 2 000 0.015 0.030 Dimensions in millimetres Length of s
43、traightedge Tolerance Grade A Grade B 300 0.05 0.07 500 0.05 0.07 1 000 0.07 0.10 1 500 0.09 0.14 2 000 0.11 0.17BS5204-2:1977 4 BSI 08-1999 Appendix A Note on supporting straightedges of rectangular section A.1 General When straightedges are used on edge, it should be realized that although they ma
44、y be of comparatively deep section, they are liable to deflect under their own mass. The amount of deflection will vary according to the number and the positions of the supports along the length of the straightedge. Consider, for example, the case of a grade A steel straightedge, 1500 mm long with a
45、 section of100mm 12 mm. If this rests on edge on two supports placed at its extremities, as in Figure 3, it will sag at the middle by 0.025 mm. Alternatively, if the supports are brought close together at the middle of the bar, as in Figure 4, the ends will droop by 0.012 mm. Thus, if such a straigh
46、tedge were rested on edge on a surface which happened to be concave by as much as 0.025 mm, or convex by as much as 0.012 mm, over 1500 mm, the straightedge would rest in contact with the surface in both cases over its whole length, and one might be deceived into considering the surface as being fre
47、e from any appreciable errors in straightness. However it is evident from Figure 3 and Figure 4 that there is an intermediate position for the two supports at which the distortion of the straightedge under its own mass is reduced to a minimum. This position is shown in Figure 5. With the supports in
48、 this optimum position, the deflection of the straightedge under consideration is reduced to as low as 0.0007 mm. The disposition of the supports shown in Figure 5 should always be adopted when using steel straightedges of rectangular section on edge. For example, when testing the straightness of a
49、horizontal surface with such a straightedge, the latter should be supported at the positions indicated in Figure 5 on two gauge blocks of equal height (say2.5 mm) and the parallelism of the gap between the surface and the lower edge of the straightedge should be tested by means of other gauge blocks. Table 5 shows the best positions for supporting straightedges of various lengths from 300 mm upwards. Table 5 Best positions for supporting straightedges A.2 Advice to manufacturers In order to acquaint users of straighte
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