The Essential Guide to Technical Product Specification: Engineering Drawing. Colin Simmons and Neil Phelps

Transcription

1 The Essential Guide to Technical Product Specification: Engineering Drawing Colin Simmons and Neil Phelps

2 irst published in the UK in 2009 by BSI 389 Chiswick High Road London W4 4AL British Standards Institution 2009 All rights reserved. Except as permitted under the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, photocopying, recording or otherwise without prior permission in writing from the publisher. Whilst every care has been taken in developing and compiling this publication, BSI accepts no liability for any loss or damage caused, arising directly or indirectly in connection with reliance on its contents except to the extent that such liability may not be excluded in law. While every effort has been made to trace all copyright holders, anyone claiming copyright should get in touch with the BSI at the above address. BSI has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this book, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. The right of Colin Simmons and Neil Phelps to be identified as the authors of this Work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act Typeset in Optima and Gill Sans by Monolith Printed in Great Britain by Berforts Group, Stevenage British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN

3 v Contents Introduction vii Dimensioning and tolerancing of size Introduction General principles Types of dimension Dimensioning conventions Arrangement of dimensions Methods for dimensioning common features Dimensioning screw threads and threaded parts Dimensioning chamfers and countersinks Equally spaced repeated features Dimensioning of curved profiles Dimensioning of keyways Tolerancing Interpretations of limits of size for a feature-of-size Datum surfaces and functional requirements Relevant standards 21 Geometric tolerancing datums and datum systems Introduction Terms and definitions Basic concepts Symbols Tolerance frame Toleranced features Tolerance zones Datums and datum systems Supplementary indications Examples of geometrical tolerancing Relevant standards 114 Graphical symbols for the indication of surface texture Introduction The basic graphical symbol Expanded graphical symbols Mandatory positions for the indication of surface texture requirements Surface texture parameters Indication of special surface texture characteristics Indications on drawings Relevant standards 123

4 vi The Essential Guide to Technical Product Specification: Engineering Drawing Welding, brazed and soldered joints Symbolic representation Introduction Relevant standards 133 Limits and fits Introduction Selected ISO fits Hole basis Selected ISO fits Shaft basis Methods of specifying required fits Relevant standards 140 Metric screw threads Introduction Thread designation Relevant standards 168 Illustrated index to BS Normative references 169

5 vii Introduction This guide has been produced as a companion to BS 8888, presenting up-to-date information based on the technical product specification aspects of BS 8888 and the essential standards it references. Its aim is to offer straightforward guidance together with pictorial representations, to all practitioners of technical product specification, i.e. those currently using BS 8888 and those who, in a bid to conform to global ISO practices, are making or wish to make, the transition from the old BS 308 to BS Its scope is to provide the necessary tools to enable engineers engaged in design specification, manufacturing and verification with the essential basic information required for specifying a product or component. It includes comprehensive sections extracted from and referenced to international standards relating to linear, geometric and surface texture dimensioning and tolerancing, together with the practice of welding symbology, limits and fits and thread data. It also includes an illustrated index to all standards referenced in BS This guide does not replace BS 8888 which is the definitive standard for technical product realization. Any element of BS 8888 not included in this guide should not be considered as less important to technical specification than those included. Most of the drawings in this guide have been extracted (and adapted) from the following BSI publications: BS EN ISO 1101, BS EN ISO 1302, BS ISO 5459, BS 8888 and PP 8888, Parts 1 and 2.

6 1 Chapter 1 Dimensioning and tolerancing of size 1.1 Introduction Dimensioning is the process of applying measurements to a technical drawing. It is crucial to the whole process by which the designer will communicate the information required for the manufacture and verification of products. 1.2 General principles Dimensions shall be applied to the drawing accurately, clearly and unambiguously. The following points shall be regarded as general dimensioning principles to be applied to all technical drawings. Each dimension necessary for the definition of the finished product shall be shown once only. Never calculate a dimension from the other dimensions shown on the drawing, nor scale the drawing. There shall be no more dimensions than are necessary to completely define the product. Preferred sizes shall be used whenever possible (see notes). Linear dimensions shall be expressed in millimetres (unit symbol mm ). If this information is stated on the drawing, the unit symbol mm may be omitted. If other units are used, the symbols shall be shown with their respective values. Dimensions shall be expressed to the least number of significant figures, e.g. 45 not 45,0. The decimal marker shall be a bold comma, given a full letter space and placed on the baseline. Where four or more numerals are to the left or right of the decimal marker, a full space shall divide each group of three numerals, counting from the position of the decimal marker, e.g. 400 or 100 but (see notes). A zero shall precede a decimal of less than one, e.g. 0,5. An angular dimension shall be expressed in degrees and minutes, e.g. 20 and or, alternatively, as a decimal, e.g. 30,5. A full space shall be left between the degree symbol and the minute numeral. When an angle is less than one degree, it shall be preceded by a zero, e.g NOTES: Preferred sizes are those referring to standard material stock sizes and standard components such as nuts, bolts, studs and screws. Decimal marker points or commas are not used to separate groups of numerals. This causes ambiguity since the decimal marker is denoted by a comma.

7 N N N 2 The Essential Guide to Technical Product Specification: Engineering Drawing 1.3 Types of dimension or a configuration nee processing (for example, a product from a foundry or forge) or the purposes of this section, the following definitions apply. further processing. dimension numerical value expressed in appropriate units of measurement and indicated graphically on technical drawings with lines, symbols and notes Dimensions are classified according to the following types. 6. Dimensioning of technical drawings functional dimension dimension that is essential to the function of the piece or space ( in igure 1). See also 1.14 non-functional dimension dimension that is not essential to the function of the piece or space ( N in igure 1) End product: complete part ready for assembly or service, or a configuration produced auxiliary dimension from a drawing specification. An end product may also be a part ready for further Dimension, given processing for information (for example, purposes a product only, from that adoes foundry not or govern forge) production or a configuration or inspection needing operations and is derived from other values shown on the drawing or in related documents further processing. NOTE: An auxiliary dimension is given in parentheses and no tolerance may be applied to it ( AUX in igure 1). N feature individual characteristic such as a flat surface, 6. Dimensioning a cylindrical surface, of technical two parallel drawings surfaces, a shoulder, a screw thread, a slot or a profile end product complete part ready for assembly or service or configuration produced from a drawing specification ct: complete part or ready for assembly or service, or a configuration Design requirement produced End product: complete part ready for assembly or service, or a configuration prod from a drawing specification. An end product may also be a part ready for fu Design requirement part ready for further processing (for example, a product from a foundry (b) or Shoulder forge) or screw a configuration wing specification. An end product may also be a part ready for further needing further processing (for example, a product from a foundry or forge) or a configuration needing cessing. N N N (AUX) igure 57: Types of dimensioning igure 57: Types of dimensioning Design requirement Design requirement (b) Shoulder (b) screw Shoulder screw (c) Threaded(c) hole Threaded hole N N N (AUX) N igure 1 Types of dimensioning

8 Dimensioning and tolerancing of size Dimensioning conventions Technical product specification standards specify the following conventions when dimensioning drawings. Extension lines shall normally be placed outside the view to aid clarity, as shown in igure 2. The extension line connects the dimension line (on which the value of the measurement is placed) to the reference points on the outline of the drawing. The following standard practice is specified. Crossing of extension lines shall be avoided whenever possible. There should be a small gap between the outline of the drawing and a projection line. The extension line shall extend slightly beyond the dimension line, as shown in igure 2. Extension lines shall, where possible, be drawn at right angles to the dimension line. Centre-lines, extensions of centre-lines and continuations of outlines shall never be used as Drawing dimension practice lines. They may, however, be used as projection lines. Arrowheads and origin circles are commonly used as terminators for dimension lines. Oblique strokes and points can also be used, as shown in igures 3 and 4. Dimension lines shall be unbroken even if the feature they refer to is shown as interrupted, as illustrated in igure 5. Leader line Dimensioning 6. Dimensioning of technical of technical ofdrawings technical draw Dimensioning Extension of technical of line technical of technical drawings drawings Value of the dimension 1500 ] When ] When symmetrical ] symmetrical Whenparts symmetrical parts are drawn areparts drawn arepartially, drawn the portions partially, the portions of the the portions of dimension the dimension of the lines dimension lines lines Origin indication Dimension line Termination (arrowhead) extend extend a short aextend short way way beyond a short beyond the wayaxis the beyond axis of of thesymmetry axis of andsymmetry the second the second andtermination thetermination secondistermination is ] When ] When ] When symmetrical symmetrical parts parts are parts drawn are drawn are partially, drawn partially, the partially, portions the portions theof portions the the ofdimension the dimension lines lines lines igure 58: omitted, Examples omitted, as shown of omitted, asextension igure shown in igure as 2 inlines shown igure Examples 62. andin62. dimension igure of extension 62. lines lines and dimension lines extend extend a short extend a short waya short way beyond beyond waythe beyond axis the of axis the symmetry of axis symmetry of symmetry and the andsecond the andsecond the second termination termination is is is omitted, omitted, as omitted, shown as shown as in shown igure in igure 62. in igure Terminators: dimension lines shall be terminated according to one of the representations igure shown igure 59: in igure Terminators 59: igure Terminators 3. 59: for Terminato for 6.4 Dimensioning conventions igure igure 59: igure Terminators 59: Terminators 59: Terminators for for fo Arrowhead, Arrowhead, closed Arrowhead, closed closed(b) Arrowhead, (b) Arrowhead, (b) closed Arrowhead, closed closed (c) Arrowhead, (c) Arrowhead, (c) open Arrowhead, open open 30 dimension dimension dimension lines lines lines and filled and filled 30 (BS and filled (BS (BS Arrowhead, closed and filled 30 (b) Arrowhead, closed 30 Arrowhead, Arrowhead, Arrowhead, closed closed closed (b) Arrowhead, (b) Arrowhead, (b) Arrowhead, closed closed closed (c) Arrowhead, (c) Arrowhead, (c) (c) Arrowhead, open Arrowhead, open 30 open 30 open default) (BS 8888 default) default) default) General and filled and filled 30 and(bs filled (BS (BS default) default) default) Technical product specification standards recommend the following conventions (d) Arrowhead, open 90 (BS when 8888 dimensioning (e) Oblique drawings. stroke (f) Point (used only if no place for (d) Arrowhead, (d) Arrowhead, (d) open Arrowhead, open open(e) 90 Oblique stroke (f) Point (used only if no non-preferred) (e) Oblique (e) stroke Oblique stroke (f) Point arrowhead; (used (f) Point only(used if the no oblique only if no stroke may (BS 8888 (BS 8888 (BS non-preferred) 8888 non-preferred) place place for arrowhead; foralso arrowhead; place be for used the arrowhead; the BS 8888) the (d) Arrowhead, (d) Arrowhead, (d) Arrowhead, open open 90 open (e) Oblique (e) Oblique (e) stroke Oblique stroke stroke (f) oblique Point oblique (f) Point stroke (used (f) stroke Point only oblique may(used if only also nostroke ifalso only may if noalso (BS 8888 (BS 8888 (BS 8888 non-preferred) Extension lines and dimension lines igure 3 Terminators for dimension place be used be place forused arrowhead; place BS lines for 8888) be arrowhead; BS for used 8888) arrowhead; the BSthe 8888) the oblique oblique stroke oblique maystroke also also may also The extension line connects the dimension be used beline used be BS (on used 8888) BS which 8888) BSthe 8888) value of the measurement is placed) to the reference points on the outline of the drawing. The following standard practice is recommended. igure igure : Origin : igure Origin: Origin indication indication indication igure igure : igure Origin : Origin : Origin ] Extension lines (continuous narrow line type , see Table 1) should normally indication indication indication be placed outside of the view to aid clarity, as shown in igure 58. ] Crossing of extension lines should be avoided whenever possible. igure igure 61: Dimensioning 61: igure Dimensioning 61: Dimension ] There should be a small gap between the outline of the drawing interrupted and a projection interrupted features interrupted features features line. The extension line should extend slightly beyond the dimension igure igure 61: line, igure 61: as shown 61: Dimensioning dimension dimension linesdimension lines

9 dimension lines Arrowhead, closed (b) Arrowhead, closed (c) Arrowhead, open 30 (d) andarrowhead, filled 30 (BS open (e) 30 Oblique stroke (f) Point (used only if no 4 (BS default) 8888 non-preferred) The Essential Guide to Technical Product place Specification: for arrowhead; Engineering the Drawing oblique stroke may also be used BS 8888) Origin indication: (d) Arrowhead, the origin open of 90 the dimension (e) Oblique line shall stroke be indicated as (f) shown Point (used in igure only if4. no (BS 8888 non-preferred) place for arrowhead; the oblique stroke may also be used BS 8888) igure : Origin indication igure 4 Origin indication igure : Origin igure 61: Dimensioning indication interrupted features igure 61: Dimensioning interrupted features igure 5 Dimensioning interrupted features igure 62: Dimension lines on a partial view of a When symmetrical parts are drawn partially, the portions of the dimension lines shall extend a short way symmetrical part beyond the axis of symmetry and the second termination shall be omitted, as shown in igure 6. igure 62: Dimension lines on a partial view of a symmetrical part igure 6 Dimension lines on a partial view of a symmetrical part Arrangement of dimensions 69 The way in which dimensions are typically used on drawings is shown in igure 7. Conventions for arranging dimensions on drawings are as follows. Dimensions shall be placed in the middle of the dimension line above and clear of it. Dimensions shall not be crossed or separated by other lines on the drawing. Values of angular dimensions shall be oriented so that they can be read from the bottom or the right-hand side of the drawing, as shown in igure 8. Where space is limited, the dimension can be placed centrally, above, or in line with, the extension of one of the dimension lines, as shown in igure 9. Larger dimensions shall be placed outside smaller dimensions, as shown in igure 10.

10 igure 63: Examples of the ways in which dimensions are typically used on drawings ] Where space is limited, the dimension can be placed centrally, above, or in line with, the extension of one of the dimension lines (see igure 66). ] Larger dimensions are placed outside smaller dimensions (see igure 67). Dimensioning and tolerancing of size 6. Dimensioning of technical5drawings ] Dimensions of diameters should be placed on the view that provides the greatest clarity (see igure 68). Dimensions of diameters shall be placed on the view that provides the greatest clarity, as shown in igure 11. igure 64: Orientation of linear dimensions Dimensioning of technical drawings 30 igure 7 Examples of the ways in which dimensions are typically used on drawings igure 64: Orientation of linear dimensions 30 igure 65: Orientation of angular dimensions Drawing practice Drawing practice igure 66: Dimensioning igure 66: Dimensioning smaller features smaller features 30 (b) igure 8 Orientation of linear and angular dimensions 3 6 igure 30 65: 3 Orientation of 3 angular dimensions igure 9 Dimensioning smaller features igure 67: Larger igure 67: Larger dimensions placed outside dimensions placed outside smaller dimensions smaller dimensions (b) igure 68: Dimensions of igure 68: Dimensions of diameters placed on view diameters placed on 30 view providing the greatest providing the greatest clarity clarity 30 igure 10 Larger dimensions placed outside smaller dimensions 71 (b)

11 Dimensioning of technical drawings 6 The Essential Guide to Technical Product Specification: Engineering 6. Drawing Dimensioning of tech re 68: Dimensions of eters placed on view viding the greatest ity igure 69: Parallel dimensioning igure 6 dimensio igure 11 Dimensions of diameters placed on view providing greatest clarity Superimposed running dimensioning is a simplified parallel dimensioning and may Dimensioning 6.6 from Examples a common feature of can dimensioning be used where a number methods of dimensions of the same direction relate to a common be used where origin. there are space limitations. The common origin is shown as in igure 70. Superimposed running dimensioning is a simplified parallel dimensioning and may Dimensioning Dimension from values a common may be: be feature used where may there be executed are space as limitations. parallel dimensioning The common or origin as superimposed is shown as in igure 70. running dimensioning. Dimensioning from a common feature is used where a number of dimensions of the Dimension values may be: Parallel ] same dimensioning above direction and clear is relate the of placement tothe a common dimension of a origin. number line 6. (seedimensioning of igure single 70a); dimension or of lines technical parallel drawings to one another and spaced ] out inso line that with the the dimensional corresponding value extension can easily line be (see added igure in, 70b). as shown in igure 12a. ] above and clear of the dimension line (see igure 70a); or Superimposed running dimensioning is a simplified parallel dimensioning and may be used where Dimensioning from a common feature may be executed as parallel dimensioning or as there are space limitations. The common ] in lineorigin with is the as corresponding shown igure extension 12. Dimension line (see values igure 70b). may be above and clear of superimposed the dimension running line, as dimensioning. shown in igure 12b; or in line with the corresponding extension line, as shown in igure 12c. igure 70: Examples of Parallel dimensioning is the placement of a number of single dimension lines parallel running dimensioning to one another and spaced out so that the dimensional value canigure easily69: be Parallel added in igure 7 dimensioning running (see igure 69) a) b) Superimposed running dimensioning is a simplified parallel dimensioning and may be used where there are space limitations. The common origin is shown as in igure 70. Dimension values may be: ] above and clear of the dimension line (see igure 70a); or ] in line with the corresponding extension line (see igure 70b) c) (b) (b) igure 12 Parallel dimensioning and running dimensioning igure 70: Examples of running dimensioning 73

12 Drawing practice Chain dimensioning consists of a chain of dimensions. These should only be used where the possible accumulation of tolerances does not affect the function of the part Dimensioning (see and igure tolerancing 71). of size 7 Chain dimensioning consists of a chain of dimensions. These should only be used Combined dimensioning uses chain dimensioning and parallel dimensioning on the where the possible accumulation of tolerances does not affect the function of the part Chain dimensioning same Chain drawing dimensioning consists (see of igure a chain consists 72). (see igure 71). of of dimensions. a chain ofthese dimensions. shall only These be should used where only be the used possible accumulation where of tolerances the possible does accumulation not affect the offunction tolerances of does the part, not affect as shown the function in igure of 13. the part igure 71: Chain dimensioning igure 71: Chain dimensioning igure 71: Chain dimensioning igure 72: Examples of Combined (see iguredimensioning 71). uses chain dimensioning and parallel dimensioning on the same drawing (see igure 72). Combined dimensioning uses chain dimensioning and parallel dimensioning on the same drawing (see igure 72) igure 13 Chain dimensioning combined dimensioning Combined dimensioning uses chain dimensioning and parallel dimensioning on the same drawing view. igure 14a illustrates combining single 1dimensions 70 and parallel 200 dimensioning 30 from a common feature. igure 14b illustrates combining single dimensions and chain dimensions. igure 72: Examples of combined dimensioning igure 72: Examples of combined dimensioning Combining single dimensions and parallel dimensioning from a common feature Combining single dimensions and parallel dimensioning from a common feature Combining single dimensions a) and parallel dimensioning from a common feature (b) Combining single dimensions and chain dimensions 74 (b) Combining single dimensions and chain b) dimensions igure 14 Combined dimensioning (b) Combining single dimensions and chain dimensions 74 74

13 Dimensioning by coordinates uses superimposed running dimensioning in two directions at right angles, as shown The Essential in igure Guide 73. to The Technical common Product originspecification: may be any suitable Engineering Drawing 8 Dimensioning by coordinates uses superimposed running dimensioning in two directions at right angles, as shown in igure 73. The common origin may be any suitable common reference feature. It may be useful, instead of dimensioning as shown in igure 73, to tabulate dimensional values as shown in igure 74. common reference feature. It may be useful, instead of dimensioning as shown in Dimensioning by coordinates uses superimposed running dimensioning in two directions at right angles, igure 73, to tabulate dimensional values as shown in igure 74. as shown in igure 15a. The common origin may be any suitable common reference feature. It may be useful, instead of dimensioning as shown in igure 15a, to tabulate dimensional values as shown in igure 73: Dimensioning igure 15b. by coordinates (two igure directions) 73: Dimensioning 1 by coordinates (two directions) ,5 15, ,5 15, ,5 15, ,5 13,5 13,5 13, ,5 13,5 13,5 13, a) in two directions Y Y A2 A2 A1 A1 X B2 B2 B1 B1 C C igure 74: Dimensioning by coordinates (tabulated) igure 74: Dimensioning by coordinates (tabulated) X b) tabulated igure 15 Dimensioning by coordinates 75 75

14 S 20 A diameter of a circle or cylinder is dimensioned by prefixing the value with the symbol Ø. This symbol should be as large as the following numerals and the slanting line should be about Dimensioning 30 clockwiseand from tolerancing the vertical, of size in the direction in which it is to be read (see igure 68). It has already been pointed out (see igure 68) that the dimensions should be placed on the view that most clearly shows the information. 1.6 Methods for dimensioning common features Where dimension lines and other lines (e.g. extension lines) would otherwise intersect, the dimension Certain lines tofeatures, the feature such can as diameters, be dimensioned radii, squares, by leader hole lines sizes, as shown chamfers, countersinks and counter-bores, in igure 75. Where can occur the frequently whole viewin is engineering not shown, drawings. concentric diameters can be A diameter of a circle or cylinder shall be dimensioned by prefixing the value with the symbol Ø, dimensioned as in igure 76. as shown in igure 16. A square feature shall be dimensioned by prefixing the value with the symbol. Additionally, square and flat features can be indicated by continuous narrow lines drawn diagonally on Circles are to be dimensioned as shown in igure 77 and spherical surfaces as shown in the flat feature, as shown in igure 18. igure 78. Where dimension lines and other lines (e.g. extension lines) would otherwise intersect, the dimension lines to the feature can be dimensioned by leader lines as shown in igure 16. Where the whole view is not shown, concentric diameters shall be dimensioned as in igure Dimensionin Dimensionin R igure 78: Radial values R igure 16 Diameter dimensions indicated by leader lines igure 17 Dimensioning concentric diameters on a partial view igure 79: Square values 40 NOTE. Leader line should be in line with centre of circle 40 igure 18 Dimensioning a square Circles shall be dimensioned as shown in igure 19 and spherical surfaces as shown in igure 20. igure 80: Spherical radi Radii of features shall be dimensioned by prefixing the value with the letter R. Radii shall be values dimensioned by a line that passes through, or is in line with, the centre of the arc. The dimension line shall have one arrowhead only, which shall touch the arc. S 50 Radii that require their centres to be located shall be dimensioned as in igure 21a; those that do not shall be dimensioned as in igure 21b. Spherical radii shall be dimensioned as shown in igures 21c and 21d. SR12 SR

15 370 Drawing practice 10 The Essential Guide to Technical Product Specification: Engineering Drawing Drawing practice Drawing practice Drawing practice 20 igure 77: Dimensioning S 50a S 50 igure circle spherical Radii Radii Radii of features are dimensioned by prefixing the value with the letter R. Radii should Radii of features are dimensioned by prefixing the value with the letter R. Radii should NOTE. Leader line should be dimensioned 6.7.3by Radii a line that passes through, or is in line with, the centre of the arc. be in line with centre be dimensioned 6.7.3by Radii a line that passes through, or is in line with, the centre of the arc. of circle The dimension line should have one arrowhead only, which should touch the arc. The dimension Radiiline of features should have are dimensioned arrowhead S 20 by prefixing only, S which the 20 value shouldwith touch the the letter arc. R. Radii should Radii that require Radii of features are dimensioned by prefixing the value with the letter R. Radii should be dimensioned their centres by ato line bethat located passes should through, be dimensioned or is in with, as in igure the centre 79a; of the arc. Radii that require a) (b) b) be dimensioned their centres by ato line be that located passes should through, be dimensioned or is in lineas with, in igure the centre (b) 79a; those that of the arc. do not dimension are dimensioned line should as in have igure one79b. arrowhead Spherical only, radii which are dimensioned should touch asthe arc. those that do Thenot dimension are dimensioned line should as inhave igure one79b. arrowhead igure Spherical 20 only, radii Dimensioning which are dimensioned should touch as shown in igures 79c and 79d. the arc. shown in igures Radii that 79crequire and 79d. their centres to be located spherical should be diameters dimensioned as in igure 79a; Radii that require their centres to be located should be dimensioned as in igure 79a; igure 19 Dimensioning those that a diameter do not are dimensioned as in igure 79b. Spherical radii are dimensioned as those Holes that aredo to not be dimensioned are Holes dimensioned are to be as shown dimensioned as in igure in igure 79b. as shown 79. Spherical Theindepth igure radii of79. the are The dimensioned drilled depth hole ofwhen the as drilled hole w shown in igures and 79d. shown given in igures note given in note form refers to the depth of the cylindrical portion of the hole and n S 50 form 79crefers and 79d. to the depth ofigure the cylindrical 78: Dimensioning portion of the hole and not to the extremity made the extremity by the point made of R5,5 the by the drill, spherical point unless diameters of otherwise drill, unless specified. R4 otherwise specified. R5,5 R4 R4 R4 R8 S 20 R8 R8 R8 (b) oles are to be dimensioned as shown in igure a) 79. The depth of the drilled (b) hole when b) iven in note form refers to the depth of the cylindrical portion of the hole and not to e extremity made by the point of the drill, unless otherwise specified. (b) (b) R2 R2 (b) 40 R2 R2 R5,5 R5,5 R100 R100 R25 R25 R4 R4 R100 R100 SR12 SR12 R25 R25 R4 R4 SR20 SR SR SR 77 SR12 SR12 (c) (c) SR20 SR SR SR SR SR (c) c) (d) d) (c) (d) igure 79: Dimensioning radii igure 79: Dimensioning radii igure 79: Dimensioning radii igure 79: Dimensioning radii igure 21 Dimensioning radii (d) (d) SR SR 78 78

16 Holes Holes are dimensioned are dimensioned as shown as shown in igure in igure 80. The 80. depth The depth of theof drilled the drilled hole, hole, when when given given after the after diameter, the diameter, refers refers to theto depth the depth of theof cylindrical the cylindrical portion portion of theof hole theand hole and not tonot theto extremity the extremity made made by theby point the point of theof drill, theunless drill, unless otherwise otherwise specified. specified. Dimensioning and tolerancing of size , igure igure 80: Dimensioning 80: Dimensioning Holes 7 7 holes holes 9,5 9, Teacher s note: the method of production (e.g. drill, punch, bore or ream) sh Holes shall be dimensioned as shown in igure 22. The depth of the drilled hole, when given after the diameter, refers Holesto are the dimensioned depth of the as cylindrical shown inot portion igure be specified 80. of the Theexcept hole depthwhere and ofnot theit to drilled is essential the extremity hole, to when the function of the drawing made by the point of the given drill, after unless theotherwise diameter, specified. refers to the depth of the cylindrical portion of the hole and The method not toof the production extremity(e.g. madedrill, by the punch, pointbore of the or drill, ream) unless shall otherwise not be specified specified. except where it is essential to the function of the part. + 0,02 + 0, Chords, 32 arcs 0 32 and 0 angles 4 5 igure 80: Dimensioning The dimensioning of chords, 7arcs and angles should beholes as shown in igure 81 9,5 18 Teacher s Teacher s note: note: the method the method of production of production (e.g. drill, (e.g. punch, drill, punch, bore bore ream) or ream) should should Drawing practice 38 not benot specified be specified except except where where it is essential it is essential to theto function the function of theof drawing. the drawing , , , Chords, Chords, arcs arcs and angles and angles igure 22 Dimensioning holes The dimensioning The dimensioning of chords, of chords, arcs and arcsangles and angles should should be ascurved be shown shown in igure in igure Chord surfaces (b) Arc Teacher s note: the method of production (e.g. drill, punch, bore or ream) should The dimensioning of chords, arcs and angles shall be as shown in igure 23. not be specified except where When it is essential dimensioning to the the function spacing of of theholes drawing. and other features on a curved surf whether the 105 dimensions 105 are chordal or igure circumferential, igure 81: 42 Dimensioning 81: Dimensioning they are to be indicated cle on the drawing, as shown in igure 82. chords, chords, arcs and arcs angles and angles + 0,02 tice Chords, arcs and angles igure 82: Dimensions on 800 OUTER SURACE The a curved dimensioning surface of chords, arcs and angles should be as shown in igure 81. Chord Chord (b) Arc(b) Arc (c) Angle a) chord b) arc c) angle igure Dimensioning chords, arcs and 105angles igure 81: Dimensioning chords, arcs and angles Dimensioning the spacing of holes and other features on a curved surface shall be as shown in igure 24, whether the dimensions are chordal or circumferential, they shall be indicated clearly on the drawing Curved surfaces When dimensioning the spacing Chord of holes and other features on a(b) curved Arc surface, whether the dimensions are chordal (c) Angle (c) orangle circumferential, they are to be indicated clearly on the drawing, as shown in igure sions on 800 OUTER SURACE (c) Angle ,5 - igure 24 Dimensions on a curved surface 6.8 Dimensioning screw threads and threade parts

17 12 The Essential Guide Thread to Technical Product Specification: 6. Dimensioning Engineering Drawing of technical drawing 6. system Dimensioning 6. and Dimensioning size of technical of technical drawings drawings 6. Dimensioning 6. of technical of technical drawings drawings The letter M, denoting ISO metric screw threads, is followed by the values of th 1.7 Dimensioning screw threads and threaded parts ISO metric screw threads shall be designated in accordance with BS EN ISO , which specifies that Thread the designation Thread system shall system and Thread indicate size and system the size and size thread system, Thread nominal tolerance diameter and class the thread tolerance class. If Thread Thread system system and and size size necessary, the pitch shall also be indicated; however, when designating metric coarse threads, the pitch The letter M, denoting ISO metric screw threads, is followed by the values of the Theis letter generally TheM, letter denoting omitted. M, denoting ISO metric ISO screw metricthreads, screwor threads, isgeneral followed isuse, followed bythe thetolerance values by of values class the 6H of is the suitable for internal threads and toleranc The letter The letter M, M, denoting ISO metric screw threads, is followed by the values of the The nominal nominal denoting diameter diameter ISO metric refers to and screw the major pitch (if threads, diameter required), is followed of with a multiplication by the values and internal threads; sign of the between the dimension them, nominal nominal diameter diameter and pitch and(if pitch required), (if required), with aclass multiplication with6g a for multiplication external sign threads. between sign between The them, thread them, tolerance class is preceded by a hyphen, e.g nominal nominal diameter diameter and pitch (if required), with a multiplication sign between them, relating to the depth e.g. of M8 and thread pitch 1. (if required), with a multiplication sign between them, e.g. M8 e.g. 1. M8 1. refers to the full M10-6H depth or of M10 thread. The 1-6g. direction of a right hand thread (RH) is not e.g. generally M8 e.g. M8 1. noted; 1. however left hand threads shall be denoted with the abbreviation LH after the thread designation Thread tolerancescrew classthreads are dimensioned as shown in igures 83 and Thread Thread tolerance tolerance class class Thread system Thread Thread and tolerance size tolerance class class The letter M, denoting or general ISO metric use, the screw tolerance threads, class shall 6Hbe is followed suitable for by internal the values threads of the and nominal tolerance or general or general use, theuse, tolerance the tolerance class 6Hclass is suitable 6H is suitable for internal for internal threads threads and tolerance and tolerance diameter and or pitch general or (if required), general use, use, with the a tolerance multiplication class 6H sign is between suitable them, for internal e.g. M8 threads 1. and tolerance class the 6g tolerance for external class threads. 6H is suitable The thread for tolerance internal threads class is and preceded tolerance by a hyphen, e.g. class 6gclass for external 6g for external threads. threads. The thread Thetolerance thread tolerance class is preceded class is preceded by a hyphen, by a hyphen, e.g. e.g. class 6g class for6g external for external threads. The thread tolerance class is preceded by a hyphen, e.g. M10-6H threads. or M10 The thread 1-6g. tolerance class is preceded by a hyphen, e.g. M10-6H Thread M10-6H or tolerance or M10 1-6g. class 1-6g min M10-6H M10-6H or M10 or M10 1-6g. 1-6g. or general use, the tolerance class 6H is suitable for internal threads and tolerance class 6g for external full thread threads. The Screw tolerance threads class are dimensioned shall be preceded as shown by a in hyphen, igures e.g. 83 and M10-6H 84. Screw threads Screw threads are dimensioned are dimensioned as shown as in shown igures in igures 83 and and 84. or M10 1-6g. Screw Screw threads threads are dimensioned are dimensioned as shown as shown in igures in igures 83 and and 84. Screw threads shall be dimensioned as shown in igures 25 and 26. M36-6g M36-6g M36-6g M36-6g M36-6g nominal diameter and pitch (if required), with a multiplication sign between them e.g. M8 1. M36-6g 38 max 30 min igure 83: Dimensioning 30 min 30 min igure 83: (b) igure Dimensioning 83: Dimensioning 30 min30 minfull thread igure igure 83: Dimensioning 83: external Dimensioning screw threads full thread full thread external external screw threads screw threads full thread full thread external external screw screw threads threads M20-6g M20-6g M20-6g M12-6H x max 38 max max min 38 max38 max (b) full thread a) (b) (b) b) (b) (b) igure 25 Dimensioning external screw threads M20-6g M20-6g M12 x 1,25-6H 16 M20-6g M12-6H x 16 M12-6H M12-6H x 16 x 16 M12-6H x 1516min 15 min M12-6H 15 min x min full thread full thread 15 full min thread full thread full thread (b) igure 84: Dimensioning igure 84: igure Dimensioning 84: Dimensioning M12 x 1,25-6H M12 x 1,25-6H M12 x 1,25-6H igure igure 84: Dimensioning 84: internal Dimensioning screw threads M12 x M12 1,25-6H x 1,25-6H internal screw internal threads screw threads internal internal screw screw threads threads M6-6H x 10 (b) 20 min full thread a) (b) (b) b) (b) 28 max c) (b) including run-out (c) igure 26 Dimensioning internal screw threads (c) M6-6H x 10 M6-6H x M6-6H 10 x 10 M6-6H x 20 min full thread 20 min full M6-6H 20 thread min x full 10thread 20 min full 28 max including run-out 28 max including min max full including run-out threadrun-out 28 max 28 including max (c) including run-out run-out (c) (c) (c)

18 The use of reference letters in conjunction with an explanatory note or table can also be 45, the indications may be simplified as shown in igures 104 and 105. Note. Methods of production (e.g. drill, punch, bore, ream ) should not be + 0, specified, except where they are essential to the function. Dimensioning and tolerancing of size Chamfers and countersinks 1.8 Dimensioning chamfers and countersinks 9, igure 13103: Chamfer dimensioning Chamfers should be dimensioned as shown in igure 103. Where 38 the chamfer angle is Chamfers shall be dimensioned as shown in igure 27. Where the chamfer angle is 45, the indications 45, the indications may be simplified as shown in igures 104 and 105. may be simplified as shown in igure igure 104: 45 chamfer + 0,02 32 simplified 0 igure 103: Chamfer 2 or or or Chamfers and countersinks , igure 102: Hole dimensioning dimensioning Chamfers should be dimensioned as shown in igure 103. Where the chamfer angle is 45, the indications may be simplified as shown in igures 104 and or or or igure 105: Dimensionin igure 104: 45 chamfer internal chamfers simplified igure 103: Chamfer dimensioning igure 27 Dimensioning external and internal chamfers or igure 105: Dimensionin internal igure 104: chamfers 45 chamfer simplified Engineering drawing practice or 2 45 igure 28 Simplified dimensioning of chamfers igure 105: Dimensionin 2 45 internal chamfers Countersinks are dimensioned by showing either the required diametral dimension 2 45 at Countersinks shall be dimensioned by showing either the required diametral dimension at the included the included angle, or the depth and the included or angle 113(see igure 106). angle, or the depth and the included angle, as shown in igure 29. igure 106: Dimensioning countersinks or ,5 igure 29 Dimensioning countersinks 13.8 Other indications

19 13.5 Equally spaced repeated features 14 The Essential Guide to Technical Product Specification: Engineering Drawing 13.5 Equally spaced repeated features Where repeated features are linearly spaced, a simplified method of dimensioning may be used, as illustrated in igure Equally spaced repeated features If Where thererepeated is any ambiguity, features areone linearly feature spaced, space a simplified may be dimensioned method of dimensioning as illustrated may in Where repeated igure be used, features 96. as illustrated are linearly igure spaced, 95. a simplified method of dimensioning may be used, as shown in igure 30. If there is any ambiguity, one feature space may be dimensioned as illustrated in re 95: Dimensioning igure 96. near spacings 50 re 95: Dimensioning near spacings (= 90) igure 30 Dimensioning of linear spacings (= 90) re 96: Dimensioning near spacings If tothere avoid is any ambiguity, one feature space may be dimensioned as illustrated in igure 31. fusion re 96: Dimensioning near spacings to avoid fusion (= 306) 18 Angular, 15 equally spaced features may 17 be 18 dimensioned (= 306) as illustrated in igure Dimensioning from a common feature The angles igure of 31 the spacings Dimensioning may be omitted of linear when spacings the intent to avoid is evident, confusion as shown in igure Angular, 98. equally spaced features may be dimensioned as illustrated in igure 97. Angular, equally Circular The angles spaced spaced offeatures the features spacings shall may may be be dimensioned be dimensioned omitted when as indirectly shown the intent by igure specifying is evident, 32. The theas angle number shown of of the in spacings can be omitted common igure where 98. the intent is explicit, as shown in igure 33. features, as illustrated in igure 99. Circular spaced features may be dimensioned indirectly by specifying the number of common features, as illustrated in igure 99. igure 97: Dimensioning of angular spacings ' ' (52 30') igure 32 Dimensioning angular spacing 50 igure 98: The omission of angles of spacings to avoid confusion 4 9

20 15 Dimensioning and tolerancing of size 10 30' ' (52 30') igure 97: Dimensioning of angular spacings ' ' (52 30') igure 98: The omission angles of spacings to avo confusion 50 igure 98: The omission angles of spacings to avo confusion 4 9 igure 33 Omission of angle 5 of spacing 16 igure 99: Dimensioning circular spacings Circular spaced features can be dimensioned 6 indirectly by specifying the number of common features as shown in igure igure 99: Dimensioning circular spacings igure 34 Dimensioning circular spacings 111

21 16 The Essential Guide to Technical Product Specification: Engineering Drawing Series or patterned features of the same size may be dimensioned as illustrated in Series iguresor 100 patterned and 101. features of the same size may be dimensioned as illustrated in Series or patterned igures 100 features and of 101. the same size may be dimensioned as illustrated in igures 35 and 36. re 100: Defining a ntity of elements of the re 100: Defining a e size: linear ntity of elements of the e size: linear igure 35 Dimensioning a quantity of features of the same size linear re 101: Defining a ntity of elements of the re 101: Defining a e size: circular ntity of elements of the e size: circular Holes 13.6 Holes igure 36 Dimensioning a quantity of features of the same size circular Holes are dimensioned as shown in igure 102. The depth of the drilled hole, when 1.10 Dimensioning given after the diameter, of curved shallprofiles Holes are dimensioned as shown refer intoigure the depth 102. The of the depth cylindrical of theportion drilled hole, of thewhen hole given and not after to the diameter, extremity made shall refer by the to the point depth of the of drill, the cylindrical unless otherwise portion specified. Curved profiles composed of circular arcs shall be dimensioned by radii, as shown of in the igure hole 37. Coordinates and not locating to thepoints extremity on a made curved by surface, the pointas ofshown the drill, in igure unless otherwise 38, shall only specified. be used when the profile is not composed of circular arcs. The more coordinates specified, the better the uniformity of the curve

22 12.9. Curved profiles composed of circular arcs should be dimensioned by radii, as illustrated Dimensioning and tolerancing of size in igure igure 118: The dimensioning of a curved profile Engineering drawing practice igure 37 Dimensioning of a curved profile igure 119: Linear coordinates of a series of points through which a profile passes 119 igure 38 Linear coordinates of a series of points through which a profile passes Coordinates locating points on a curved surface, as illustrated in igure 119, should 1.11 Dimensioning of keyways only be used when the profile is not composed of circular arcs. The more coordinates Keyways in hubs or shafts specified, shall the be better dimensioned the uniformity by one of of the the curve. methods shown in igure 39. NOTE: urther information on keys and keyways is given in BS , Specification for metric keys and keyways Part 1: Parallel and taper keys and igure BS , 120 illustrates Specification a method for metric of keys specifying and keyways a cam Part profile 2: Woodruff in association keys and keyways. with a follower. The follower is indicated by a long-dashed double-dotted narrow line type (see Table 1). igure 120: Specifying dimensions in association with a follower 0 b

23 shown in igure 5. NOTE urther information on keys and keyways is given in BS , Specification for metric keys and keyways Part 1: Parallel and taper keys, and BS , Specification for metric keys and keyways 18 Part 2: Woodruff keys The and Essential keyways. Guide to Technical Product Specification: Engineering Drawing igure 5 Dimensioning of keyways a) Parallel hub b) Tapered keyway in parallel hub c) Parallel keyway in tapered hub d) Parallel shaft e) Parallel keyway in tapered shaft f) Parallel shaft g) Tapered shaft igure 39 Dimensioning of keyways 1.12 Tolerancing BSI Tolerancing is the practice of specifying the upper and lower limit for any permissible variation in the finished manufactured size of a feature. The difference between these limits is known as the tolerance for that dimension. All dimensions (except auxiliary dimensions) are subject to tolerances. Tolerances shall be specified for all dimensions that affect the functioning or interchange ability of the part. Tolerances shall also be used to indicate where unusually wide variations are permissible. Tolerances shall be applied either to individual dimensions or by a general note giving uniform or graded tolerances to classes of dimensions, for example: TOLERANCE UNLESS OTHERWISE STATED LINEAR ±0,4 ANGULAR ±0 30 The method shown in igure 40a should be followed where it is required to tolerance individual linear dimensions. This method directly specifies both the limits of the size of the dimension, the tolerance being the difference between the limits of the size. The larger limit of the size shall be placed above the smaller limit and both shall be given to the same number of decimal places. The method shown in igure 40b can be used as an alternative way of specifying tolerances.

24 6.9.3 Tolerancing of individual linear dimensions The method shown in igure 85 is recommended where it is required to tolerance individual linear Dimensioning dimensions. and This tolerancing methodof directly size specifies both the limits of the size of the6. Dimensioning of technical 19 drawin dimension, the tolerance being the difference between the limits of the size. ce by size 32,15 31, ,15-0,20 The larger limit of the size is placed above the smaller limit, and both are given to the same number of decimal a) places. b) igure 40 Linear dimension tolerance by directly specifying limits of size Tolerancing of individual angular dimensions The methods The shown methods in igure shown41 in igure may be 86used may be to used tolerance tolerance individual individual angular angular dimensions. igure 86: Tolerancing 30 30' 30 0' 90 ± 0 30' 0 30,5 ± 0,1 angular dimensions (b) (c) a) b) c) 6.10 Summary igure 41 Tolerancing angular dimensions 1.13 Interpretations of limits of size for a feature-of-size This chapter has covered those parts of the standards that deal with dimensioning and tolerancing which are likely to be of use to Design and Technology teachers and their Limits of size for an individual feature-of-size shall be interpreted according to the principles and rules students in schools and colleges. The key points are as follows. defined in BS ISO 8015, BS EN ISO and BS EN ISO A feature-of-size BIP 2155 may consist of two parallel plane surfaces, a cylindrical surface or a spherical ile name: _40b.e surface, in each ] The case general defined principles with a of linear dimensioning size. A feature-of-size as set out in may BS 8888:2006 also consist should of two always plane surfaces at an angle to each be followed other (a ifwedge) effectiveor communication a conical surface, between in each thecase designer, defined manufacturer with angular and size. BS ISO 8015 endstates user that is tolimits be established of size control and maintained. only the actual local sizes (two-point measurements) of a feature-of-size and not its deviations of form (e.g. the roundness and straightness deviations of a ] unctional dimensions are those that directly affect the function of the product. cylindrical feature, or the flatness deviations of two parallel plane surfaces). orm deviations may be ] controlled by individually All dimensions specified except geometrical auxiliary dimensions tolerances, are general subject to geometrical tolerancing. tolerances or through the use of the ] envelope The decimal requirement marker is represented (where the maximum by a comma material not a point. limit of size defines an envelope of perfect form ] for Groups the relevant of numerals surfaces; to the see left BS and ISO right 8015). of the decimal marker should be divided BS ISO 8015 up defines into groups the principle of three, counting of independency, from the decimal according marker, to which and a each full space, specified not dimensional a and geometrical requirement on a drawing is met independently, unless a particular relationship is comma, left between them. specified. A relationship may be specified through the use of the envelope requirement or material condition modifiers maximum material condition (MMC) or least material condition (LMC). Where no relationship is specified, any geometrical tolerance applied to the feature-of-size applies regardless of feature size, and the two requirements shall be treated as unrelated, as shown in igure 42. Relevant standards Title The limits of size do not control the form, orientation, or the spatial relationship between, individual features-of-size. BS EN ISO 16 Technical drawings Dimensioning and Consequently, if a particular relationship tolerancing of size and of profiles form, or size and location, or size and orientation is required, it needs to be specified. BS ISO Technical drawings Indication of dimensions and tolerances Part 1: General principles

25 BS 8888:2008 BritiSh Standard 20 The Essential Guide to Technical Product Specification: Engineering Drawing igure 3 Permissible interpretations when no form control is given on the drawing 25,0 24,9 a) drawing presentation a b c NOTE There is no form control (i.e. over roundness, straightness or cylindricity). Measurements a, b and c may lie between 25.0 mm and 24.9 mm, meeting the drawing requirement using two-point measurement only. b) Permissible interpretation: straightness unconstrained 25,0 Maximum size Maximum roundness deviation (resulting from a lobed form) NOTE or any cross-section of the cylinder, there is no roundness control. c) Permissible interpretation: roundness unconstrained igure 42 Permissible interpretations when no form control is given on the drawing Limits of size with mutual dependency of size and form COMMENTARY AND RECOMMENDATIONS ON Limits of size with mutual dependency of size and form Some national standards apply, or have applied, the Envelope Requirement to all features-of-size by default. As the Envelope Some national standards apply, or have Requirement applied, has the been envelope the default, requirement they have to all not features-of-size used a symbol by to indicate this requirement; rather they use a note to indicate when this default. As the envelope requirement has been the default, they have not used a symbol to indicate this is not required. This system of tolerancing is sometimes described as the requirement; rather they use a note Principle to indicate of Dependency, when this is or not the required. application This of system the Taylor of tolerancing Principle. is sometimes described as the principle Standards of dependency, which apply, or the or application have applied, of the the Envelope Taylor principle. Requirement by Standards which apply, or have default applied, include: the envelope requirement by default include: ASME Y14.5 (the requirement that there is an envelope of perfect ASME Y14.5 form corresponding to the Maximum Material Size of the feature is The requirement that there shall be an envelope defined as of Rule perfect #1). form corresponding to the maximum material size of the feature is defined as BS Rule 308 #1). (the Principle of Dependency was taken as the default option under BS 308, although the option of working to the BS 308 Principle of Independency was included, through the use of The principle of dependency was taken as the the BS default 308 triangle option I indication): under BS 308, although the option of working BS 8888 I to the principle of independency was included, through the use of the BS 308 triangle I indication. BS 8888 prior to the 2004 revision (the Principle of Dependency was taken BS as 8888the default I option under BS 8888:2000 and BS 8888:2002, although the option of working to the Principle of Independency was included, through the use of the BS 8888 triangle I indication). 16 BSI 2008

26 Dimensioning and tolerancing of size 21 BS 8888 Prior to the 2004 revision; the principle of dependency was taken as the default option under BS 8888:2000 and BS 8888:2002, although the option of working to the principle of independency was included, through the use of the BS 8888 triangle I indication. BS 8888:2004 and BS 8888:2006 the principle of dependency could be explicitly invoked through the use of the BS 8888 triangle D indication. BS 8888 D As the interaction between the envelope requirement and individual geometrical tolerances is not always fully defined within the ISO system, and as the application of the envelope requirement by default to all features-of-size is not formally supported within the ISO system, the use of the principle of dependency is no longer recommended Datum surfaces and functional requirements unctional dimensions shall be expressed directly on the drawing, as shown in igure 1. The application of this principle will result in the selection of reference features on the basis of the function of the product and the method of locating it in any assembly of which it may form a part. If any reference feature other than one based on the function of the product is used, finer tolerances will be necessary to meet the functional requirement, which in turn will increase the cost of producing the product, as shown in igure 43 on page Relevant standards BS EN ISO 16, Technical drawings Dimensioning and tolerancing of profiles BS ISO 129-1, Technical drawings Indication of dimensions and tolerances Part 1: General principles BS ISO 3040, Technical drawings Dimensioning and tolerancing Cones BS ISO 10579, Technical drawings Dimensioning and tolerancing Non-rigid parts BS ISO 406, Technical drawings Tolerancing of linear and angular dimensions BS EN , General tolerances Part 1: Tolerances for linear and angular dimensions without individual tolerance indications BS , Specification for metric keys and keyways Part 1: Parallel and taper keys BS , Specification for metric keys and keyways Part 2: Woodruff keys and keyways BS ISO 8015, Technical drawings undamental tolerancing principle BS EN ISO 146-1, Geometrical Product Specifications (GPS) Geometrical features Part 1: General terms and definitions BS EN ISO 146-2, Geometrical Product Specifications (GPS) Geometrical features Part 2: Extracted median line of a cylinder and a cone, extracted median surface, local size of an extracted feature PP , Engineering drawing practice: a guide for further and higher education to BS 8888:2006, Technical product specification (TPS)

27 BIP 2155 ile name: _43c.eps 22 The Essential Guide to Technical Product Specification: Engineering Drawing Description a) Assembly drawing showing a given functional requirement, namely the limits of height of the top face of item 1 above the top face of item 3, with a tolerance of 0.08 mm b) Detail of head of item 1 showing given limits of size, with a tolerance of 0.03 mm c) Item 2 dimensioned from a functional reference surface NOTE: One direct dimension with a tolerance of 0.05 mm is needed to satisfy the condition shown in a). A nominal flange thickness of 5 mm has been assumed. This value is non-functional and can have BIP any 2155 large tolerance. d) Item 2 dimensioned from a nonfunctional reference surface NOTE: Tolerances have had to be reduced; two dimensions with tolerances of, say, 0.02 mm for the flange and 0.03 mm are now needed to satisfy the condition shown in a). BIP 2155 Drawing 3 5,5 5,0 5,00 4, ,00 17,97 correct functional reference surface incorrect non-functional reference surface igure 43 Effect on tolerances by changing datum surfaces from those determined by functional requirements 1 12,00 11,92 6,05 6,00 ile name: _43a.eps 11,03 11,00 ile name: _43b.eps BSI/PM: Jenny Cranwell Date: 15/06/2009 Modifications: BSI/PM: Jenny Cranwell Date: Approval 15/06/2009 of issue Modifications: Ap Date: 15/06/2009 Modifications: Approval of issue