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1、BRITISH STANDARD Confirmed September 1992 BS 308-2: 1985 Reprinted, incorporating Amendments No. 1, 2 and 3 Engineering drawing practice Part 2: Recommendations for dimensioning and tolerancing of size UDC 741.05:62:003.63 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:07:01 GMT+00:00 200
2、6, Uncontrolled Copy, (c) BSI BS 308-2:1985 This British Standard, having been prepared under the direction of the General Mechanical Engineering Standards Committee was published under the authority of the Board of BSI and comes into effect on 31 October BSI 10-1998 First published September 1927 F
3、irst revision December 1943 Second revision December 1953 Third revision November 1964 Fourth revision October 1972 Fifth revision October 1985 The following BSI references relate to the work on this standard: Committee reference GME/4 Draft for comment 83/70209 DC ISBN 0 580 14651 0 Committees resp
4、onsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Committee (GME/-) to Technical Committee GME/4 upon which the following bodies were represented: Amalgamated Union of Engineering Workers (Technical and Supervisor
5、y Section) British Internal Combustion Engine Manufacturers Association British Paper and Board Industry Federation British Railways Board British Standards Society British Telecommunications Drawing Office Material Manufacturers and Dealers Association Electricity Supply Industry in England and Wal
6、es Electronic Engineering Association Engineering Equipment and Materials Users Association Federation of Manufacturers of Construction Equipment and Cranes Gauge and Tool Makers Association Institution of Electronic and Radio Engineers Institution of Engineering Designers Institution of Mechanical
7、Engineers Institution of Production Engineers Ministry of Defence Post Office Society of British Aerospace Companies Limited Telecommunication Engineering and Manufacturing Association United Kingdom Atomic Energy Authority Amendments issued since publication Amd. No.Date of issueComments 6711April
8、1991 7157September 1992 8744October 1995Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:07:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 308-2:1985 BSI 10-1998i Contents Page Committees responsibleInside front cover Forewordiv 1Scope1 2Definitions1
9、3Principles of dimensioning1 4Method of application (general conventions)3 5Arrangement of dimensions and application of values7 6Dimensioning methods11 7Methods of dimensioning common features14 8Toleranced dimensions26 9Interpretation of toleranced centre distances29 10Dimensioning and tolerancing
10、 of tapered features29 11Interpretations of limits of size for the control of form37 12Completeness of drawings in respect of tolerances37 13Machining and surface texture indication38 14Marking43 Appendix A Aspects of engineering drawing practice covered by British and international (ISO) standards4
11、4 Index45 Figure 1 Application of dimensions to suit functional requirements2 Figure 2 Effect of changing datum surfaces from those determined by functional requirements3 Figure 3 Elements of dimensioning4 Figure 4 Projection lines from points of intersection4 Figure 5 Projection lines perpendicular
12、 to required dimensions5 Figure 6 Projection lines oblique to feature5 Figure 7 Chord6 Figure 8 Arc6 Figure 9 Angles6 Figure 10 Dimensioning interrupted features6 Figure 11 Dimension lines on partial view of a symmetrical part6 Figure 12 Dimensioning where space is restricted7 Figure 13 Dimensioning
13、 using oblique strokes where space is restricted7 Figure 14 Use of letters and symbols with dimensions8 Figure 15 Orientation of linear dimensions8 Figure 16 Orientation of angular dimensions9 Figure 17 Position of dimensions9 Figure 18 Offset dimension9 Figure 19 Arrangement of dimensions to avoid
14、congestion10 Figure 20 Use of an extension to a dimension line10 Figure 21 Dimension at end of leader line terminating at a surface10 Figure 22 Dimensioning small features10 Figure 23 Larger dimensions placed outside smaller dimensions10 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:07:0
15、1 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 308-2:1985 ii BSI 10-1998 Page Figure 24 Indication of a feature not drawn to scale 10 Figure 25 Overall length added as an auxiliary dimension 10 Figure 26 Application of auxiliary dimensions 11 Figure 27 Dimensions repeated to avoid long and intersec
16、ting leaders 11 Figure 28 Notes and symbols used to avoid long and intersecting leaders 11 Figure 29 Parallel dimensioning 12 Figure 30 Superimposed running dimension12 Figure 31 Chain dimensioning 12 Figure 32 Combined dimensioning 13 Figure 33 Dimensioning by coordinates 13 Figure 34 Dimensioning
17、by coordinates and a table 14 Figure 35 Dimensions of diameters placed on the most appropriate view for clarity 14 Figure 36 Dimensions related to features by leader lines 15 Figure 37 Dimensioning concentric diameters on partial views 15 Figure 38 Dimensioning circles 15 Figure 39 Spherical diamete
18、rs 16 Figure 40 Dimensioning radii of arcs 16 Figure 41 Locating inconveniently placed centres 16 Figure 42 Indicating radii by other dimensions 16 Figure 43 Spherical radius 17 Figure 44 Dimensioning curved lines by means of radii 17 Figure 45 Dimensioning of curved lines by means of coordinates 18
19、 Figure 46 Dimensioning holes 18 Figure 47 Dimensioning hole positions on a circle by angular spacing 19 Figure 48 Dimensioning hole positions by centre distances or coordinates 19 Figure 49 Dimensioning on curved surfaces 20 Figure 50 Dimensioning of equally-spaced features 20 Figure 51 Dimensionin
20、g of equally-spaced features emphasising spacing 20 Figure 52 Dimensioning of equally-spaced features on an arc 21 Figure 53 Omission of dimensions where spacings are self-evident 21 Figure 54 Locating equally-spaced features by number required 21 Figure 55 Dimensioning repeated features 22 Figure 5
21、6 Chamfers at 45 22 Figure 57 Chamfers at angles other than 45 22 Figure 58 Dimensioning of countersinks 23 Figure 59 Dimensioning of counterbores 23 Figure 60 Dimensioning of spotfaces 23 Figure 61 Dimensioning a special screw thread 24 Figure 62 Dimensioning to end of full thread 24 Figure 63 Dime
22、nsioning to end of full thread and to limit of thread run-out 24 Figure 64 Dimensioning threaded holes 25 Figure 65 Dimensioning keyways 26 Figure 66 Limits of size specified directly 26 Figure 67 Specifying a size with limits of tolerance 27 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03
23、:07:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 308-2:1985 BSI 10-1998iii Page Figure 68 Tolerancing angular dimensions 27 Figure 69 Interpretation of angular tolerances 28 Figure 70 Examples of general tolerance notes 28 Figure 71 Comparison of chain and parallel methods of dimensioning using
24、toleranced centre distances 31 Figure 72 An interpretation of toleranced centre distances 31 Figure 73 Dimensioning positions by toleranced centre distances 32 Figure 74 Dimensions and symbol 32 Figure 75 Tolerancing a tapered object by the basic taper (or angle) method 32 Figure 76 Tolerancing a ta
25、pered object by the basic taper (or angle) method using a datum distance 33 Figure 77 Tolerancing a tapered object by the basic taper (or angle) method using a datum diameter 33 Figure 78 Basic taper (or angle) method of tolerancing gradual or slow internal tapers 34 Figure 79 Basic taper (or angle)
26、 method of tolerancing components where tapered features need clearance on assembly 34 Figure 80 Basic taper (or angle) method of tolerancing a fast taper 34 Figure 81 Basic taper (or angle) method of tolerancing mating tapers that determine longitudinal location 35 Figure 82 Tolerancing tapered obj
27、ects where the rate of taper is more important than size or location 35 Figure 83 Defining a taper by reference to a gauge 36 Figure 84 Alternative methods of tolerancing a tapered object where the location of a datum diameter is more important than the taper 36 Figure 85 Defining a taper by referen
28、ce to its mating component 36 Figure 86 Interpretation of limits of size with dependency of size and form 38 Figure 87 Interpretations using the principle of independency for a cylindrical component which has tolerances of size only given on the drawing 39 Figure 88 Surface texture symbols 39 Figure
29、 89 Application of basic surface texture symbols 40 Figure 90 Indication of allowable surface texture 40 Figure 91 Application of surface texture values 40 Figure 92 Application of surface texture values by reference letters and listed values 41 Figure 93 Machining not permitted 41 Figure 94 Positio
30、ns for specifying additional characteristics 41 Figure 95 Supplementary surface texture characteristics and finishes 42 Figure 96 Indication of sampling length 42 Figure 97 Direction of lay 42 Figure 98 Method of identifying independency system of tolerancing 43 Table 1 Symbols for the direction of
31、lay 43 Publications referred to 50 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:07:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 308-2:1985 iv BSI 10-1998 Foreword This revision of BS 308-2 has been prepared under the direction of the General Mechanical Engineering Standards Committe
32、e; it reflects the established conventions and also takes account of both national and international developments since the 1972 revision, which is now withdrawn. The proven record of standards applied to engineering drawing now enables its recognition as the graphical language of communication in e
33、ngineering both nationally and internationally. Drawings made to the accepted standards in one country, when based on standards published by the International Organization for Standardization (ISO), are understood and can be used around the world in virtually all countries. With this in mind it was
34、recognized and accepted to be important as a policy for this revision that particular attention and care should be paid to the quality of content of both text and figures to ensure their clarity and ease of understanding. The UK continues to participate actively in ISO Technical Committees on techni
35、cal drawing for the establishment of international published standards and much of the contents of this standard reflects those agreements reached internationally with which the UK has concurred. Some notes appear in this standard to draw attention to occasional divergence of practice. Appendix A pr
36、ovides information on aspects of engineering drawing practice covered by British and international standards. The recommendations of this standard have been established having regard to the requirements of microfilming. Drawings prepared in accordance with this standard should be suitable for microf
37、ilming and reduced-size reproduction techniques. During the course of this revision particular attention has been paid to developments in computer aided machine draughting and it has been established that such machines are currently capable of complying with this standard. Any minor exceptions due t
38、o the limitations of a particular system would not be expected to prejudice the understanding of a drawing otherwise claimed to comply with this standard. The 1972 revision was coincidentally undertaken during the main period of transition of UK industry to the metric system and a limited recognitio
39、n of the imperial system of units was included but this has not been retained in the present revision. In the ISO committee for technical drawing it is the intention to unify, in one set of standards, the practices and conventions of all disciplines using technical drawings and their standards curre
40、ntly attempt to reflect that policy. In the UK the traditional separations are maintained and it should be carefully noted that BS 308 continues to provide recommendations for engineering drawings in the manufacturing industries associated with mechanical, electrical, electronics, hydraulics, pneuma
41、tics and nuclear engineering disciplines, as previously. The requirements of the building, architectural, civil and structural engineering and construction services industries continue to be covered by BS 1192. BS 308 does not cover special disciplines such as in naval architecture and aeronautical
42、lofting. There are standards published for some industries using BS 308 as a basis but requiring additional recommendations and conventions particular to the discipline. BS 4301, which gives recommendations for the preparation of drawings for optical elements and systems, and BS 2774, which gives dr
43、awing conventions for laboratory glassware, are examples. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:07:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 308-2:1985 BSI 10-1998v BS 5070, dealing with engineering diagram drawing practice, is a companion standard to BS 308 and caters for
44、 the same industries, providing recommendations on a wide variety of engineering diagrams. Commonly, as a diagram can be called a “drawing” and a drawing can be called a “diagram”, it is useful to summarize the difference in the scopes of these standards. BS 308 covers what are commonly accepted to
45、be drawings that define shape, size and form. BS 5070 covers the drawing of diagrams that are normally associated with flow of one sort or another and which relate components (usually indicated by symbols) functionally one to another by the use of lines, but do not depict their shape, size or form;
46、neither do they in general indicate actual connections or locations. For convenience of use, this revision of BS 308 follows the precedent established in 1972 of publishing in three Parts. This Part leads on from Part 1, which deals with general principles, and continues the development of the drawi
47、ng with the application of dimensions and tolerances and other related information on size and finish. It also covers interpretations and tolerancing principles. The recommendations are generally in accordance with the following international standards. ISO 129-1985, Engineering drawing Dimensioning
48、. ISO 406-1982, Technical drawings Linear and angular tolerancing Indications on drawings. ISO 1302-1978, Technical drawings Method of indicating surface texture on drawings. BS 308-3 deals specifically with geometrical tolerancing. Particular attention is drawn to the revision of the clause on inte
49、rpretation of limits of size (clause 9 of BS 308-2:1972). This now appears as clause 11 where, together with a clarification of the traditional interpretation, a new tolerancing concept has been introduced, in which specified dimensional and geometrical requirements are met independently (see 11.3). This principle of independency, as it is known, has been developed inter