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1、BRITISH STANDARD BS 939:1977 Reprinted, incorporating Amendment No. 1 Specification for Engineers squares (including cylindrical and block squares) UDC 658.652:621.751:531.747.1 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolle
2、d Copy, (c) BSI BS 939:1977 This British Standard, having been prepared under the direction of the Mechanical Engineering Standards Committee, was published under the authority of the Executive Board on 30 September 1977 BSI 08-1999 First published January 1941 First revision November 1962 Second re
3、vision September 1977 The following BSI references relate to the work on this standard: Committee reference MEE/59 Draft for comment 74/77492 ISBN 0 580 09626 2 Cooperating organizations The Mechanical Engineering Standards Committee, under whose direction this British Standard was prepared, consist
4、s of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Association of Consulting Engineers Association of Hydraulic Equipment Manufacturers Association of Mining, Electrical and Mechanical Engineers British C
5、ompressed Air Society British Electrical and Allied Manufacturers Association (BEAMA) British Gas Corporation British Gear Manufacturers Association British Internal Combustion Engine Manufacturers Association British Pump Manufacturers Association British Steel Corporation Chartered Institution of
6、Building Services Crown Agents for Oversea Governments and Administrations Department of the Environment Department of Industry Department of Industry (National Engineering Laboratory) Department of Trade (Marine Division) Department of Transport Electricity Supply Industry in England and Wales Engi
7、neering 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 Engineers Institution of Production Engineers* London Transport Executive Machine Too
8、l Trades Association Ministry of Defence* National Coal Board Process Plant Association Railway Industry Association of Great Britain The Society of Motor Manufacturers and Traders Ltd Telecommunication Engineering and Manufacturing Association (TEMA) Water-tube Boilermakers Association The organiza
9、tions marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Department of Industry (National Physical Laboratory) Department of Prices and Consumer Protection (British Calibration Se
10、rvice) Gauge and Tool Makers Association Amendments issued since publication Amd. No.Date of issueComments 4239April 1983Indicated by a sideline in the margin Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS
11、939:1977 BSI 08-1999i Contents Page Cooperating organizationsInside front cover Forewordiii Section 1. General 1Scope1 2References1 3Nomenclature and definitions1 4Protection against climatic conditions1 Section 2. Engineers try squares 5Designating size2 6Recommended sizes2 7Material and manufactur
12、e2 8General features of design2 9Finish2 10Accuracy2 11Rigidity5 12Marking5 Section 3. Cylindrical squares 13Designating size5 14Recommended sizes and dimensions5 15Material and manufacture5 16General features of design6 17Finish6 18Accuracy6 19Marking7 Section 4. Solid form block squares 20Designat
13、ing size7 21Recommended sizes and dimensions7 22Material and manufacture7 23General features of design8 24Finish8 25Accuracy8 26Marking9 Section 5. Open form block squares 27Designating size9 28Recommended sizes and dimensions9 29Material9 30General features of design9 31Finish10 32Accuracy10 33Mark
14、ing10 Appendix A Notes regarding bevelled edges of grade AA engineers try squares11 Appendix B Notes on the manufacture and testing of squares11 Figure 1 Exaggerated illustration of deviation from squareness and squareness tolerance1 Figure 2 Engineers try squares3 Figure 3 Squareness of blade edges
15、 to working faces of stock4 Figure 4 Lateral squareness of blade4 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 939:1977 ii BSI 08-1999 Page Figure 5 Rigidity5 Figure 6 Nomenclature for cylindrical squares
16、5 Figure 7 Nomenclature for slid form block squares7 Figure 8 Nomenclature for open form block squares9 Figure 9 Using a bevelled edge11 Figure 10 Method of testing squareness of block squares12 Figure 11 Tilting square tester13 Figure 12 Testing for rigidity14 Table 1 Tolerances on straightness of
17、blade edges2 Table 2 Tolerances on parallelism of blade edges2 Table 3 Tolerances on flatness of working faces of stock3 Table 4 Tolerances of parallelism of working faces of stock3 Table 5 Tolerances on parallelism of side faces of stock3 Table 6 Tolerances on squareness of blade edges to working f
18、aces of stock4 Table 7 Tolerances on lateral squareness of blade to base of stock5 Table 8 Recommended sizes and dimensions of cylindrical squares6 Table 9 Tolerances on cylindrical squares6 Table 10 Recommended sizes and dimensions of solid form block squares7 Table 11 Tolerances on flatness, paral
19、lelism and squareness of working faces (solid iron block squares)8 Table 12 Tolerances on flatness and squareness of front and back surfaces8 Table 13 Recommended sizes and dimensions of open form block squares9 Table 14 Tolerances on flatness, parallelism and squareness of working faces10 Table 15
20、Tolerances on flatness and squareness of front and back surfaces10 Publications referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 939:1977 BSI 08-1999iii Foreword This British Stan
21、dard is one of a series for engineers precision measuring equipment that is being revised and metricated to replace the series in imperial units. First published in 1941, when it applied only to the type commonly known as the try square, BS 939 was revised in 1962 to include cylindrical squares and
22、block squares in both solid and open forms. In addition to metrication, a feature of the present revision is the rationalization of the various tolerances. Wherever practicable, they have been made proportional to the length of the square and every effort has been made to maintain a logical relation
23、ship between the tolerances for the various grades. Appendix A and Appendix B provide, respectively, notes regarding bevelled edges of grade AA engineers try squares and on the manufacture and testing of squares. A British Standard does not purport to include all the necessary provisions of a contra
24、ct. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 14, an inside back cove
25、r and a back cover. 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. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Un
26、controlled Copy, (c) BSI iv blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 939:1977 BSI 08-19991 Section 1. General 1 Scope This British Standard specifies requirements for engineers try squares (excl
27、uding adjustable squares), cylindrical squares and block squares of solid or open form. Section 1 specifies general requirements applicable to all types of square. Section 2 specifies requirements for engineers try squares in three grades of accuracy, AA, A and B, with inner lengths of blade from 50
28、 mm up to and including 1 000 mm. Section 3 specifies requirements for cylindrical squares in accuracy grade AA in sizes from 75 mm up to and including 750 mm. Section 4 specifies requirements for solid form block squares in accuracy grades AA and A in sizes from 50 mm 40 mm up to and including 1 00
29、0 mm 1 000 mm. Section 5 specifies requirements for open form block squares in accuracy grades A and B in sizes from 150 mm 100 mm up to and including 600 mm 400 mm. NOTEWhile the standard provides for squares in various grades of accuracy, it should be noted that their accuracy in use is dependent
30、upon the flatness of the surfaces on which they are used. 2 References The titles of the publications referred to in this standard are listed on the inside back cover. 3 Nomenclature and definitions For the purposes of this British Standard the nomenclature given in Figure 2(a), Figure 6, Figure 7 a
31、nd Figure 8 for the various types of square has been adopted, and the following definitions apply. 3.1 deviation from straightness and flatness the minimum distance between two parallel planes that just enclose the surface under consideration 3.2 deviation from parallelism the difference between the
32、 maximum and minimum distances separating the surfaces or edges under consideration 3.3 squareness of two surfaces 3.3.1 deviation from squareness the minimum distance between two parallel planes that will just enclose one surface (A), including any straightness error of surface (A), and that are pe
33、rpendicular to a datum plane in contact with the other surface (B) (see Figure 1) 3.3.2 squareness tolerance the maximum permissible deviation from squareness (see Figure 1) 3.4 tolerances the maximum permissible deviations from straightness, flatness, parallelism and squareness 4 Protection against
34、 climatic conditions All surfaces of the squares shall be protected against climatic conditions by being covered with a suitable corrosion preventative preparation or a paper impregnated with a vapour phase inhibitor (VPI). Temporary (easily removable) corrosion preventatives are dealt with fully in
35、 BS 1133-6. Guidance on sealed packs with desiccants is given in BS 1133-19. Figure 1 Exaggerated illustration of deviation from squareness and squareness tolerance Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) B
36、SI BS 939:1977 2 BSI 08-1999 Section 2. Engineers try squares 5 Designating size The designating size of an engineers try square is the length of the blade from its tip to the inner working face of the stock (see Figure 2). 6 Recommended sizes Recommended sizes of engineers try squares are: 50, 75,
37、100, 150, 200, 300, 450, 600, 800 and 1 000 mm. Squares of other sizes should be ordered only when it is not practicable to adopt one of the recommended sizes. If squares of intermediate sizes are supplied they should be made to the same tolerances as those specified for the next smaller recommended
38、 size. 7 Material and manufacture All engineers try squares shall be made of good quality steel. The working surfaces of grades AA and A squares shall be hardened to a value of not less than 600 HV and subjected to an appropriate stabilization process. 8 General features of design 8.1 When the blade
39、 and stock of a try square are built up from separate parts, the blade shall be rigidly and permanently fixed in the stock. Grade AA try squares shall have the inner and outer edges of the blade bevelled so that the approximate width of the reduced edge is as follows (see also Appendix A). 8.2 For a
40、ll three grades of try square the stock shall be relieved at the junction of the inner edge of the blade and the inner working face of the stock see Figure 2(a). The inner working face of the stock may be terminated at its junction with the inner edge of the blade, in which case the area of the work
41、ing face of the stock, which projects along both sides of the blade, shall be relieved below the plane of the working face of the stock see Figure 2(b). NOTEThe blade may be recessed from the outer working face of the stock by not more than 0.5 mm see Figure 2(b). 9 Finish All working surfaces of th
42、e blade and stock of the three grades of engineers try square shall have a lapped, finely ground or polished finish, having a surface roughness value of 1.0 4m Ra maximum, and all sharp edges shall be removed (see BS 1134). 10 Accuracy 10.1 Straightness of inner and outer edges of blade. Each edge o
43、f the blade shall be straight to within the tolerance specified in Table 1 when the outer working face or side face of the stock is resting on a horizontal surface. Table 1 Tolerances on straightness of blade edges 10.2 Parallelism of blade edges. The blade edges shall be parallel to each other to w
44、ithin the tolerances specified in Table 2. Table 2 Tolerances on parallelism of blade edges 1234 Size of squareTolerance Grade AAGrade AGrade B mm4m4m4m 50 and 75 100 and 150 200 300 450 600 800 1 000 2 2 2 3 4 6 8 10 4 4 4 6 8 12 16 20 8 8 8 12 16 24 32 40 1234 Size of squareTolerance Grade AAGrade
45、 AGrade B mm4m4m4m Up to 150 200 and 300 400 and 600 800 and 1 000 3 3 7 12 5 8 12 18 8 12 18 24 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 939:1977 BSI 08-19993 10.3 Flatness of working faces of stock.
46、 Each working face of the stock shall be flat to within the tolerance specified in Table 3. Deviations from flatness shall be of concave nature to prevent rock. Table 3 Tolerances on flatness of working faces of stock 10.4 Parallelism of working faces of stock. The working faces of the stock shall b
47、e parallel to within the tolerances specified in Table 4. Table 4 Tolerances of parallelism of working faces of stock 10.5 Parallelism of side faces of stock. The side faces of the stock shall be parallel to within the tolerance specified in Table 5. Table 5 Tolerances on parallelism of side faces o
48、f stock Figure 2 Engineers try squares 1234 Size of squareTolerance Grade AAGrade AGrade B mm4m4m4m 50 and 75 100 and 150 200 300 450 600 800 1 000 1 1.5 2 2 2.5 4 5 6 2 3 4 4 5 8 10 12 4 6 8 8 10 16 20 24 1234 Size of squareTolerance Grade AAGrade AGrade B mm4m4m4m Up to 150 200 and 300 450 and 600
49、 800 and 1 000 2 3 5 8 3.5 5 8 12 5 8 12 16 Size of squareTolerance All grades mm4m Up to and including 150 200 and 300 450 and 600 800 and 1 000 25 50 100 150 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:14:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 939:1977 4 BSI 08-1999 10.6 Squareness of side faces of stock to working faces of stock. The side faces of the stock shall be square to the working faces as follows. Grade AA to wi
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