1、BRITISH STANDARD BS 1790:1961 Incorporating Amendment No. 1 Specification for Length bars and their accessories (Imperial Units)BS1790:1961 This British Standard having beenapproved by the MechanicalEngineering IndustryStandards Committeeand endorsed by theChairman of the EngineeringDivisional Counc
2、il,was published undertheauthority of the GeneralCouncil on 31January1961 BSI 01-2000 First published January 1952 First revision January 1961 The following BSI references relate to the work on this standard: Committee reference MEE/59 Draft for comment CZ (MEE) 9353 ISBN 0 580 34126 7 Co-operating
3、organizations The Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Admiralty Air Ministry Associated Offices Technical Co
4、mmittee Association of Consulting Engineers (Incorporated) British Chemical Plant Manufacturers Association British Compressed Air Society British Electrical and Allied Manufacturers Association British Engineers Association British Gear Manufacturers Association British Internal Combustion Engine M
5、anufacturers Association British Iron and Steel Federation British Railways, The British Transport Commission Crown Agents for Oversea Governments and Administrations D.S.I.R. National Engineering Laboratory Electricity Council, the Generating Board and the Area Boards in England and Wales Engineeri
6、ng Equipment Users Association Gas Council High Commission of India Institute of Marine Engineers Institute of Petroleum Institution of Civil Engineers Institution of Gas Engineers Institution of Heating and Ventilating Engineers Institution of Mechanical Engineers Institution of Mechanical Engineer
7、s (Automobile Division) Institution of Production Engineers Locomotive and Allied Manufacturers Association of Great Britain Machine Tool Trades Association Ministry of Labour (Factory Inspectorate) Ministry of Power Ministry of Transport Ministry of Works National Coal Board National Physical Labor
8、atory (D.S.I.R.) Radio Industry Council War Office Amendments issued since publication Amd. No. Date of issue Comments 1957 April 1976 Indicated by a sideline in the marginBS1790:1961 BSI 01-2000 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Nomenclature and d
9、efinitions 1 Section 1. Length bars 3 General design 3 4 Material 3 5 Hardening and stabilizing 6 6 Finish 6 7 Accuracy 6 8 Connecting screws for inspection and workshop bars 11 9 Marking 11 10 Case 12 11 Protection against climatic conditions 12 Section 2. Accessories for use with inspection and wo
10、rkshop length bars 12 Material 13 13 Method of attachment 13 14 Base 13 15 Large radiused jaw 13 16 Small plane-faced jaw 14 17 Spherical end piece 14 18 Screws 15 19 Case 15 20 Protection against climatic conditions 15 Appendix A Recommended sets of inspection and workshop grades of length bars 16
11、Appendix B Details of published papers on screwed connections 17 Figure 1 Exaggerated illustration of flatness tolerance 2 Figure 2 Exaggerated illustration of parallelism tolerance 2 Figure 3 Exaggerated illustration of squareness tolerance 2 Figure 4 Indication of airy positions 3 Figure 5 Referen
12、ce or calibration grade length bar 4 Figure 6 Inspection grade length bar 4 Figure 7 Workshop grade length bar 5 Figure 8 New design of threaded connection for length bars 5 Figure 9 Original type of screwed connection for length bars 6 Figure 10 Assembly of accessories 12 Figure 11 Base 13 Figure 1
13、2 Large radiused jaw 14 Figure 13 Small plane-faced jaw 14 Figure 14 Spherical end piece 15 Table 1 Reference grade length bars 8 Table 3 Calibration grade length bars 9 Table 5 Inspection grade length bars 10 Table 7 Workshop grade length bars 11 Table 9 Inspection grade bars 16 Table 11 Workshop g
14、rade bars 17BS1790:1961 ii BSI 01-2000 Foreword This Standard makes reference to the following British Standards: BS 84, Parallel screw threads of Whitworth form. BS 1133, Packaging Code Section 6: Temporary prevention of corrosion of metal surfaces (during transportation and storage) Section 19: Us
15、e of desiccants in packaging. This revised British Standard for length bars has been prepared under the authority of the Mechanical Engineering Industry Standards Committee in response to a request received from the National Physical Laboratory. It forms one of a series of standards for engineers pr
16、ecision measuring tools which has been prepared with the co-operation of the manufacturers and in close collaboration with the National Physical Laboratory. From experience gained since its original publication in1952, and having regard to research work carried out at the National Physical Laborator
17、y which has resulted in the introduction of a refined screwed connection 1)for length bars, it has been considered desirable to revise this Standard. The more important features of this revision are as follows: i) A new calibration grade of bar has been introduced into the standard so that four grad
18、es of accuracy are now provided, viz., reference, calibration, inspection and workshop. The basis of the respective tolerances on length for these grades of bars follows closely that of the corresponding grades for slip (or block) gauges laid down in BS888. ii) Modern end measuring machines are now
19、provided with universally adjustable supports; in consequence, the squareness tolerance between the measuring faces of a bar and the common axis of its Airy positions has been relaxed and an enlarged uniform tolerance has been assigned to all grades of bars. This has led to the elimination of the ra
20、ised Airy bands specified for the original types of reference and inspection bars; the Airy positions on all grades of bars are now indicated by pairs of circumferential lines scribed round the bar. iii) The opportunity has also been taken to rationalize the requirements for accessories by standardi
21、zing one type only. iv) The refined screwed connection referred to above has been introduced into the Standard. By means of this connection the change in the length of a built-up combination of bars, arising from stresses set up at each joint during hand assembly, has been reduced to about one micro
22、 inch (0.000 001in) per joint. The original screwed connection designed for use with workshop grade bars and their associated accessories is quite satisfactory for workshop accuracy and has therefore been retained in the revised Standard. By employing the refined connection, however, it is now possi
23、ble to build bars of higher grade accuracy into a combination without any appreciable loss of overall inherent accuracy and this facility has accordingly been extended to inspection grade bars. It is essential that the refined joint be employed on all inspection grade bars, but for workshop grade ba
24、rs the choice of screwed connection, refined or original type, is optional. 1) For details of the refinement in the design of the screwed connection see references to published papers given inAppendix B of this Standard.BS1790:1961 BSI 01-2000 iii The improved type of screwed connection is the subje
25、ct of a patent No.819921 by The Department of Scientific and Industrial Research. The British Standards Institution has been assured by D.S.I.R. that licenses to manufacture the connections will be granted to approved intending manufacturers on reasonable conditions. A British Standard does not purp
26、ort 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. Summary of pages This document comprises a front cover, an inside front c
27、over, pagesi toiv, pages1to18, 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 indicated in the amendment table on the inside front cover.iv blankBS1790:1961 BSI 01-2000 1 1 Scope This British Standard
28、relates to length bars of the cylindrical type, in inch sizes up to48in, having parallel end faces finished by lapping. If longer bars are required, they shall be uniform in diameter and straight overall to the limits laid down in Clauses7 a) and b); tolerances for flatness and parallelism of faces
29、shall be proportionate to those specified in the appropriateTable 1, Table 3, Table 5 and Table 7, and their lengths shall conform to the requirements of Clause7 d)ii). Provision is made for two designs of length bar, one with complete plane faces and the other with annular faces surrounding an inte
30、rnally threaded hole at one end or both ends of the bar. Section 1 provides for four grades of accuracy, namely: i) Reference ii) Calibration iii) Inspection iv) Workshop. Reference grade bars, as their name implies, are intended for use as reference standards. They have completely plane faces and e
31、mbody the highest order of accuracy as regards both their end faces and the finishing of their actual lengths to their nominal sizes. It is recommended that they should be supplied with a certificate by the National Physical Laboratory which confirms their full accordance with this British Standard
32、and gives the deviations from their nominal lengths to an appropriately high order of accuracy. To derive the maximum benefit from these very high grade reference bars they should be used only in standards rooms which are temperature controlled at68 1 F (20 1 / 2 C) and with comparators of suitably
33、high sensitivity. Calibration grade bars possess the same degree of perfection in their completely plane end faces as the reference grade bars. They differ only in the somewhat wider tolerances allowed in the adjustment of their lengths to the nominal sizes, which thus permits them to be produced mo
34、re economically than reference grade bars. It is recommended, however, that calibration grade bars should, like those of reference grade, be supplied and used with a N.P.L. certificate giving the actual deviation in the length of each bar from its nominal size. NOTEThe wider tolerances permitted on
35、the lengths of calibration grade bars render them no less serviceable than reference grade bars when used as standards for the accurate measurement of other bars. As already mentioned for reference grade bars, calibration grade bars require to be used under suitable conditions of temperature and wit
36、h appropriate comparators if the fullest advantage is to be gained of the very high accuracy associated with their certified sizes. Inspection grade bars have internally threaded ends and can thus be used in combination with each other. They are intended for use in inspection rooms and tool rooms. W
37、orkshop grade bars also have internally threaded ends and can be used with slip gauges, comparators and their own accessories for measuring gauges, jigs, work pieces, etc. As their name implies, they are intended for use in workshops. General dimensions, tolerances on length and standards of accurac
38、y for flatness, parallelism and squareness of faces are specified for all grades of bars. Section 2 relates to the essential features of design and accuracy of accessories for use with inspection and workshop grade bars. Recommended sets of inspection and workshop grade bars and the sources of paper
39、s on the refined type of screwed connection are given in Appendices. 2 Nomenclature and definitions For the purpose of this standard the following definitions apply. 2.1 airy positions the Airy positions are those points at which a bar of uniform cross section must be supported, when used with its a
40、xis horizontal, to bring the end faces of the bar parallel; when it is so supported, the flexure of the bar under its own weight is reduced almost to a minimum (seeFigure 5) 2.2 Length 2.2.1 reference and calibration bars the length of a reference or calibration grade bar is defined as the distance
41、from the centre of one of its faces to a flat surface in wringing contact with the opposite face, measured normal to the surface and at a temperature of 68 F (20 C) NOTETo reduce possible effects of small permissible errors in the flatness of the faces of a bar, the length should be measured first w
42、ith one face and then the other wrung to the flat surface and the mean of the two results taken.BS1790:1961 2 BSI 01-2000 2.2.2 inspection and workshop bars the length of an inspection or a workshop grade bar is defined as the mean of four measurements made parallel to the axis of the bar at quadran
43、tal positions, and at the mean radius of its annular faces. These measurements are made at a temperature of 68 F (20 C) if the bars are measured in a horizontal position they should be supported at the Airy positions described in Sub-clause2.1 2.3 flatness tolerance the maximum permissible distance
44、between two imaginary parallel planes within which the contour of a face can just be enclosed (seeFigure 1) 2.4 parallelism tolerance parallelism in this context is intended to refer to the maximum variation in the length of any one bar (seeFigure 2) 2.5 squareness tolerance the maximum permissible
45、distance between two imaginary parallel planes normal to the axis of the Airy positions and just enclosing the face under consideration (seeFigure 3) Figure 1 Exaggerated illustration of flatness tolerance Figure 2 Exaggerated illustration of parallelism tolerance Figure 3 Exaggerated illustration o
46、f squareness toleranceBS1790:1961 BSI 01-2000 3 Section 1. Length bars 3 General design a) Reference grade and calibration grade bars (seeFigure 5). Reference and calibration grade bars shall take the form of cylindrical bars 7 / 8inch in diameter and shall have completely plane end faces. The Airy
47、positions on all bars6 inches in length and over shall be indicated by two symmetrically spaced pairs of bold circumferential lines scribed around the bars, as shown inFigure 4. The lines shall not stand proud of the surface of the bar. b) Inspection grade and workshop grade bars (seeFigure 6 andFig
48、ure 7). Inspection grade and workshop grade bars shall take the form of cylindrical bars 7 / 8inch in diameter, internally threaded and recessed at one or both ends. It may be convenient to supply on occasion the1in bar solid throughout. The Airy positions on all bars6 inches in length and over shal
49、l be indicated as for reference and calibration grade bars. The threaded connections at the end of inspection bars shall be made in accordance with the dimensions and tolerances specified inFigure 8(a). Those at the ends of workshop bars shall preferably be made in accordance with the dimensions and tolerances specified inFigure 9(a); alternatively they may be made to the dimensions and tolerances given inFigure 8(a). All threaded connections shall be assembled hand tight only. NOTE 1Bars screwed togethe
