Technical product specification (TPS) Specification

Transcription

1 Incorporating Corrigendum No. 1 BRITISH STANDARD Technical product specification (TPS) Specification ICS ; NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW

2 Publishing and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2006 ISBN The following BSI references relate to the work on this standard: Committee reference TDW/4 Draft for comment 06/ DC Publication history First published August 2000 Second edition October 2002 Third edition October 2004 Fourth edition October 2006 Amendments issued since publication Amd. no. Date Text affected December 2006 Clarification of figures in Annex A and Annex E.

3 Contents Foreword iii 1 Scope 1 2 References 1 3 Terms and definitions 2 4 Global standards underpinning BS Expression of the concept 5 6 Types of documentation 6 7 Scales 8 8 Lines, arrows and terminators 9 9 Lettering 9 10 Projections Views Sections Symbols and abbreviations Representation of features Representation of components Dimensioning and tolerancing Geometrical tolerancing Surface texture indication Graphical representation and annotation of 3-D data (3-D modelling output) Security Storage and retrieval Marking Protection notices 27 Annexes Annex A (normative) Normative references 28 Annex B (informative) Informative references 51 Annex C (normative) Document security Enhanced 52 Annex D (informative) Key differences between BS 8888 geometrical tolerancing and ASME Y14.5 geometric dimensioning and tolerancing (GD&T) 53 Annex E (informative) BS ISO 1101:1984 to BS ISO 1101:2004 The evolution 57 Annex F (informative) Technical product specification Geometrical product specification (GPS) 69 Annex G (informative) Technical product realization UK development 79 Annex H (informative) Index of choices and defaults for BS 8888: List of figures Figure 1 Metric reference graduations 8 Figure 2 Auxiliary view showing true shape of inclined surface 11 Figure 3 Interpretations using the principle of independency for a cylindrical component for which a tolerance of size only is given on the drawing 17 Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 88, an inside back cover and a back cover. BSI 2006 i

4 ii BSI 2006 Figure 4 Interpretation of limits of size with dependency of size and form 19 Figure 5 Dimensioning of keyways 21 Figure 6 Examples of general tolerance notes 22 Figure 7 Method of indicating that the independency system of tolerancing has been used 26 Figure 8 Method of indicating that the dependency system of tolerancing has been used 26 Figure E.1 Indication of orientation of the tolerance zone 58 Figure E.2 Use of the median feature 59 Figure E.3 Restricted parts of a feature 60 Figure E.4 Example of a common tolerance zone 60 Figure E.5 Example of a common tolerance zone 61 Figure E.6 Examples of the use of the all around symbol 61 Figure E.7 Unequally disposed tolerance zone indicator 62 Figure E.8 Example of the use of the compound toleranced feature 63 Figure E.9 Indicating the start and end of the compound toleranced feature 63 Figure E.10 Indicating a common set of toleranced features 64 Figure E.11 Indicating a common compound tolerance zone 64 Figure E.12 Two different ways of indicating a GPS with projected tolerance modifier 66 Figure E.13 Explanation of the direction of the extended feature 66 Figure E.14 Example of direct indication of a projected tolerance with an offset 66 Figure E.15 Example of indirect indication of a projected tolerance with an offset 67 Figure E.16 Example of the use of projected tolerance zone together with the median modifier 68 Figure E.17 Example of the use of projected tolerance zone together with a common zone modifier 68 Figure F.1 Model of the relationship between specification, verification and the actual workpiece 70 Figure F.2 The link between design intent and metrology 71 Figure F.3 The duality principle 73 Figure F.4 The GPS matrix model 78 Figure G.1 The relationship between the elements of a technical drawing 81 Figure G.2 Schematic of the TPR triumvirate 83 Figure G.3 Technical product realization 83 List of tables Table A.1 Normative references 28 Table B.1 Informative references 51

5 Foreword Publishing information This British Standard was published by BSI and came into effect on 31 October It was prepared by Technical Committee TDW/4, Technical product specification (TPS) Methodology, presentation and verification. A list of organizations represented on this committee can be obtained on request to its secretary. Supersession This British Standard supersedes BS 8888:2004, which is withdrawn. This fourth revision updates and extends the third edition, bringing in relevant standards published during 2005 and the first few months of This revision has been made with particular reference to online provision. Relationship with other publications The function of BS 8888 is to draw together, in an easily accessible manner, the full complement of International Standards relevant to the preparation of technical product specifications, in accordance with geometrical product specification (GPS) principles. However, it is not the intention that BS 8888 should be a stand-alone standard since it is part of a triumvirate of TPR (Technical Product Realization) standards comprising BS 8887 and BS The relationship of these three standards to each other is explained in Annex G. It should be noted that BS 8888 has recently been taken up by the Ministry of Defence as part of its DEF-STAN for defence project specification and that BSI does make educational/training aids available in this field and is currently planning a major education/training initiative which, it is expected, will lead to a programme of competency assessment and certification. GPS Relevance symbol Because the principal objective of BS 8888 is to provide for accurate, unambiguous technical product specification (TPS), the particular standards provision that constitutes the GPS system of dimensioning and tolerancing will be found throughout the document. Recognizing that on occasion it may be useful to be able to identify and pull together certain GPS elements into a continuous sequence, this edition of BS 8888 introduces the GPS Relevance symbol (see table below) as a means of doing this, for the first time. This segmented symbol is shaded to correlate with the layers of the GPS system itself and is placed in the margin adjacent to the clause or subclause to which it refers. The formation of the symbol is based on the following. An unambiguous GPS is built upon a solid base of foundation standards relating to fundamental principles and presentation media, for example. While the specification of a feature or component defines size, geometry and surface. BSI 2006 iii

6 Where no specific relevance to the GPS system can be identified the symbol is left unshaded. GPS Relevance symbol Symbol Foundation Size Geometry Surface No No No No Yes No No No No Yes No No No No Yes No No No No Yes iv BSI 2006 No Yes Yes No Yes Yes Yes No Presentational conventions The provisions of this standard are presented in roman (i.e. upright) type. Its requirements are expressed in sentences in which the principal auxiliary verb is shall. Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element. All dimensions shown in the figures in this standard are in millimetres. Contractual and legal considerations This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations.

7 1 Scope This British Standard specifies requirements for the preparation of all forms of technical product specification. The requirements cross-refer substantially to International and European Standards which have been implemented as British Standards either in the BS ISO, BS EN, BS EN ISO series or as International Standards re-numbered as British Standards. The requirements are supplemented by commentary and recommendations on technical matters that are considered to be of assistance to users of this standard in the UK and which do not conflict with published International Standards in this field. Annex A and Annex B list cross-referenced standards and other documents, normative and informative respectively, by primary reference. Annex C (normative) sets out requirements for enhanced document security. Annex D (informative) identifies the main differences in approach between the provisions of this standard and those of the American Society of Mechanical Engineers (ASME) Y14.5:1994. Annex E (informative) provides a brief history of the development of BS ISO Annex F (informative) provides a summary report on the concepts that have underwritten the development of technical product specification (TPS) and its primary constituent, geometrical product specification (GPS), to date and discusses some of the drivers for future change. Annex G (informative) gives the rationale behind the development of BS Annex H (informative) gives a list of recommended default choices in response to options that are available in the body of BS NOTE 1 This is the paper-based version of BS 8888, which will henceforth be kept live and updated online. TPS Online, including BS 8888, can be found at accompanied by the full range of cross-referenced standards, all hyperlinked to the relevant reference(s) within the text of the primary standard. When used in paper form, it is necessary that this standard be used in conjunction with the relevant cross-referenced standards NOTE 2 This British Standard is also available in CD-ROM format. 2 References 2.1 Normative references The normative documents listed in Annex A are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. 2.2 Informative references This British Standard refers to other publications that provide information or guidance. These informative documents are listed in Annex B. Care should be taken to ensure that reference is made to the most recent edition. BSI

8 2 BSI Terms and definitions For the purposes of this British Standard, the following terms and definitions apply, together with those given in: BS ISO Technical product documentation Vocabulary Part 1: Terms relating to technical drawings: general and types of drawing BS EN ISO Technical product documentation Vocabulary Part 2: Terms relating to projection methods BS EN ISO Geometrical product specification (GPS) Geometrical features Part 1: General terms and definitions 3.1 date of acceptance point in time at which all interested parties agree that the technical product specification is to be considered finalized to the extent that manufacturing can commence. NOTE 1 This may be identified by other terms, e.g. date of issue. NOTE 2 For the implications of the date of acceptance see geometrical product specification GPS system for defining the shape (geometry), dimensions and surface characteristics of a workpiece 3.3 technical product document TPD means of conveying all or part of a design definition or specification of a product for manufacturing and verification purposes 3.4 technical product specification TPS collection of technical product documents comprising the complete design definition and specification of a product, for manufacturing and verification purposes NOTE 1 NOTE 2 NOTE 3 A TPS was previously called a technical product document set. A TPS can consist of one or more TPDs. A TPS will contain GPS application (see 16.1 for first reference).

9 4 Global standards underpinning BS Introduction The ISO Geometrical Product Specification (GPS) Standards Matrix (see F.4) embodies the concept of global standards that underpin the whole GPS process. This principle is adopted in BS 8888 and the following standards shall be applied as global standards in support of BS BS EN ISO 1 Geometrical Product Specifications (GPS) Standard reference temperature for geometrical product specification and verification BS ISO Technical drawings Dimensioning and tolerancing Non-rigid parts BS EN ISO Geometrical product specifications (GPS) Inspection by measurement of workpieces and measuring equipment Part 1: Decision rules for proving conformance or non-conformance with specifications BS EN ISO Geometrical product specifications (GPS) Inspection by measurement of workpieces and measuring equipment Part 2: Guide to the estimation of uncertainty in GPS measurement, in calibration of measuring equipment and in product verification DD ISO/TS Geometrical product specification (GPS) Part 1: Model for geometrical specification and verification DD ISO/TS Geometrical product specification (GPS) Part 2: Operators and uncertainties PD General metrology Part 1: Basic and general terms (VIM) PD General metrology Part 3: Guide to the expression of uncertainty in measurement (GUM) 4.2 The fundamental TPS principles Introduction The following principles shall always be applied where compliance with BS 8888 is claimed. BSI

10 4 BSI The operator principle A geometrical characteristic is defined by an operator, which is based upon one or more operations and controlled unambiguously by indication in a TPD. COMMENTARY AND RECOMMENDATIONS ON Two types of operators exist: specification operators, which are formulated as virtual measuring procedures, and verification operators, which define the sequence of operations used during the measuring process. (See DD ISO/TS and DD ISO/TS ) The duality principle The duality principle states that the verification operator is the physical implementation of the specification operator. COMMENTARY AND RECOMMENDATIONS ON Were the verification operator (measuring procedure) to be a theoretically perfect implementation, the measurement result would be without measurement uncertainty. The principle that the specification operator defines the requirement in the TPS is the core of the duality principle, which requires that the specification operator be defined independently of any measuring procedure or item of measuring equipment. However, likely deviation of the verification operator from the specification operator indicated in the TPS will contribute to the overall measurement uncertainty (see DD ISO/TS and DD ISO/TS ) The TPS at its acceptance date is definitive, principle. What is not specified in a TPS at the date of acceptance cannot be required. COMMENTARY AND RECOMMENDATIONS ON Requirements only exist where explicitly indicated in the TPS at the date of acceptance or if defined in BS 8888, at that date. The implication of this is that the acceptance date of the TPS implicitly restricts the interpretation of the specification contained within the TPS to those standards in force at the date of acceptance The default principle A complete specification operator can be indicated by the most concise indication for the relevant geometrical characteristic (i.e. the basic GPS). COMMENTARY AND RECOMMENDATIONS ON The basic GPS constitutes the default definition of the specification operator, which might not be visible in the TPS (see DD ISO/TS ) The reference condition principle If not otherwise indicated in the TPS, the reference temperature for the tolerances given in that TPS is 20 C (see BS EN ISO 1) and the workpiece is assumed not to be influenced by any other external physical condition.

11 4.2.7 The uncertainty in conformance principle Where no prior agreement as to the application of uncertainty exists, between two (or more) parties and: where conformance with a specification is to be proven, measurement uncertainty, U reduces the specification to the conformance zone at both tolerance limits and shall always be applied in the interest of the customer purchasing the part; or where non-conformance with a specification is to be proven, measurement uncertainty, U expands the tolerance at both tolerance limits, uncertainty of measurement shall always be applied in the interest of the manufacturer/seller of the part. NOTE It is recognized that a specification will itself contain uncertainty. COMMENTARY AND RECOMMENDATIONS ON Within this TPS system, three categories of uncertainty are defined (DD ISO/TS ): a) specification uncertainty (attributed to the designer); b) correlation uncertainty (attributed to the designer); and c) measurement uncertainty (attributed to the metrologist). 5 Expression of the concept COMMENTARY AND RECOMMENDATIONS Before specifying a technical product, the broad requirement should be established, with particular attention being paid to the functions that the product will be expected to fulfil. The conceptual, design intent can then be depicted in the form of a design layout, scheme or simplified computer-generated model, although this will not normally be used in the detailed TPD for manufacturing purposes. The importance of this stage cannot be over-emphasized. Clear understanding of the purpose and function intended for the eventual product, knowledge of the requirements of the available manufacturing methods and awareness of relevant verification procedures, will help to ensure that the degree of complexity of the specification is appropriate and adequate. It is not the aim of this standard to attempt to instruct or constrain the design process. It is, however, of the greatest importance that the designer presents the product of his design process, i.e. the TPS containing the technical, product specification, in a manner that avoids ambiguity and any risk of misunderstanding or misinterpretation. For this reason, it is imperative that the designer be familiar with the requirements of this standard and aware of the increased precision that its use can bring. For these and many other reasons, management of the overall design process can be complex and the following standards might be found to be of assistance in this field. BS EN BS EN BS Design review Dependability management Part 3-3: Application guide Life cycle costing Design management systems Part 1: Guide to managing innovation BSI

12 BS BS BS Design management systems Part 2: Guide to managing the design of manufactured products Design management systems Part 10: Glossary of terms used in design management Risk management Part 3: Guide to risk analysis of technological systems 6 BSI Types of documentation 6.1 General The careful targeting of TPDs to known or intended users will greatly assist the accuracy with which the specification is converted into the final product. While precision and avoidance of ambiguity should always be paramount, the means employed to convey this information should always be seen to match the capability, or potential capability, of the available or achievable manufacturing facility. Specification beyond this level is unlikely to produce satisfactory results and will often prove expensive, both in terms of the cost of the over-specification itself and in terms of inadequate or unacceptable product. 6.2 Presentation media General The presentation of the drawings shall conform to the following standards. BS EN ISO 5457 BS EN ISO 7200:2004 Technical product documentation Sizes and layout of drawing sheets Technical product documentation Data fields in title blocks and document headers NOTE BS EN ISO 7200:2004 implements ISO 7200:2004 without change. This revision was developed to extend the scope of the standard to include TPS presented wholly or in part in the form of meta-data. Throughout its development, the United Kingdom expressed strong reservation as to the completeness of its content, particularly with regard to the omission of certain elements of the 1984 version still considered to be valid, but was unable to achieve consensus in support of their restoration. For this reason, BS 8888 includes (see 6.2.2) the requirement to apply certain additional standards as part of the application of BS ISO 7200:2004, all of which are already cross-referenced from BS These requirements are not in conflict with the provisions of the revised BS EN ISO 7200:2004 and do no more than restore these missing elements. Particular attention is drawn to Figure 1 and Figure 2 of BS EN ISO 7200:2004, which are provided by way of example but are not wholly correct in that the text is in lower case. These examples should be viewed in conjunction with the relevant clauses of BS EN ISO 3098 (all parts) and BS EN ISO 6428.

13 6.2.2 Application of BS ISO 7200:2004 The application of BS ISO 7200:2004 shall be extended to include relevant provisions of the following standards. BS EN ISO Technical product documentation Lettering Part 0: General requirements BS EN ISO Technical product documentation Lettering Part 2: Latin alphabet, numerals and marks BS EN ISO Technical product documentation Lettering Part 3: Greek alphabet BS EN ISO Technical product documentation Lettering Part 4: Diacritical and particular marks for the Latin alphabet BS EN ISO Technical product documentation Lettering Part 5: CAD lettering of the Latin alphabet, numerals and marks BS EN ISO Technical product documentation Lettering Part 6: Cyrillic alphabet BS EN ISO 6428 Technical drawing requirements for microcopying BS EN ISO 6433 Technical drawings item references BS ISO 7573 Technical drawings Item lists BS ISO Technical Product Documentation Vocabulary Terms relating to technical drawings general and types of drawings Format Drawing sheets and other documents shall be presented in one of the following formats: a) landscape: intended to be viewed with the longest side of the sheet horizontal; b) portrait: intended to be viewed with the longest side of the sheet vertical. NOTE Contrary to BS EN ISO 5457, A4 sheets may be used in landscape or portrait mode Metric reference graduation COMMENTARY AND RECOMMENDATIONS Any metric reference graduation (scale bar) should be figure-less, have a minimum length of 100 mm and be graduated at 10 mm intervals. It should be located symmetrically about a centring mark, near the frame and within the border. It should have a maximum width of 5 mm and the continuous strokes should be of 0.5 mm maximum thickness (see Figure 1). BSI

14 Figure 1 Metric reference graduations 6.3 Combined drawing COMMENTARY AND RECOMMENDATIONS A combined drawing should display an assembly, item list and constituent details, drawn separately but all on the same drawing. 8 BSI Diagram COMMENTARY AND RECOMMENDATIONS The function of a system, or the relationship between component parts, may be depicted in a diagram employing simplified representations, as recommended in the following standards. BS EN ISO Kinematic diagrams Graphical symbols Part 1 BS EN ISO Kinematic diagrams Graphical symbols Part 2 BS EN ISO Kinematic diagrams Graphical symbols Part 3 BS EN ISO Technical drawings Simplified representation for kinematics Part 4: Miscellaneous mechanisms and their components BS Engineering diagram drawing practice Part 1: Recommendations for general principles BS Engineering diagram drawing practice Part 3: Recommendations for mechanical/fluid flow diagrams BS Engineering diagram drawing practice Part 4: Recommendations for logic diagrams BS EN Preparation of documents used in electrotechnology Part 2: Function-oriented diagrams 6.5 Document list Drawing list COMMENTARY AND RECOMMENDATIONS A document list should consist of a list of all graphical representations and selected specifications required to build the assembly from which it derives its title and primary identifier. 7 Scales Scales shall conform to the following standard. BS EN ISO 5455 Technical drawings Scales

15 8 Lines, arrows and terminators 8.1 Lines and terminators Lines shall conform to the following standards, as appropriate. BS EN ISO BS EN ISO BS ISO BS ISO BS ISO BS ISO Lines, terminators and origin indicators Arrows and terminators composed of lines shall conform to the following standard. BS ISO Lettering 9.1 General Technical drawings General principles of presentation Part 20: Basic conventions for lines Technical drawings General principles of presentation Part 21: Preparation of lines by CAD systems Technical drawings General principles of presentation Part 22: Basic conventions and applications for leader lines and reference lines Technical drawings General principles of presentation Part 23: Lines on construction drawings Technical drawings General principles of presentation Part 24: Lines on mechanical engineering drawings Technical drawings General principles of presentation Part 25: Lines on shipbuilding drawings Technical drawings Indications of dimensions and tolerances Part 1: General principles Lettering shall conform to the following standard. BS EN ISO Technical product documentation Lettering Part 0: General requirements Lettering shall also conform to the following standards, as appropriate. BS EN ISO Technical product documentation Lettering Part 2: Latin alphabet, numerals and marks BS EN ISO Technical product documentation Lettering Part 3: Greek alphabet BS EN ISO Technical product documentation Lettering Part 4: Diacritical and particular marks for the Latin alphabet BSI

16 BS EN ISO Technical product documentation Lettering Part 5: CAD lettering of the Latin alphabet, numerals and marks BS EN ISO Technical product documentation Lettering Part 6: Cyrillic alphabet 10 BSI Notes When a landscape-format drawing sheet is used in its normal orientation, with the title block at the bottom right-hand corner, notes shall be lettered parallel to the long side of the sheet. When a landscape-format drawing sheet is used in portrait orientation, the title block shall be located at the left-hand side and notes shall be lettered parallel to the short side of the sheet. COMMENTARY AND RECOMMENDATIONS ON 9.2 Placement Notes of a general nature should, wherever practicable, be grouped together and not distributed over the drawing. Notes relating to specific details should appear near the relevant feature, but not so near as to crowd the view. Underlining Underlining of notes is not recommended. Where emphasis is required, larger characters should be used. 10 Projections Projections shall conform to one of the following standards: BS EN ISO Technical drawings Projection methods Part 2: Orthographic representations BS EN ISO Technical drawings Projection methods Part 3: Axonometric representations BS ISO Technical drawings Projection methods Part 4: Central projection BS EN ISO Technical product documentation Vocabulary Part 2: Terms relating to projection methods NOTE BS EN ISO , Technical drawing Projection methods Part 1: Synopsis, contains a survey of the various projection methods. 11 Views 11.1 General Views shall conform to the following standards. BS ISO BS ISO Technical drawings General principles of presentation Part 30: Basic conventions for views Technical drawings General principles of presentation Part 34: Views on mechanical engineering drawings

17 11.2 Auxiliary views Where true representation of features is necessary, but cannot be achieved on the orthographic views, the features shall be shown in projected auxiliary views. An example is shown in Figure 2. Figure 2 Auxiliary view showing true shape of inclined surface 12 Sections Sections shall conform to the following standards. BS ISO BS ISO BS ISO NOTE ISO and ISO contained presentational defects in some figures (e.g. line types, line thickness, terminators and letter heights), which have, unavoidably, been carried forward to the BS implementations. It is stressed that the text of these standards is technically correct and users should, therefore, regard the figures as illustrations only. 13 Symbols and abbreviations 13.1 General Technical drawings General principles of presentation Part 40: Basic conventions for cuts and sections Technical drawings General principles of presentation Part 44: Sections on mechanical engineering drawings Technical drawings General principles of presentation Part 50: Basic conventions for representing areas on cuts and sections Abbreviations (text equivalents) shall be the same in the singular and plural. Full stops shall not be used except where the abbreviation forms a word (e.g. NO. as an abbreviation for number ) Symbols used for physical quantities and units of measurement shall conform to the following standards, as appropriate. BS ISO 31-0 Specification for quantities, units and symbols Part 0: General principles BS ISO 31-1 Specification for quantities, units and symbols Part 1: Space and time BSI

18 12 BSI 2006 BS ISO 31-2 Specification for quantities, units and symbols Part 2: Periodic and related phenomena BS ISO 31-3 Specification for quantities, units and symbols Part 3: Mechanics BS ISO 31-4 Specification for quantities, units and symbols Part 4: Heat BS ISO 31-5 Specification for quantities, units and symbols Part 5: Electricity and magnetism BS ISO 31-6 Specification for quantities, units and symbols Part 6: Light and related electromagnetic radiations BS ISO 31-7 Specification for quantities, units and symbols Part 7: Acoustics BS ISO 31-8 Specification for quantities, units and symbols Part 8: Physical chemistry and molecular physics BS ISO 31-9 Specification for quantities, units and symbols Part 9: Atomic and nuclear physics BS ISO Specification for quantities, units and symbols Part 10: Nuclear reactions and ionizing radiations BS ISO Specification for quantities, units and symbols Part 11: Mathematical signs and symbols for use in physical sciences and technology BS ISO Specification for quantities, units and symbols Part 12: Characteristic numbers BS ISO Specification for quantities, units and symbols Part 13: Solid state physics BS ISO 1000 Specification for SI Units and recommendation for the use of their multiples and of certain other units 13.2 Standard symbols and abbreviations Symbols appropriate to technical product specification are provided and detailed throughout the suite of documents cross referenced from this standard and these shall be used where appropriate. NOTE 1 It is strongly recommended that abbreviations not be used. Where, in particular technical fields, certain abbreviations are in common use and generally understood, it is accepted that these may continue to be used but new abbreviations shall not be introduced. NOTE 2 Former practice has resulted in certain abbreviations becoming accepted as symbols and these should not be considered to provide precedence for the proliferation of abbreviations COMMENTARY AND RECOMMENDATIONS ON CLAUSE 13 In the existing environment of outsourcing across national borders, every effort is being made to make the use of GPS, independent of language through the adoption of standard symbology. It is for this reason that the continued use of abbreviations is deprecated. Where particular specification requirements cannot be expressed using the available GPS system, full text description should be employed. It is suggested that where such a requirement occurs frequently, this be drawn to the attention of the relevant ISO committee through the appropriate BSI Technical committee.

19 For diagrams used in technical applications, a library of harmonized graphical symbols has been developed with close cooperation between ISO and IEC. This is published in the following series of standards and it is recommended that they be applied wherever practicable to improve the universal applicability of the TPS. BS ISO Graphical symbols for diagrams Part 1: General information and indexes BS ISO Graphical symbols for diagrams Part 2: Symbols having general application BS ISO Graphical symbols for diagrams Part 3: Connections and related devices BS ISO Graphical symbols for diagrams Part 4: Actuators and related devices BS ISO Graphical symbols for diagrams Part 5: Measurement and control devices BS ISO Graphical symbols for diagrams Part 6: Measurement and control functions BS ISO Graphical symbols for diagrams Part 7: Basic mechanical components BS ISO Graphical symbols for diagrams Part 8: Valves and dampers BS ISO Graphical symbols for diagrams Part 9: Pumps, compressors and fans BS ISO Graphical symbols for diagrams Part 10: Fluid power converters BS ISO Graphical symbols for diagrams Part 11: Devices for heat transfer and heat engines BS ISO Graphical symbols for diagrams Part 12: Devices for separating, purification and mixing 14 Representation of features Conventions used for the representation of features shall conform to the following standards, as appropriate. BS EN ISO 4063 Welding and allied processes Nomenclature of processes and reference numbers BS EN ISO 5261 Technical drawings Simplified representation of bars and profile sections BS EN ISO Technical drawings Simplified representation of the assembly of parts with fasteners Part 1: General principles BS EN ISO Technical drawings Screw threads and threaded parts Part 1: General conventions BS EN ISO Technical drawings Screw threads and threaded parts Part 2: Screw thread inserts BS EN ISO Technical drawings Screw threads and threaded parts Part 3: Simplified representation BS EN ISO 6411 Technical drawings Simplified representation of centre holes BSI

20 BS EN ISO 6413 Technical drawings Representation of splines and serrations BS ISO Technical drawings Edges of unidentified shape Vocabulary and indications BS EN ISO 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 BS EN ISO Technical drawings Symbolic presentation and indication of adhesive, fold and pressed joints BS EN Welded, brazed and soldered joints Symbolic representation on drawings NOTE The BS ISO 128 series of standards covers the general subject of feature representation. 14 BSI Representation of components 15.1 General Conventions used for the representation of components shall conform to the following standards, as appropriate. BS EN ISO Technical product documentation Springs Part 1: Simplified representation BS EN ISO Technical product documentation Springs Part 2: Presentation of data for cylindrical helical compression springs BS EN ISO Technical product documentation Springs Part 3: Vocabulary BS EN ISO 2203 Technical drawings Conventional representation of gears BS Graphic symbols and circuit diagrams for fluid power systems and components Part 1: Specification for graphic symbols BS Graphical symbols for components of servomechanisms Part 1: Transductors and magnetic amplifiers BS Graphical symbols for components of servo-mechanisms Part 2: General servo-mechanisms BS EN ISO Technical drawings Simplified representation of the assembly of parts with fasteners Part 1: General principles BS EN ISO Technical drawings Screw threads and threaded parts Part 1: General conventions BS EN ISO Technical drawings Screw threads and threaded parts Part 2: Screw thread inserts BS EN ISO Technical drawings Screw threads and threaded parts Part 3: Simplified representation

21 BS EN ISO Technical drawings Simplified representation of pipelines General rules and orthogonal representation BS EN ISO Technical drawings Simplified representation of pipelines Isometric projection BS EN ISO Technical drawings Simplified representation of pipelines Terminal features of ventilation and drainage systems BS EN ISO Technical drawings Roller bearings Part 1: General simplified representation BS EN ISO Technical drawings Roller bearings Part 2: Detailed simplified representation BS EN ISO Technical drawings Seals for dynamic application Part 1: General simplified representation BS EN ISO Technical drawings Seals for dynamic application Part 2: Detailed simplified representation NOTE The BS ISO 128 series of standards covers the general subject of component representation Representation of moulded, cast and forged components Dimensional tolerancing for metal and metal alloy castings shall conform to BS 6615:1996. COMMENTARY AND RECOMMENDATIONS ON 15.2 It is recommended that tolerances for the dimensions of plastics mouldings be applied in accordance with the system provided in BS ISO 8062:1994 which is implemented in full by BS 6615 is currently undergoing extensive revision under the generic title Geometrical product specifications (GPS) Dimensional and geometrical tolerances for moulded parts. This will be published in three parts: Part 1: Vocabulary; Part 2: Rules; and Part 3: General dimensional and geometrical tolerances and machining allowances for castings. Parts 1 and 3 of ISO 8062 will be published as BS ISO 8062 Part 1 and Part 3, early in 2007 and it is expected that Part 2 will become available by the end of that year. Together, the three parts of BS ISO 8062:2007 will cancel and replace ISO 8062:1994 of which they will constitute a technical revision. Future action with regard to BS 7010 will be decided at that time. BSI

22 16 BSI Dimensioning and tolerancing 16.1 Interpretations of limits of size for the control of form General COMMENTARY AND RECOMMENDATIONS The limits of size of an individual feature-of-size may be defined using one of the following principles: a) the principle of independency of size and form, where the limits of size are intended to exercise control only over the size of the feature-of-size, and not to exercise any control over its form; or b) the principle of dependency of size and form, where the limits of size are intended to exercise control over the form of the feature-of-size as well as its size. In both cases, an individual feature-of-size is defined as one cylindrical or spherical surface or as a pair of parallel surfaces, each feature-of-size being defined by a linear dimension. In neither case do the limits of size control the orientation of, or the spatial relationship between, individual features-of-size. If such relationships are functionally important, they need to be controlled separately by specifying geometrical tolerances. For example, a cube consists of three individual features-of-size, each composed of a pair of plane parallel surfaces. The perpendicularity of those individual features-of-size is not controlled by their size tolerances, and therefore if the function requires a perpendicularity tolerance, it should be specified. If the principle of dependency is applied then BS ISO 8015 becomes an informative document only Limits of size with independency of size and form COMMENTARY AND RECOMMENDATIONS With independency of size and form, limits of size control only the actual local sizes (two-point measurements) of a feature-of-size, and not its deviations of form (e.g. the circularity and straightness deviations of a cylindrical feature, or the flatness deviations of two parallel plane surfaces). Therefore, at the maximum material limit of size, the maximum limiting value of the form tolerance still applies (i.e. at maximum material limit of size it is permissible to have imperfect form). When applying the principle of independency it is necessary to specify each and every form tolerance (see Figure 3). According to the principle of independency, each specified dimensional and geometrical requirement on a drawing is met independently, unless a particular relationship is specified. Consequently, if a particular relationship of size and form is required, it needs to be specified on the drawing. This can be achieved by the use of the envelope requirement (see BS ISO 8015) or material modifiers. In effect this introduces the boundary or envelope of perfect form in the same manner as the principle of dependency (i.e. the maximum material limit of size defines the boundary or envelope of perfect form for the relevant surfaces).

23 According to the principle of independency, each specified dimensional and geometrical requirement on a drawing is met independently, unless a particular relationship is specified. Therefore, where no relationship is specified, the geometrical tolerance applies regardless of feature size, and the two requirements are treated as unrelated (see Figure 3). Consequently, if a particular relationship of: size and form; or size and location; or size and orientation; is required, it needs to be specified on the drawing. Figure 3 Interpretations using the principle of independency for a cylindrical component for which a tolerance of size only is given on the drawing 25,0 24,9 a) Drawing presentation NOTE There is no straightness control. Measurements a, b and c will lie between 25.0 mm and 24.9 mm, meeting the drawing requirement using two-point measurement only. The form is not controlled. b) Permissible interpretation: straightness 25,0 a b NOTE For any cross-section of the cylinder, there is no roundness control. c) Permissible interpretation: roundness c Maximum size Maximum roundness deviation (resulting from a lobed form) BSI

24 18 BSI Limits of size with mutual dependency of size and form COMMENTARY AND RECOMMENDATIONS Where the feature-of-size is defined by limits of size only, the maximum material limit of size (i.e. the high limit of size of an external feature or the low limit of size of an internal feature) defines the boundary or envelope of perfect form for the relevant surfaces. If an individual feature-of-size is everywhere on its maximum material limit of size, the feature will have perfect form. If the individual feature-of-size is not on its maximum material size, errors in form will be acceptable provided that no part of the finished surfaces extends beyond the maximum material boundary or envelope of the perfect form, and that the feature-of-size is everywhere in accordance with its specified limits of size (see Figure 4). NOTE An external feature is also known as a shaft type feature and an internal feature is also known as a hole type feature. If the limits of size for the feature-of-size is at the least material limit of size (i.e. the low limit of size of an external feature or the high limit of size of an internal feature) then the form deviation can be at its maximum within the confines of the boundary or envelope of perfect form. If the limits of size specified permit form deviations large enough to be functionally unacceptable as the feature-of-size approaches its least material limit size, then these deviations can be controlled by specifying appropriate form tolerances. Such form tolerances will be maximum limiting values. The effect of these values will decrease as the feature-of-size approaches its maximum material limit of size, as no part of the finished surfaces of the feature-of-size is permitted to extend beyond the maximum material limit of perfect form. Where the principle of dependency is applied, verification of the feature-of-size and permissible form deviation is possible using go/no-go gauging techniques. The Taylor principle states that effective verification can only take place with a gauge touching the whole feature, ensuring that a mating part will go at the maximum material limit, while rejection checking is accomplished as a single examination with the two-point method (verification of least material limits). The application of the dependency principle however, implies that all features of size will have perfect form at maximum material limits and could impose higher production costs.

25 Figure 4 Interpretation of limits of size with dependency of size and form ,1 20-0,1 a) Drawing specification General 19,9 19, ,9 Dimensioning and tolerancing shall conform to the following standards, as appropriate: 20,1 b) Possible extreme errors of form BS ISO Technical drawings Indications of dimensions and tolerances Part 1: General principles BS ISO 406 Technical drawings Tolerancing of linear and angular dimensions BS EN ISO 1119 Geometrical product specifications (GPS) Series of conical tapers and taper angles 20,1 20,1 20 BSI

26 20 BSI 2006 BS EN ISO 1660 Technical drawings Dimensioning and tolerancing of profiles BS Limits and fits for engineering Part 1: Limits and tolerances BS Limits and fits for engineering Part 2: Guide to the selection of fits in BS 1916:Part 1 BS Limits and fits for engineering Part 3: Recommendations for tolerances, limits and fits for large diameters BS ISO 3040 Technical drawings Dimensioning and tolerancing Cones BS ISO limits and fits Specification for system of cone (taper) fits for cones from C = 1:3 to 1:500, lengths from 6 mm to 630 mm and diameters up to 500 mm BS ISO limits and fits Specification for system of cone tolerances for conical workpieces from C = 1:3 to 1:500 and lengths from 6 mm to 630 mm BS EN ISO 5458 Geometrical Product Specifications (GPS) Geometrical tolerancing Positional tolerancing BS EN ISO Technical drawings Screw threads and threaded parts Part 1: General conventions BS 6615 Specification for dimensional tolerances for metal and metal alloy castings BS 7010 Code of practice for a system of tolerances for the dimensions of plastic mouldings BS EN ISO 7083 Technical drawings Symbols for geometrical tolerancing Proportions and dimensions BS ISO 8015 Technical drawings Fundamental tolerancing principle BS ISO Technical drawings Dimensioning and tolerancing Non-rigid parts BS ISO Welding General tolerances for welded constructions Dimensions for lengths and angles Shape and position BS EN ISO system of limits and fits Part 1: Bases of tolerances, deviations and fits BS EN ISO system of limits and fits Part 2: Tables of standard tolerance grades and limit deviations for holes and shafts COMMENTARY AND RECOMMENDATIONS ON 16.2 Gaps between extension lines and features. It is the practice in the UK to leave a small gap between the extension line and the feature. In BS ISO the illustrated examples do not show a gap but 5.3, includes the text, in certain technical fields, a gap between the feature and the beginning of the extension line is acceptable. The UK has always held to the view that for reasons of clarity a gap is preferable and given that in the revised standard the gap is permissible, it is intended that the current UK practice should be maintained.

27 16.3 Presentation of decimals Decimal marker The decimal marker shall be a comma Non-indicated decimals in tolerances Non-indicated decimals in a tolerance indication shall be taken as zeros e.g. 0,2 is the same as 0, COMMENTARY AND RECOMMENDATIONS ON 16.3 It is recommended that each group of three digits, counting from the decimal marker to the left and to the right, be separated from other digits by a small space (e.g ,067 8). In view of the requirement of , the use of a comma or a point for this purpose is deprecated, i.e. it is further recommended that separation of items in lists be effected by the use of a semi-colon. (See BS ISO 31-0, Specification for quantities, units and symbols Part 0: General principles.) 16.4 Keyways Figure 5 Keyways in hubs or shafts shall be dimensioned by one of the methods shown in Figure 5. NOTE Further 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 Part 2: Woodruff keys and keyways. Dimensioning of keyways a) Parallel hub b) Tapered keyway in parallel hub d) Parallel shaft e) Parallel keyway in tapered shaft f) Parallel shaft g) Tapered shaft c) Parallel keyway in tapered hub BSI

28 16.5 Screw threads Screw threads shall be specified according to functional requirement. COMMENTARY AND RECOMMENDATIONS ON 16.5 The following standards provide the definition for metric ISO screw threads. BS ISO 261 ISO general purpose metric screw threads General plan. BS ISO 262 ISO general purpose metric screw threads Selected sizes for screws, bolts and nuts. BS ISO ISO general purpose metric screw threads Tolerances Part 1: Principles and basic data 16.6 Methods of specifying tolerances Figure 6 22 BSI 2006 COMMENTARY AND RECOMMENDATIONS The necessary tolerances can be specified in one or more of the following ways: a) separate indication on the drawing; b) reference to general tolerances noted on the drawing; c) reference to a standard containing general tolerances; d) reference to other documents General tolerancing Examples of general tolerance notes TOLERANCE EXCEPT WHERE OTHERWISE STATED + X - TOLERANCE ON CAST THICKNESS + - X % COMMENTARY AND RECOMMENDATIONS If reference to BS EN or BS EN for general tolerances is inappropriate, general tolerance notes may be used to apply a common tolerance to many of the features on a drawing. The example shown in Figure 6 illustrates the wide field of application of this system. Due to the inherent risk of unintentionally over-specifying form and orientation controls that can result from the use of general geometrical tolerances, reference to BS EN is inadvisable. TOLERANCES EXCEPT WHERE OTHERWISE STATED SIZE TOLERANCE - UP TO X + - A OVER X UP TO XX + - B OVER XX UP TO XXX + - C OVER XXX D ON ANGLES + - E FOR TOLERANCES ON FORGING DIMENSIONS SEE BS EN

29 17 Geometrical tolerancing 17.1 General Geometrical tolerancing shall conform to the following standards, as appropriate. BS ISO 1101 Technical drawings Geometrical tolerancing Tolerancing of form, orientation, location and run-out Generalities, definitions, symbols, indications on drawings BS ISO 2692 Technical drawings Geometrical tolerancing Maximum material principle BS EN ISO 5458 Geometrical Product Specifications (GPS) Geometrical tolerancing Positional tolerancing BS ISO 5459 Technical drawings Geometrical tolerancing Datums and datum-systems for geometrical tolerances BS EN ISO 7083 Technical drawings Symbols for geometrical tolerancing Proportions and dimensions BS ISO Technical drawings Tolerancing of orientation and location Projected tolerance zone 18 Surface texture indication Indication of surface texture shall conform to the following standards. BS EN ISO 1302 Geometrical Product Specifications (GPS) Indication of surface texture in technical product documentation BS EN ISO 8785 Geometrical product specification (GPS) Surface imperfections Terms definitions and parameters The correct application of BS EN ISO 1302 requires the use of the following standards. Other normative references of BS EN ISO 1302 are also referenced in this standard. BS EN ISO 3274 Geometrical Product Specifications (GPS) Surface texture: profile method Nominal characteristics of contact (stylus) instruments BS EN ISO 4287 Geometrical Product Specifications (GPS) Surface texture: Profile method Terms, definitions and surface texture parameters BS EN ISO 4288 Geometrical Product Specification (GPS) Surface texture Profile method: Rules and procedures for the assessment of surface texture BS ISO Technical drawings Simplified representation of moulded, cast and forged parts BSI

30 24 BSI 2006 BS EN ISO Geometrical Product Specifications (GPS) Surface texture: Profile method Metrological characteristics of phase correct filters BS EN ISO Geometrical Product Specifications (GPS) Surface texture: Profile method Motif parameters BS EN ISO Geometric Product Specifications (GPS) Surface texture: Profile method Surfaces having stratified functional properties Part 1: Filtering and general measurement conditions BS EN ISO Geometrical Product Specifications (GPS) Surface texture: Profile method Surfaces having stratified functional properties Part 2: Height characterization using the linear material ration curve BS EN ISO Geometrical Product Specifications (GPS) Surface texture: Profile method Surfaces having stratified functional properties Part 3: Height characterization using the material probability curve BS EN ISO Geometrical Product Specifications (GPS) Inspection by measurement of workpieces and measuring equipment Part 1: Decision rules for proving conformance or non-conformance with specifications BS EN ISO Geometrical Product Specifications (GPS) Geometrical features Part 1: General terms and definitions BS EN ISO Design of graphical symbols for use in the technical documentation of products Part 1: Basic rules NOTE Although it is not usual practice to make secondary references such as these, BS EN ISO 1302 itself is of such significance that it is considered appropriate to ensure their inclusion in the BS 8888 kits in this way. 19 Graphical representation and annotation of 3D data (3D modelling output) Graphical representation and annotation of 3D models shall conform to the following standards. DD Technical product documentation Digital product definition Data practices COMMENTARY AND RECOMMENDATIONS ON CLAUSE 19 At time of publication of this standard, BS ISO is undergoing the final stages of approval. DD contains the draft of ISO circulated for comment, which is not expected to change substantially at final publication.

31 20 Security 20.1 Introduction Many TPSs have minimal requirements for security, other than that provided by general handling and storage procedures (see Clause 21). However, where specific need for a general level of security is identified, the following requirements shall be met General security Procedures for ensuring the security of TPDs and TPSs shall conform to the following standard. BS EN ISO Technical product documentation Handling of computer-based technical information Part 1: Security requirements 20.3 Enhanced security Where enhanced security is claimed, the requirements of Annex C to this standard shall be met, in addition to those in Security level identification The level of security attributed to any given TPS shall be clearly identified by the relevant marking placed adjacent to the title or title block, of every TPD making up that TPS. 21 Storage and retrieval Methods for storage and retrieval of the document shall conform to the following standards, as appropriate. BS EN ISO 6428 Technical drawings Requirements for microcopying BS EN ISO Technical product documentation Handling of computer-based technical information Part 2: Original documentation BS EN ISO Technical product documentation Handling of computer-based technical information Part 3: Phases in the product design process BS EN ISO Technical product documentation Handling of computer-based technical information Part 4: Document management and retrieval systems BS ISO Technical product documentation Handling of computer-based technical information Part 5: Documentation in the conceptual design stage of the development phase BSI

32 26 BSI Marking NOTE The marking of a TPD or TPS with the number of this standard constitutes a claim that the appropriate requirements of all relevant cross-referenced standards, in addition to the requirements directly stated in BS 8888, have been met. Attention is drawn to the TPS at its acceptance date is definitive, principle (4.2.4) BS 8888 Technical product documents prepared in accordance with the requirements of this standard shall be marked with the number of this standard, i.e. BS 8888, in a prominent location BS 8888 (enhanced security) Technical product documents prepared in accordance with the requirements of this standard and meeting the requirements for enhanced security specified in Annex C, shall be marked with the number of this standard followed by a suffix /D, i.e. BS 8888/D, in a prominent location Tolerancing system Figure 7 Figure 8 Where the TPD or TPS has been prepared using the independency system of tolerancing (see commentary and recommendations on Clause 16), the mark identifying the number of this standard shall be supplemented by the letter I contained within an equilateral triangle, as shown in Figure 7. Method of indicating that the independency system of tolerancing has been used BS 8888 Where the TPD or TPS has been prepared using the dependency system of tolerancing (see commentary and recommendations on Clause 16), the mark identifying the number of this standard shall be supplemented by the letter D contained within an equilateral triangle, as shown in Figure 8. Method of indicating that the dependency system of tolerancing has been used BS 8888 I D

33 23 Protection notices COMMENTARY AND RECOMMENDATIONS It is suggested that where it is considered appropriate to place restrictions on the use of technical product documentation, the recommendations contained in the following standard be applied. BS ISO Technical product documentation Protection notices for restricting the use of documents and products BSI

34 28 BSI 2006 Annex A (normative) Normative references NOTE The figures in this annex are reproduced from other standards and are for purely illustrative purposes. In some figures, details and clarity have been lost in the reproduction and reduction process. Table A.1 lists standards containing requirements which need to be met in order to claim compliance with BS Where available, the table also gives a typical example of an illustration from each standard. Abbreviations used in the table GPP: General principles of presentation GPS: Geometrical product specifications GT: Geometrical tolerancing HCTI: Handling of computer-based technical information SQUS: Specification for quantities, units and symbols STTP: Screw threads and threaded parts TD: Technical drawings TPD: Technical product documentation BS 8888:2006 Table A.1 Normative references BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 4.1, 4.2 BS EN ISO 1 Standard reference temperature for geometrical product specification Not available and verification , BS ISO 31-0 Quantities and units Not available BS ISO 31-1 SQUS Part 1: Space and time Not available BS ISO 31-2 SQUS Part 2: Periodic and related phenomena Not available BS ISO 31-3 SQUS Part 3: Mechanics Not available BS ISO 31-4 SQUS Part 4: Heat Not available BS ISO 31-5 SQUS Part 5: Electricity and magnetism Not available BS ISO 31-6 SQUS Part 6: Light and related electromagnetic radiations Not available

35 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration BS ISO 31-7 SQUS Part 7: Acoustics Not available BS ISO 31-8 SQUS Part 8: Physical chemistry and molecular Not available physics BS ISO 31-9 SQUS Part 9: Atomic and nuclear physics Not available BS ISO SQUS Part 10: Nuclear reactions and ionizing Not available radiations BS ISO SQUS Part 11: Mathematical signs and symbols for use Not available in physical sciences and technology BS ISO SQUS Part 12: Characteristic numbers Not available BS ISO SQUS Part 13: Solid state physics Not available 8.1 BS EN ISO TD GPP Part 20: Basic conventions for lines continuous line 8.1 BS EN ISO TD GPP Part 21: Preparation of lines by CAD systems Not available 8.1 BS ISO TD GPP Part 22: Basic conventions and applications for leader lines and reference lines dashed line dashed spaced line BSI BS ISO TD GPP Part 23: Lines on construction drawings Dashed narrow line existing contours on landscape drawings subdivision of plant beds/grass hidden outlines BS 8888:2006

36 30 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 8.1 BS ISO TD GPP Part 24: Lines on mechanical engineering drawings Long-dashed dotted wide line indication of (limited) required areas of surface treatment, e.g. heat treatment position of cutting planes BS 8888: BS ISO TD GPP Part 25: Lines on shipbuilding drawings Dashed narrow line hidden edges 11.1 BS ISO TD GPP Part 30: Basic conventions for views hidden profiles

37 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 11.1 BS ISO TD GPP Part 34: Views on mechanical engineering drawings 12 BS ISO TD GPP Part 40: Basic conventions for cuts and sections 12 BS ISO TD GPP Part 44: Sections on mechanical engineering drawings BS 8888:2006 BSI

38 32 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 12 BS ISO TD GPP Part 50: Basic conventions for representing areas on cuts and sections BS 8888: , 16.2 BS ISO TD Indications of dimensions and tolerances Part 1: General principles. Arrowhead, closed and filled 30 Arrowhead, open 30 NOTE Annex H gives preferred options for dimensioning, tolerancing and lettering.

39 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 16.2 BS ISO 406 TD Tolerancing of linear and angular dimensions 30 f7 30 f7-0,020-0, f7 29,980 29, BS ISO 1000 Specification for SI Units and recommendations for the use of their multiples and of certain other units 17.1 BS ISO 1101 TD GT Tolerancing of form, orientation, location and run-out Generalities, definitions, symbols, indications on drawings 16.2 BS EN ISO 1119 GPS Series of conical tapers and taper angles Form Orientation Location Run-out Modifier symbols Not available u c e g k d f b a k d j r i k d h t C Z LD MD PD LE NC AC S α /2 d D α L 18 BS EN ISO 1302 GPS Indication of surface texture in technical product documentation BS 8888:2006 BSI

40 34 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 16.2 BS EN ISO 1660 TD Dimensioning and tolerancing of profiles BS 8888: BS Limits and fits for engineering Part 1: Limits and tolerances 16.2 BS Limits and fits for engineering Part 2: Guide to the selection of fits in BS 1916:Part 1 Not available 16.2 BS Limits and fits for engineering Part 3: Recommendations for tolerances, limits and fits for large diameters Not available 15.1 BS EN ISO TPD Springs Part 1: Simplified representation View Section Simplified

41 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 15.1 BS EN ISO TPD Springs Part 2: Presentation of data for cylindrical, helical, compression springs 15.1 BS EN ISO TPD Springs Part 3: Vocabulary Not available 15.1 BS EN ISO 2203 TD Conventional representation of gears BSI BS ISO 2692 TD GT Maximum material principle m maximum material requirement l least material requirement BS 8888:2006

42 36 BSI 2006 Table A.1 Normative references (continued) BS 8888 Standard referenced Title of the standard Typical illustration (sub)clause 15.1 BS Graphic symbols and circuit diagrams for fluid power systems and components Part 1: Specification for graphic symbols Not available 16.2 BS ISO 3040 TD Dimensioning and tolerancing Cones BS 8888: , 6.2.2, , 6.2.2, 9.1 BS EN ISO TPD Lettering Part 0: General requirements Not available BS EN ISO TPD Lettering Part 2: Latin alphabet, numerals and marks 6.2.1, 6.2.2, 9.1 BS EN ISO TPD Lettering Part 3: Greek alphabet NOTE BS 8888 non-preferred. Annex H gives preferred options for dimensioning, tolerancing and lettering , 6.2.2, 9.1 BS EN ISO TPD Lettering Part 4: Diacritical and particular marks for the Latin alphabet

43 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 6.2.1, 6.2.2, 9.1 BS EN ISO TPD Lettering Part 5: CAD lettering of the Latin alphabet, numerals and marks 6.2.1, 6.2.2, 9.1 BS EN ISO TPD Lettering Part 6: Cyrillic alphabet 15.1 BS Graphical symbols for components of servo-mechanisms Part 1: Transductors and magnetic amplifiers 15.1 BS Graphical symbols for components of servo-mechanisms Part 2: General servo-mechanisms BSI BS EN ISO 3274 GPS Surface texture: Profile method Nominal characteristics of contact (stylus) instruments 14 BS EN ISO 4063 Welding and allied processes Nomenclature of processes and reference numbers 18 BS EN ISO 4287 GPS Surface texture: Profile method Terms, definitions and surface texture parameters Not available Not available Not available BS 8888:2006

44 38 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 18 BS EN ISO 4288 GPS Surface texture: profile method Rules and procedures for the assessment of surface texture 16.2 BS ISO limits and fits Specification for system of cone (taper) fits for cones from C = 1:3 to 1:500, lengths from 6 mm to 630 mm and diameters up to 500 mm 16.2 BS ISO limits and fits Specification for system of cone tolerances for cones from C = 1:3 to 1:500, lengths from 6 mm to 630 mm 6.4 BS Engineering diagram drawing practice Part 1: Recommendations for general principles 6.4 BS Engineering diagram drawing practice Part 3: Recommendations for mechanical/ fluid flow diagrams 6.4 BS Engineering diagram drawing practice Part 4: Recommendations for logic diagrams 14 BS EN ISO 5261 TD Simplified representation of bars and profile sections Angle section Not available Not available Not available Not available Not available Not available Alternate symbol: L BS 8888: BS EN ISO 5455 TD Scales Not available 10 BS EN ISO TD Projection methods Part 2: Orthographic representations

45 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 10 BS EN ISO TD Projection methods Part 3: Axonometric representations 10 BS ISO TD Projection methods Part 4: Central projection BS 8888:2006 BSI

46 40 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 6.2.1, BS EN ISO 5457 TPD Sizes and layout of drawing sheets BS 8888: , 17.1 BS EN ISO 5458 GPS GT Positional tolerancing 17.1 BS ISO 5459 TD GT Datums and datum-systems for geometrical tolerances A A NOTE Annex H gives preferred options for dimensioning, tolerancing and lettering.

47 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 14, 15 BS EN ISO TD Simplified representation of the assembly of parts with fasteners Part 1: General principles 14, 15, 16.2 BS EN ISO TD STTP Part 1: General conventions 14, 15 BS EN ISO TD STTP Part 2: Screw thread inserts Detailed Conventional Simplified Insert 14, 15 BS EN ISO TD STTP Part 3: Simplified representation Hexagon head screw BSI BS EN ISO 6411 TD Simplified representation of centre holes BS 8888:2006

48 42 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 15 BS EN ISO TD Simplified representation of pipelines Part 1: General rules and orthogonal representation BS 8888: BS EN ISO TD Simplified representation of pipelines Part 2: Isometric projection

49 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 15 BS EN ISO TD Simplified representation of pipelines Part 3: Terminal features of ventilation and drainage systems Scupper 14 BS EN ISO 6413 TD Representations of splines and serrations 6.2.1, 6.2.2, BS EN ISO 6428 TD Requirements for microcopying Not available BS EN ISO 6433 TD Item references BSI PD General metrology Part 1: Basic and general terms (VIM) 4.1 PD General metrology Part 3: Guide to the expression of uncertainty in measurement (GUM) Not available Not available BS 8888:2006

50 44 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 15.2, 16.2 BS 6615 Specification for dimensional tolerances for metal and metal alloy castings 16.2, 17.1 BS EN ISO 7083 TD Symbols for geometrical tolerancing Proportions and dimensions Not available BS 8888: , BS EN ISO 7200:2004 TPD Data fields in title blocks and document headers Not available BS ISO 7573 TD Item lists Not available , , 16.2 BS ISO 8015 TD Fundamental tolerancing principle 18 BS EN ISO 8785 GPS Surface imperfections Terms, definitions and parameters E 15.1 BS EN ISO TD Rolling bearings Part 1: General simplified representation 15.1 BS EN ISO TD Rolling bearings Part 2: Detailed simplified representation

51 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 15.1 BS EN ISO TD Seals for dynamic application Part 1: General simplified representation 15.1 BS EN ISO TD Seals for dynamic application Part 2: Detailed simplified representation 18 BS ISO TD Simplified representation of moulded, cast and forged parts BSI , BS ISO TPD Vocabulary Part 1: Terms relating to technical drawings: general and types of drawing 3, 10 BS EN ISO TPD Vocabulary Part 2: Terms relating to projection methods Not available Not available BS 8888:2006

52 46 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 17.1 BS ISO TD Tolerancing of orientation and location Projected tolerance zone BS 8888: , 16.2 BS ISO TD Dimensioning and tolerancing Non-rigid parts 20.2 BS EN ISO TPD HCTI Part 1: Security requirements Not available 21 BS EN ISO TPD HCTI Part 2: Original documentation Not available

53 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 21 BS EN ISO TPD HCTI Part 3: Phases in the product design process 21 BS EN ISO TPD HCTI Part 4: Document management and retrieval systems 21 BS ISO TPD HCTI Part 5: Documentation in the conceptual design stage of the development phase 18 BS EN ISO GPS Surface texture: Profile method Metrological characteristics of phase correct filters 18 BS EN ISO GPS Surface texture: Profile method Motif parameters 18 BS EN ISO GPS Surface texture: Profile method Surfaces having stratified functional properties Part 1: Filtering and general measurement conditions 18 BS EN ISO GPS Surface texture: Profile method Part 2: Height characterization using the linear material ration curve 18 BS EN ISO GPS Surface texture: Profile method Part 3: Height characterization using the material probability curve 14 BS ISO TD Edges of undefined shape Vocabulary and indications 16.2 BS EN ISO Welding General tolerances for welded constructions Dimensions for length and angles Shape and position Not available Not available Not available Not available Not available Not available Not available Not available Not available Not available BS 8888:2006 BSI

54 48 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 4.1, 18 BS EN ISO GPS Inspection by measurement of workpieces and measuring equipment Part 1: Decision rules for proving conformance or non-conformance with specifications BS 8888: DD ENV ISO GPS Inspection by measurement of workpieces and measuring equipment Part 2: Guide to the estimation of uncertainty in GPS measurement, in calibration of measuring equipment and in product verification 3, 18 BS EN ISO GPS Geometrical features Part 1: General terms and definitions Not available Drawing Workpiece Extraction Association 14 BS EN ISO GPS Geometrical features Part 2: Extracted median line of a cylinder and a cone, extracted median surface, local size of an extracted feature Not available

55 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 14 BS EN ISO TD Symbolic presentation and indication of adhesive, fold and pressed joints Fold t x w 19 DD TPD Digital product definition Data practices Not available 4.1, 4.2 DD ISO/TS GPS Part 1: Model for geometrical specification and Not available verification 4.1, 4.2 DD ISO/TS GPS Part 2: Operators and uncertainties Not available 16.2, D.5 BS EN ISO system of limits and fits Part 1: Bases of tolerances, deviations and fits 16.2 BS EN ISO system of limits and fits Part 2: Tables of standard tolerance grades and limit deviations for holes and shafts BS 8888:2006 BSI

56 50 BSI 2006 Table A.1 Normative references (continued) BS 8888 (sub)clause Standard referenced Title of the standard Typical illustration 14 BS EN Welded, brazed and soldered joints Symbolic representation on drawings BS 8888: BS EN General tolerances Part 1: Tolerances for linear and angular dimensions without individual tolerance indications 16.7 BS EN General tolerances Part 2: Tolerances for features without individual tolerance indications 18 BS EN ISO Design of graphical symbols for use in the technical documentation of products Part 1: Basic rules NOTE Annex H gives preferred options for dimensioning, tolerancing and lettering Not available Not available Not available

57 Annex B (informative) Table B.1 Informative references Table B.1 lists standards and other documents which provide information or guidance relevant to the application of BS NOTE Standards which are referred to both normatively and informatively are listed in Annex A only. Abbreviations used in the table GSD: Graphical symbols for diagrams SMKK: Specification for metric keys and keyways TD: Technical drawings DMS: Design management systems Informative references BS 8888 (sub)clause Referenced document Title of document 6.4 BS EN ISO Kinematic diagrams Graphical symbols Part BS EN ISO Kinematic diagrams Graphical symbols Part BS EN ISO Kinematic diagrams Graphical symbols Part BS EN ISO TD Simplified representation for kinematics Part 4: Miscellaneous mechanisms and their components 16.4 BS SMKK Part 1: Parallel and taper keys 16.4 BS SMKK Part 2: Woodruff keys and keyways 10 BS EN ISO TD Projection methods Part 1: Synopsis 5 BS EN Design review 5 BS EN Dependability management Part 3-3: Application guide Life cycle costing 5 BS DMS Part 1: Guide to managing innovation 5 BS DMS Part 2: Guide to managing the design of manufactured products 5 BS DMS Part 10: Glossary of terms used in design management 5 BS Risk management Part 3: Guide to Risk analysis of technological systems 16.7 BS EN Steel die forgings Tolerances on dimensions Part 1: Drop and vertical press forgings 13 BS ISO GSD Part 1: General information and indexes 13 BS ISO GSD Part 2: Symbols having general application BSI

58 Table B.1 Informative references (continued) Annex C (normative) 52 BSI 2006 BS 8888 (sub)clause Document security Enhanced C.1 Introduction Referenced document Title of document 13 BS ISO GSD Part 3: Connections and related devices 13 BS ISO GSD Part 4: Actuators and related devices 13 BS ISO GSD Part 5: Measurement and control devices 13 BS ISO GSD Part 6: Measurement and control functions 13 BS ISO GSD Part 7: Basic mechanical components 13 BS ISO GSD Part 8: Valves and dampers 13 BS ISO GSD Part 9: Pumps, compressors and fans 13 BS ISO GSD Part 10: Fluid power converters 13 BS ISO GSD Part 11: Devices for heat transfer and heat engines 13 BS ISO GSD Part 12: Devices for separating, purification and mixing 23 BS ISO TPD Protection notices for restricting the use of documents and products 6.4 BS EN Preparation of documents used in electrotechnology Part 2: Function-oriented diagrams Where requirements for enhanced security are known to exist, the procedures identified in this annex shall be applied in addition to those specified in Clause 20. C.2 Identification of security classification C.2.1 Any required security classification and/or caveat, shall be inserted in the TPS, immediately after classified information is incorporated. C.2.2 Each sheet shall be classified according to its content. C.2.3 The security classification shall always appear at the top and bottom of A4 sheets and at the top left and bottom right hand corners of sheets larger than A4. C.2.4 The security classification shall either be: a) larger than the largest text used in the TPS; or b) bolder and the same size as the largest text used in the TPS.

59 C.3 Marking for enhanced security Technical product document sets, prepared in accordance with the requirements of this clause in addition to those of BS 8888, shall be identified by the addition of the suffix /D to the number of this standard, i.e. BS 8888/D, in a prominent location. NOTE The marking of a technical product document with the number of this standard and the suffix /D, constitutes a claim that the appropriate requirements of all relevant cross-referenced standards, in addition to the requirements directly stated in BS 8888 and in Annex C, have been met. Annex D (informative) Key differences between BS 8888 geometrical tolerancing and ASME Y14.5 geometric dimensioning and tolerancing (GD&T) D.1 Introduction The standards currently cross referenced from BS 8888 have been the subject of extensive review and revision during recent years and this work still continues. Whilst working on these revisions attempt is made to bring about harmonization between ISO standards and existing ASME standards in the Y14.5 series but differences still remain. Some of these differences are of a minor nature or are self evident but others involve indications that are the same or very nearly so but which are interpreted differently between the two systems, giving rise to significant difference in outcome in some cases. This annex sets out to identify and analyse the differences between the systems, whilst making no claim as to which might be the more accurate in any particular application. However, it should be noted that where conformance to BS 8888 is claimed, it is implicit that the interpretations contained in the ISO system will apply. The differences addressed in this annex are not considered to be exhaustive and where the precise meaning of a particular requirement is critical to the performance of the workpiece to be specified, the applicable ISO standards should be consulted directly. D.2 Applicability of standards If provisions from Y14.5 are to be invoked in a TPS prepared in accordance with BS 8888, the relevant Y14.5 cross reference shall be specifically identified at the point of application. By default the rules contained in the relevant ISO standards apply. BSI

60 54 BSI 2006 D.3 Exclusion of surface texture The ISO Standards comprising BS 8888 do not, currently, specify whether surface texture should be included or excluded when geometrical requirements are evaluated. However, the application of BS 8888 requires that surface texture be excluded by the use of appropriate filtering techniques. COMMENTARY ON D.3 COMPARISON WITH Y14.5 ASME Y14.5.1M, which can be taken as an integral part of Y14.5 containing mathematical definitions of the Y14.5 principles, states that all requirements apply after application of the smoothing functions defined in B46.1:1985, i.e. surface texture has to be disregarded when evaluating workpieces using Y14.5 and thus is similar to the position taken in BS D.4 Definition of datums Where a specified datum is of a form that allows the workpiece to rock when brought into contact with it (e.g. if the datum feature is a convex surface) the requirement applied through the application of BS 8888 is to equalize the rock such that an average position and orientation are used as the datum. Each requirement relating to the specified datum shall be evaluated individually to the same average datum. NOTE This rule is currently under revision to introduce more mathematical rigour but the intention of the rule will remain the same. COMMENTARY ON D.4 COMPARISON WITH Y14.5 Y14.5 introduces the concept of candidate datums instead. This concept allows that every position that an unstable datum can rock to (with some limitations) is a valid candidate datum. A set of candidate datum reference frames can be derived for each set of requirements that are referenced to the same datum system, using the same precedence and the same material conditions. These sets of requirements are, by default, evaluated simultaneously to each candidate datum reference frame. If there exists a candidate datum reference frame where all the requirements are fulfilled, the workpiece is acceptable with regard to the requirements. These two sets of rules can result in substantially different conclusions especially if the form error of the datum feature is substantial. In general, the Y14.5 system accepts more workpieces as the form error of the datum feature increases. There are, however, examples where workpieces accepted under the applied BS 8888 (ISO) rules were subsequently ejected upon application of the Y14.5 rules, so assumptions should not be made. Attention is drawn to the fact that no measuring instrument currently available will evaluate workpieces strictly in accordance with either set of rules. D.5 Size requirements The ISO System of limits and fits, defined in BS EN , can be invoked by using the defined tolerance codes (e.g. h7 for a shaft and K8 for a hole). BS EN , in turn, relies upon ISO/R , which defines the inspection of workpieces for size requirements when the ISO tolerance codes are used.

61 ISO/R defines a system of hard gauges that are to be used when verifying size tolerances. In this system, an allowance is made for gauge wear to the extent that in an extreme case a gauge may wear beyond the tolerance limit by up to 30% of the tolerance and still be useable. This means that workpieces can be up to 30% out of tolerance on the maximum material size (small hole or large shaft) and still be acceptable under the ISO limits and fits system. Additionally, the tolerance zones for hard gauges are located symmetrically around either the tolerance limit that the gauge is intended to test (minimum material side) or the wear limit (maximum material side), allowing the gauge to be outside its limit by half its tolerance. The tolerances given in BS EN are, therefore, not the real tolerances. These are derived adding the tolerances given in ISO/R to those of BS EN The need for this can be avoided by specifying the tolerance explicitly instead of applying the tolerance codes but this requires an indication of the size definition (e.g. envelope requirement), to ensure that the requirement is defined on the actual workpiece. D.6 Tolerancing principle The ASME Y14.5 standard uses the Principle of Dependency (aka the Envelope Principle), invoked through Rule #1, for all features-of-size where only a tolerance of size is specified. The envelope of perfect form also applies to features-of-size which have additional geometrical form tolerances (such as flatness or circularity) applied. There are some exceptions to Rule #1: 1) It does not apply to stock materials (bar stock, sheet, tubing, etc.). 2) It does not apply to flexible parts subject to free state variation in the unrestrained condition. 3) It does not apply to features-of-size which have a straightness tolerance applied to their axes or median planes (by implication, this would also be the case where features-of-size have a flatness tolerance applied to the median plane, although the standard does not state this). 4) It may be overruled where a feature-of-size has a specified relationship between size and geometrical tolerances (by use of the m or l modifier in the geometrical tolerance). 5) It may be overruled with a statement such as PERFECT FORM AT MMC NOT REQD placed by a feature-of-size. D.7 Features-of-size BS 8888 and ISOs Cylindrical surfaces Spherical surfaces Two parallel, opposed surfaces A cone A wedge ASME Y14.5:1994 Cylindrical surfaces Spherical surfaces Two parallel, opposed surfaces Two opposed elements (such as the ends of a slot) BSI

62 Although not stated in either set of standards, the 180 rule, whereby a cylindrical or spherical surface is only considered to be a feature-of-size if its included angle is greater than 180, is universally considered to be good practice. D.8 Tolerance characteristics Tolerance BS 8888 and ISOs ASME Y14.5:1994 Positional j Concentricity/ Coaxiality r Symmetry i Profile k and d 56 BSI 2006 The positional tolerance can be used to control the location of features-of-size and also points, lines and flat planes. This tolerance is known both as a concentricity tolerance and a coaxiality tolerance. The ISO definition uses the term concentricity to describe the situation where the centre point of a feature is located on a datum point or axis, and coaxiality to describe the situation where an axis of a feature is aligned with a datum axis. The concentricity/coaxiality tolerance is a special case of the positional tolerance, which can be used to control the location of the axes or centres of circular, cylindrical, spherical or conical features-of-size in relation to a datum axis or point. The concentricity/coaxiality tolerance can be replaced with a positional tolerance to provide an identical control. The concentricity/coaxiality tolerance, like the position tolerance, can be used with material condition modifiers (m or l ). The symmetry tolerance is a special case of the positional tolerance, which can be used to control the location of the axis or median plane of a feature-of-size in relation to a datum axis. The concentricity/coaxiality tolerance can be replaced with a positional tolerance to provide an identical control. The concentricity/coaxiality tolerance, like the position tolerance, can be used with material condition modifiers (m or l ). The tolerance zones for profile tolerances are generated by placing a theoretical circle (or sphere), with a diameter corresponding to the size of the tolerance, on every point of the theoretically exact profile (or surface) to generate the boundary limits. Where the theoretically exact profile (or surface) contains sharp corners (or edges), the tolerance zone boundary external to the corners (or edges) is radiused. Annotation is currently only defined for symmetrical bilateral tolerance zones. This form tolerance is to be known as roundness. The positional tolerance is only used with features of size. ASME Y14.5 recommends the use of the (d) to control a flat planar surface. This tolerance is known only as a concentricity tolerance. The definition for concentricity was changed in the 1994 version of Y14.5. Concentricity is defined as the condition where the median points of all diametrically opposed elements of a figure of revolution are congruent with the axis or centre point of a datum feature. Although frequently confused with coaxiality, this is different to coaxiality (which should be controlled with a position tolerance, j). Concentricity cannot be used with material condition modifiers (m or l ). The symmetry tolerance was reintroduced to the 1994 version of Y14.5, having been removed from the previous version. Symmetry is defined as the condition where the median points of all opposed or correspondingly-located elements of two or more feature surfaces are congruent with the axis or centre plane of a datum feature. Symmetry cannot be used with material condition modifiers (m or l). The tolerance zones for profile tolerances are generated by a vector offset from the theoretically exact profile (or surface) to generate the boundary limits. Where the theoretically exact profile (or surface) contains sharp corners (or edges), the tolerance zone boundary is extended to give a sharp corner (or edge). Annotation is defined for unilateral and unequal bilateral tolerance zones as well as symmetrical bilateral tolerance zones. This form tolerance is known as circularity.

63 Annex E (informative) BS ISO 1101:1984 to BS ISO 1101:2004 The evolution E.1 Revision of BS ISO 1101:1984 The 2004 revision of BS ISO 1101 was eagerly awaited, having not seen any published development for 21 years. The following is a summary of the significant changes. The 2004 edition saw a change in the title, introducing geometric product specifications (GPS) but continues to major on geometrical tolerancing of form, orientation, location and run-out. It is now a general GPS standard and acts as a signpost to other significant standards. A revised introduction sets out the new format of the standard and introduces revised terms such as roundness for circularity, in an effort to align with other GPS standards and also outlines the process of identifying old terms in parentheses throughout the document. A table has been added which identifies the line types used to illustrate the definition of the rules in Clause 18. An informative Annex A has been included to identify former practices. Annex B has expanded some of the information in the former Clause 3 giving normative information on geometrical deviations and Annex C gives normative references to the GPS Matrix Model. E.2 BS ISO 1101:2004, Amendment 1 An amendment of BS ISO 1101:2004 is presently undergoing ISO TC/213 committee approval. This amendment titled Representation of specifications in the form of a 3D model is being introduced due to the extensive use by industry of 3D models within the technical product specification (TPS) field and the immanent publication of ISO 16792, Technical product documentation Digital product definition data practices, which includes the presentation of annotation applied to 3D models. Existing technical product documentation (TPD) and GPS standards supporting TPS only refer to 2D applications and it has been recognized that there is an urgent requirement to review the existing 2D standards with a view to applicability within the 3D field. It has also been recognized that for some considerable time TPS will exist in 2D or 3D format and most likely as a mixture of both so, in order to promote uniformity, any new specification introduced as a result of a specific 3D application will also be suitable for 2D application. This amendment includes: additional indication of the orientation of a tolerance zone where the interpretation could differ between in a 2D and 3D environment i.e. directional dependent tolerances such as straightness when applied to a view on a 2D drawing; additional supplemental indications; revised application of common zone (CZ); and additional figures showing 3D applications. BSI

64 The following is a summary of the significant proposed changes. NOTE The figures in this annex are under development and are included for purely illustrative purposes. Their usability cannot be guaranteed. Clause 3, Terms and definitions: the following will be added with explanatory notes: 3.2 annotation plane Conceptual plane containing annotation [ISO 16792:2006]. 3.3 intersection plane plane, established from an extracted feature of the workpiece, identifying a line on an extracted surface (integral or median) or a point on an extracted line. 3.4 orientation plane plane, established from an extracted feature of the workpiece, identifying the orientation of the width of the tolerance zone. 58 BSI 2006 Figure E.1 Clause 5, Symbols: reference to BS ISO will be removed from Table 2, Projected tolerance zone. New symbols for median feature C and unequally disposed tolerance W will be added. New symbols for intersection plane B and orientation plane covering parallelism, perpendicularity and symmetry have been added. Clause 6, Tolerance frame will be amended to identify more clearly the compartments of the tolerance frame and also introduce the following subclause: 6.5 If required, indications qualifying the direction of the tolerance zone and/or the extracted (actual) line shall be written after the tolerance frame. See example of indication of orientation of the tolerance zone in [Figure E.1]. Indication of orientation of the tolerance zone Clause 7, Toleranced features will be amended to include an opening paragraph that states: If not indicated using an appropriate modifier, a geometric specification is applied to a toleranced feature, which is a single complete feature. When the toleranced feature is not a single complete feature, see Clause 10. B

65 Additional text and figures illustrating 3D application of tolerances will be added to compliment the existing 2D examples. A new modifier symbol C (median feature) will be added with the following text and figure replacing the existing second indent. When the tolerance refers to the median line or median surface or a median point (defined by the feature so dimensioned), then the tolerance frame shall be either: connected as an extension of the dimension line. connected to the feature by a leader line terminating with an arrow head pointing directly at the surface, but with the addition of the modifier symbol placed to the right hand end of the second compartment of the tolerance frame (see [Figure E.2]). Figure E.2 Use of the median feature Clause 8, Tolerance zones: 8.1 will be replaced with the following text and figures (existing figures remain unchanged). The tolerance zone is positioned symmetrically from the exact geometrical form, orientation, or location, unless otherwise indicated (see 10.3). The tolerance value defines the width of the tolerance zone, and this width applies normal to the specified geometry (see examples of Figures 16 and 17) unless otherwise indicated (see examples of Figures 18 and 19). The tolerance value is not variable along the considered feature length, unless otherwise indicated either by: a graphical indication, defining a proportional variation, between two specified values, along two specific locations on the considered feature. The start and end locations where the tolerance value varies are identified by two letters separated by an arrow (see [Figure E.3] and 12.2 for restricted parts of a feature). The values are related respectively with the letters indicated over the tolerance frame and their corresponding specified location on the considered feature (e.g. in Figure 19X, the value of the tolerance is 0,1 for the location J and 0,2 for the location K). By default, rule of proportionality is relevant to the curvilinear coordinates; a specific company indication, when the variation is not proportional. A BSI

66 Figure E.3 Restricted parts of a feature J K K J 8 Subclause 8.5 will be replaced by the following text and figures. 60 BSI 2006 Figure E.4 Where a common tolerance zone is applied to several separate features, this common requirement shall be indicated by the symbol CZ for common zone following the tolerance in the tolerance frame (see examples of [Figure E.4 and Figure E.5]). A common tolerance zone is defined by all related individual tolerance zones, with a common geometrical characteristic and the same tolerance value, located and orientated between each other. Example of a common tolerance zone Where CZ is indicated in the tolerance frame, all the related individual tolerance zones shall be located and orientated between each other using either implicit (0 mm, 0, 90, etc.) or explicit theoretically exact dimensions (TED).

67 Figure E.5 Example of a common tolerance zone Figure E.6 Clause 9, Datums: complementary figures and text will be added to 9.2, 9.3 and 9.4 to illustrate 3D application of datums. Clause 10, Supplementary indications: the following text and illustrations will be added to 10.1 covering 3D application of the all round symbol. In 3D annotation, if a profile characteristic is applied to the entire outline of the cross-sections (intersection between the annotation plane required and the surface) or if it is applied to the entire surface represented by the outline, it shall be indicated by using the symbol all around (see [Figure E.6]). This indication does not involve the entire workpiece, but only the surfaces represented by the defined outline and identified by the tolerance indication (see [Figure E.6]). Examples of the use of the all around symbol A new subclause 10.2, Indication of unequally disposed tolerance zone will be added. The following text and figures will be added to explain the new rules. If the tolerance zone is not centered on the theoretically exact geometrical form, then this unequally disposed tolerance zone shall be indicated using the U modifier as shown in [Figure E.7]. BSI

68 Figure E.7 Unequally disposed tolerance zone indicator 62 BSI 2006 The extracted (actual) surface shall be contained between two equidistant surfaces enveloping spheres of defined diameter equal to the tolerance value, the centres of which are situated on a surface corresponding to the envelope of a sphere in contact with the theoretically exact geometrical form and whose diameter equal to the absolute value given after U with the direction of the shift indicated by the sign, plus indicating out of the material and minus into the material. The existing 10.2 will become 10.3, Indications for screw threads. Clause 12, Restrictive specifications: complementary figures and text will be added to 12.2 to illustrate 3D application. The following text and figures will be added to introduce the between concept. If a tolerance is applied to one identified restricted part of a feature or to contiguous restricted parts of contiguous feature(s), but does not apply to the entire outline of the cross-sections (or entire surface represented by the outline), this restriction shall be indicated using the symbol (called between ) and by identifying the start and the end of the considered toleranced zone. The between symbol is used between two letters that identify the start and the end of the considered toleranced zone. This zone (compound toleranced feature) is elaborated from all segment or area between the start and the end of the identified features or parts of features. In order to clearly identify the tolerance zone, the tolerance frame shall be connected to the compound toleranced feature by a leader line starting from either side of the frame and terminating with an arrowhead on the outline of the compound toleranced feature (see example of [Figure E.8]). The arrowhead may also be placed on a reference line using a leader line to point to the surface.

69 Figure E.8 Example of the use of the compound toleranced feature Interpretation: The long dashed-dotted line (in the 3D Figure) represents the considered toleranced features. Surfaces a, b and c are not considered in this specification. Figure E.9 In order to identify the start and end of the compound tolerance feature, they shall be indicated in one of the following ways: Indicating the start and end of the compound toleranced feature J J Edge Location using a TED J R Radius edge Use of ISP basic symbol NOTE If not indicated (using, e.g., a TED) the edge of the feature is included. If the tolerance value is variable along the considered compound toleranced feature, the symbol called from ) shall be used instead of between. See Clause 8. If a same specification is applicable to a set of compound toleranced features, this set can be indicated above the tolerance frame, one above the other (see example in [Figure E.10]). J BSI

70 Figure E.10 Indicating a common set of toleranced features L J M K J K L M 64 BSI 2006 Figure E.11 If all the compound toleranced features that are in this set are defined identically, it is possible to simplify the indication of this set, using the n x indication (see 6.2). In this case the indication of the letters identifying the start and end shall be placed into a square bracket. The rule defined in Clause 8 regarding the common zone indication is applicable to define a common compound tolerance zone (see example in [Figure E.11]). Indicating a common compound tolerance zone Clause 13, Projected tolerance zone: the whole of this clause has been rewritten to include additional symbology and 3D applications and will be replaced by the following: The use of projected tolerance provides for the modification of the default toleranced feature used for the orientation or location of a GPS, by enabling the toleranced feature to become a portion of an extended feature, which is outside of the workpiece.

71 The extended feature shall be constructed from an associated feature relative to the real integral surface and is the associated feature or its derived feature. The toleranced feature is thus a portion of the extended feature (see Table 3). NOTE The association criterion is by default, minimizing the distance between the integral feature and the associated feature, which is constraint tangent outside of the material. Table 3 Toleranced feature with the projected tolerance modifier Nominal feature to which the leader line from the tolerance frame points Toleranced feature A cylinder An axis of a cylinder A plane A median plane Portion of the associated cylinder Portion of the axis of the associated cylinder Portion of the associated plane Portion of the median plane of two associated planes constraint parallel The use of the projected tolerance concept shall be indicated by the use of the symbol p after the tolerance value in the second compartment of the tolerance frame, see Figure 47A a) and b). The limits of the relevant portion of this extended feature shall be clearly defined and shall be indicated either directly or indirectly, as follows: When indicating the projected tolerance directly on a virtual integral feature representing the extended feature to be considered, it shall be represented by a chain thin double-dashed line in the corresponding drawing view, and the length of the extension shall be dimensioned with a theoretically exact dimension (TED) with the symbol p prior to the value. See [Figure E.12a)]. When indicating indirectly the length of the projected toleranced feature, the value shall be specified within square brackets [ ] after the symbol p in the tolerance frame. See [Figure E.12 b)]. In this case the representation of the extended feature with a chain thin double-dashed line shall be omitted. However, the side of the part to which the projected tolerance applies shall be clearly specified by an arrow above the tolerance frame, see [Figure E.13]. BSI

72 Figure E.12 Two different ways of indicating a GPS with projected tolerance modifier a) Direct indication of the length of the extension by a TED b) Indirect indication of the length of the projected toleranced feature in the tolerance frame Figure E.13 Explanation of the direction of the extended feature 66 BSI 2006 Figure E.14 a) Reference surface defining the starting of the toleranced feature b) Direction of extension of toleranced feature The reference surface, defined by the intersection of a plane and the considered feature, is, by default, the origin for the extended feature. If the portion of the extended feature is displaced from the reference surface by an offset, the offset shall be indicated. When directly indicated, the offset shall be specified by a theoretical exact dimension (TED), see [Figure E.14]. When indirectly indicated, the first value after the modifier corresponds to farthest extent of the extended feature and the second value (offset value), which is preceded by a minus sign, corresponds to the nearest extent of the extended feature (the length of the extended feature corresponds to the difference between these two values), see [Figure E.15]. Example of direct indication of a projected tolerance with an offset

73 Figure E.15 Example of indirect indication of a projected tolerance with an offset j i c k 0,2 P [32-7] e f a g h d b Key a) Extension of the outline b) Reference surface c) Leader line connected to the tolerance frame d) Associated reference surface e) Integral surface f) Associated feature g) Length of the projected toleranced feature, in this case L = 25 h) Offset of the projected toleranced feature from the reference surface, in this case 7 mm i) projected toleranced feature j) modifier defining that the tolerance applies to a portion of an extended feature and is limited by the information g) and h) k) Indication defining that the type of the toleranced feature is a median feature NOTE The associated reference surface, indicated with d) in the key, will require additional definition by the indication of a datum system to make the requirement unambiguous. If the value of the offset is zero, the indication is omitted, see [Figure E.13]. The modifier p may be used with other types of modifier as appropriate, see [Figure E.16 and Figure E.17]. BSI

74 Figure E.16 Example of the use of projected tolerance zone together with the median modifier Key a) Extension of the outline b) Reference surface c) Leader line connected to the tolerance frame 68 BSI 2006 Figure E.17 d) Modifier defining that the tolerance apply to a portion of an extended feature and is limited by the subsequent information e) e) Length of projected toleranced feature, in this case 25 f) Modifier defining that the type of the toleranced feature is a median feature Example of the use of projected tolerance zone together with a common zone modifier Clause 18, Definitions of geometrical tolerances: an extra column will be added to the Indication and explanation section of the table to illustrate 2D and 3D application of the symbols separately.

75 Annex F (informative) Technical product specification Geometrical product specification (GPS) F.1 Introduction Over the course of the 20th Century, with the advent of mass production, the need to be able to manufacture parts to a specification with a high degree of repeatability became more important than ever before. This led to a formalization of the methods used to specify workpieces through the use of engineering drawings with dimensions and tolerances, and the development of new methods to specify geometrical characteristics (geometrical tolerancing) and surface texture (i.e. roughness values). Most industrialized countries developed national standards to govern the methods used for engineering specifications, giving rise to the much loved BS 308 in the UK, and the ANSI Y14.5 (now ASME Y14.5) standard in America, as well as similar standards in many other countries. The evolution and development of these methodologies has continued throughout this period and into the 21st Century, with standards being added, extended and revised accordingly. Under the ISO banner, the standards organizations from many different nations have worked together to develop and harmonize the different standards used for engineering specifications, and to encourage a common approach, with a view to improving communications and addressing the needs of a more global economy. As a consequence of the way in which methodology has evolved and developed over the last 80 or so years, there are many areas in which the standards for engineering specifications are (or at least have been) ambiguous, inadequate, incomplete and even contradictory. These issues have been highlighted by several developments, including: improvements to the accuracy with which a workpiece can be manufactured; improvements to the accuracy with which a workpiece can be measured or inspected; the trend in the developed world to focus on design and assembly, subcontracting component manufacture to suppliers who are often overseas, and might not speak the same language (this trend in particular has removed the option of the informal communication or understanding that would often exist between design and manufacturing when they were neighbouring departments in the same company); and the requirements of CAD, CAM and CAQ system architects for formal mathematical definitions of all specification and verification operations that can be coded into software. In response to this situation, ISO initiated a project in the early 1990s with the aim of developing a coherent, comprehensive and complete system for the specification of workpiece geometry. This system is called geometrical product specification (GPS). BSI

76 As its name suggests, GPS is concerned with the geometry of parts; it is not concerned with material properties or operating conditions. Specifically, GPS is concerned with the specification and verification of sizes, shapes and surface characteristics of a workpiece to ensure functional requirements are met. GPS is a new approach to product specification; but it builds on existing tools, and particularly the use of datums, geometrical tolerancing and surface texture tolerancing. GPS systematizes and extends these existing tools into a new methodology. F.2 Key concepts Figure F.1 70 BSI 2006 F.2.1 Different worlds or models The GPS approach is based on the concept that any given workpiece exists in several different worlds, or as several different versions, at the same time (see Figure F.1). There is the specification model, produced by the designer to represent the design intent or functional requirement; there is the actual manufactured workpiece; and there is the verification model, representing the metrological data extracted from the model by various measurement processes. The verification model is compared with the specification model in order to establish whether the workpiece complies with its specification. Model of the relationship between specification, verification and the actual workpiece Designer Function Specification Graphical representation Production engineer Workpiece generation Comparison Real workpiece Metrologist Extracted data/signal Measured values

77 F.2.2 Specification and verification One of the objectives of GPS has been to strengthen and clarify the relationship between the specification process, where the workpiece geometry is defined, and the verification process, where the workpiece is checked against its specification. It clearly makes sense for the inspection or verification process to inspect, as directly as possible, whatever quantity has been specified. Where the inspection process cannot directly check what has been specified, then there is greater scope for errors, or greater uncertainty in the process. When a workpiece is inspected or verified, a number of processes take place (see Figure F.2). These processes have been classified as partition, extraction, filtration, association, collection and construction. Much of the time, these processes are not consciously classified, it is just the way we do things. Figure F.2 The link between design intent and metrology Drawing Workpiece Extraction Association Partition: a workpiece is partitioned, or broken down, into a number of real, integral features (actual surfaces). In other words, we tend to think of, and deal with, workpieces as a collection of individual surfaces flat surfaces, cylindrical surfaces, curved surfaces, etc. Extraction: having partitioned a workpiece into a number of real, integral features, we need to extract some data from them, so that they can be quantified, measured or located. The real, integral feature can be defined as a set of an infinite number of points, defining the surface that separates the workpiece from its surroundings within the extents of that particular feature. When measuring or sampling a real integral feature, we cannot measure or sample an infinite number of points, we have to compromise and sample a finite number. The extracted, integral feature thus consists of a finite number of points BSI

78 Filtration: in practice, it is found that extraction on its own is not sufficient to give a useful set of data representing the integral feature under consideration. In addition to extraction, some filtering or smoothing of the data is usually necessary, to remove noise, and unwanted detail. Association: having obtained an extracted model of the real, integral feature, consisting of a filtered and finite number of points, it may be that the verification process is required to check the form (i.e. straightness), orientation (i.e. perpendicularity) or location of a derived feature (axis, median plane or centre point) based on that integral feature. In order to do this, a theoretically perfect geometrical form, corresponding to the nominal form in the specification model (i.e. a perfect cylinder, perfect set of parallel opposed planes, perfect sphere, cone or wedge) has to be fitted to, or associated with, the extracted data. This is known as the associated integral feature. Collection: in additional to the above operations, features sometimes need to be treated as a group or pattern of features. Groups or patterns of holes are a common example of this. Collection is the process of grouping these features together. Construction: sometimes tolerances may be applied to features which are dependent on, or resultants of, other features. A construction operation is used to determine the toleranced feature. For instance, straightness may be applied to an edge, the edge being defined as the intersection of two planes. The edge is constructed from the two extracted planar features. 72 BSI 2006 F.2.3 The operator principle and the duality principle The fact that these processes of partition, extraction, filtration, association, collection and construction take place during verification is of some consequence to the specifier. For instance, the designer or specifier can apply a flatness tolerance to a surface. In theory, that flatness requirement is applied to the entire set of an infinite number of points which comprise the real, integral surface. However, the verifier is going to check an extracted, integral surface, consisting of a finite number of points, which has been filtered to remove noise and unnecessary detail. The density of the extracted data, and the wavelength of the filters which have been used, will clearly influence the results. For this reason, the GPS approach requires these processes to be taken into account when specifying a workpiece requirement to the same extent that they will be required for its verification. This concept, that the verification process and the specification process should mirror each other, or be duals of each other, is known is the duality principle (see Figure F.3).

79 Figure F.3 The duality principle SPECIFICATION OPERATOR VERIFICATION OPERATOR "SKIN MODEL" Geometrical representation "REAL SURFACE" Set of physically existing features Operation partition extraction filtration association collection construction Difference contributes to uncertainty Operation physical partition physical extraction filtration association collection construction MEASURAND Characteristics specification COMPARISON FOR CONFORMANCE MEASURED VALUE Characteristics To some extent this already happens. Partition takes place automatically, as workpieces are modelled, or drawn, as a collection of discrete features. Collection also takes place routinely, as dimensions, tolerances or notes are used to indicate when several features are to be treated as a group or pattern of features. Construction again takes place quite automatically, as edges and vertices appear where defined surfaces meet and intersect. The processes of extraction and filtration, however, are normally left to the discretion of the verifier. The designer specifies the requirement for a real surface, the verifier checks it on the extracted surface, and the verifier will choose a sampling density and filtering function based on factors such as experience, informal understanding of the design requirements, in-house procedures, time available, equipment capabilities and limitations, mood, whim, etc. Under the GPS approach, this will change. The specifier will be required to define the sampling density and filtering function. BSI

80 The process of association is also not normally considered by the designer or specifier. Association will have to take place if the verifier is required, say, to use the axis of a shaft as a datum, or to evaluate a positional tolerance on a hole. How the theoretically perfect associated feature is fitted to the extracted feature is again left to the verifiers discretion. Mathematically, there are several ways in which this association can take place, including, for instance, the least squares method, the maximum inscribing method, and the minimum circumscribing method. Again, under the GPS approach, the appropriate method of association will need to be defined by the specifier. Thus each element of the specification will contain its own definitions for the processes of extraction, filtration and, where appropriate, association. Each specification element, which is known as a specification operator, is, in effect, a virtual measurement procedure, containing all the information that may be required for its verification (including datums, sampling densities, filtering values, and association methods). The verification operator is the physical implementation of that virtual measurement procedure defined in the specification. This is known as the operator principle. The specification operator is not intended to dictate the verification method, merely to provide all the information that will be required in order that it may be verified. So far, this approach has only been fully implemented in the annotation system used for defining surface texture. The annotations, definitions and values required to implement the GPS approach with geometrical tolerancing are still under development, and standards dealing with the different types of tolerance characteristic are gradually starting to appear. 74 BSI 2006 F.2.4 The default principle This new approach will, at first glance, greatly increase the work load on the specifier, and greatly increase the volume of annotation required to properly define a workpiece. In order to avoid both of these burdens, default values and methods are under preparation for the processes of extraction, filtration and association. Where the default values or methods are to be used, they need not be marked on the annotation. This is known as the default principle. For example, if the designer specifies a location tolerance for a hole, the GPS approach requires the specification to include data on which association method, sampling density, and filtering techniques or values should be used. However, the GPS approach will also provide default values for each of these items. The specifier will only produce annotation for these items where a value or method other than the default is required. This means that in many, and probably almost all, cases, the full and complete annotation will appear no different to the current annotation. The only difference will be that the values and methods to be used when verifying the requirement will be fully and unambiguously defined (by the default values and methods), and not left to the discretion of the verifier.

81 F.3 Uncertainty F.3.1 F.3.2 F.3.3 Introduction A fundamental concept in the GPS system is that of uncertainty. The concept of uncertainty is not new; it is an established fact of metrology. The uncertainty associated with a measurement can be thought of as representing how good the measurement is. If several measurements are taken of a length with a ruler, each measurement will be slightly different. Consistency is achieved by recognizing the limitations of accuracy that can be achieved with a particular technique or piece of equipment, so no one would attempt to measure to accuracies of 0.01 mm with a ruler. The uncertainty associated with the ruler is a parameter that represents the range of possible values that could reasonably be obtained when measuring any given length with the ruler this could be given as a simple value (perhaps 0.2 mm in this case), or a percentage, or a statistical quantity. Metrology equipment normally includes uncertainty values with the other data in its specification. The GPS system extends this concept of uncertainty to the specification model as well as the verification model, and considers three different types of uncertainty. Correlation uncertainty Correlation uncertainty quantifies how well the workpiece specification correlates to the functional requirements of the workpiece. This uncertainty is the responsibility of the designer. Some of this uncertainty can be reduced or eliminated simply through professional competence, but some of it is inevitable. For instance, FEA techniques may be used to calculate the geometrical form of a structural component, but these calculations are approximations, and the operating conditions and material characteristics which the calculations are based on are themselves approximations and simplifications of the real-life situation. Specification uncertainty Specification uncertainty arises from the range of possible interpretations of a specification. This uncertainty is again the responsibility of the designer. As with correlation uncertainty, some of this uncertainty can be eliminated through professional competence (ensuring specifications are complete, effective use of datum systems, etc.). Specification uncertainty can arise not only from poor design or specification, but also from inherent ambiguities or incompleteness in standards. For instance, ISO standards do not state whether surface texture should be included or excluded when checking for geometrical variation. This incompleteness in the standard may result in a range of possible interpretations of a single tolerance specification. The manufacturer is entitled to choose any legitimate interpretation to work to. BSI

82 F.3.4 Measurement uncertainty (attributed to the metrologist) Measurement uncertainty has two aspects. The first is termed method uncertainty, and this is to do with differences between the specification operator and the verification operator, in other words, this is to do with what measurements are taken. If the verification operator is a perfect implementation of the specification operator, there is no method uncertainty. The second classification is termed implementation uncertainty, which arises from deviations in the implementation of the verification operator, so this would include operator error, faulty equipment, etc. 76 BSI 2006 F.3.5 Making use of uncertainty Identifying sources of uncertainty has practical benefits, and quantifying uncertainty is a necessary aspect of specifying and verifying complete and unambiguous definitions of workpiece geometry. Identification of the sources of uncertainty can help with the allocation of resources. For instance, if correlation uncertainty is large, because component geometry is based on assumptions and highly approximate calculations, there would be little benefit in investing in highly accurate (and expensive) inspection equipment. Resources would be better targeted towards more accurate computer modelling and simulation, or acquiring more test data. When values can be assigned to measurement uncertainty, this can then be taken into account when verifying the workpiece. If checking to see whether tolerance limits have been complied with, then the each tolerance limit should be reduced by the amount of measurement uncertainty associated with the procedure. Where checking to see whether tolerance limits have been violated, each tolerance limit should be extended by the amount of measurement uncertainty associated with the procedure. Measurement uncertainty always counts against the verifier. F.4 The GPS standards matrix GPS is a procedure for defining the shape (geometry), dimensions and surface characteristics of a workpiece in a manner that ensures optimum functioning of that workpiece. The procedure includes definition of the dispersion around the optimum within which the intended function will still be satisfactory. The manufacturing process will, nevertheless, produce workpieces that are not perfect, in that they show some deviation from the defined optimum and from each other. When comparing a workpiece with its specification, it is necessary to relate the following: the workpiece conceived by the designer; the workpiece as manufactured; and the workpiece as measured. Standards developed in this field provide the fundamental rules for GPS, such as basic definition, symbolic representation and principles of measurement.

83 Several categories of standard relate to the concept. Some of these deal with the fundamental rules of specification, whilst others provide global principles and definitions. A third group addresses directly the various geometric characteristics such as size, distance, angle, form, location, orientation and roughness. The concept includes workpiece characteristics relating to different types of manufacturing process, together with the characteristics of specific machine elements (see Figure F.4). The application of GPS principles will only deliver benefit to their full potential if applied throughout the development of a product, i.e. in design, manufacturing, metrology and quality assurance. BSI

84 Figure F.4 The GPS matrix model The global standards GPS standards or related standards that deal with or influence several or all 'general GPS chain' standards 78 BSI 2006 The fundamental GPS standards General GPS matrix General GPS chains of standards 1 The size chain 2 The distance chain 3 The radius chain 4 The angle chain 5 The form of line (independent of a datum) chain 6 The form of line (dependent on a datum) chain 7 The form of a surface (independent of a datum) chain 8 The form of a surface (dependent on a datum) chain 9 The orientation chain 10 The location chain 11 The circular run-out chain 12 The total run-out chain 13 The datums chain 14 The roughness profile chain 15 The waviness profile chain 16 The primary profile chain 17 The surface defects chain 18 The edges chain Complementary GPS matrix Complementary GPS chains of standards A. Process specific, tolerance standards A1 A2 A3 A4 A5 A6 A7 The machining chain The casting chain The welding chain The thermal cutting chain The plastics moulding chain The metallic and inorganic coating chain The painting chain B. Machine element, geometry standards B1 B2 B3 The screw thread chain The gears chain The splines chain

85 Annex G (informative) Technical product realization UK development G.1 BS 8888 Rationale BS 8888 is drafted with the sole objective of enabling this improvement in technical product specification on the basis of the application of established and developing International Standards. The prime objective of BSI Technical Committee TDW/4, Technical, product specification Methodology, presentation and verification, is to ensure that the necessary tools to enable the preparation of detailed, accurate specifications, are available. Its activity covers seven complimentary generic subject areas: a) methodology for design implementation; b) geometrical product specification; c) graphical representation (engineering drawings/diagrams and 3D modelling); d) verification (metrology and precision measurement); e) technical documentation; f) electronic formats and controls; g) related tools and equipment. The committee is responsible for identifying and evaluating requirements for British Standards relating to the preparation, presentation and validation of technical specifications and for the drafting of any such standards for which a genuine need has been established. The programme of work addresses the requirements for standardization in technical specification, at all stages from the preparation of design concepts for physical realization to the validation of finished products. All such projects are based on existing or developing ISO Standards (particularly those of ISO/TC 10 and ISO/TC 213), where such standards exist. The committee is responsible for channelling UK expertise into relevant ISO projects to ensure that their outcome meets UK requirements to the best possible extent. This principal applies irrespective of the programme of ISO implementation within the European Standards Organization (CEN). Where appropriate International Standards/Projects do not exist, TDW/4 undertakes the responsibility for the drafting of any necessary British Standards or Technical Reports. This is done with a view to their subsequent introduction to the ISO programme, where appropriate. Given the importance of this subject area in both secondary and further education, The UK Technical Committee (TDW/4) takes an active interest in the preparation and promotion of educational support materials for schools, colleges and industrial training. BSI

86 80 BSI 2006 G.2 Technical product documentation The presentation aspects of TPS are primarily the province of ISO/TC 10, Technical product documentation, which has the brief to develop, co-ordinate and maintain International Standards for technical product documentation (TPD), including technical drawings manually produced or computer based, for technical purposes throughout the product life cycle in order to facilitate preparation, management, storage, retrieval, reproduction, exchange and use. Although this committee is founded on the more traditional discipline of engineering drawing, its remit has been extended to include the presentation of all forms of specification for technical products, whatever the media selected to carry that specification. In particular, this includes the graphical representation and annotation of the output of 3D modelling programmes. ISO/TC 213 is the international, standards technical committee responsible for the development of GPS in order to provide an integrated system for specification and verification of workpiece geometry (see Annex F). The work of ISO/TC 10 is closely linked to that of ISO/TC 213 by virtue of their joint application in TPS. However, it is important to have a clear understanding of the functional relationship between the various elements of the TPS and of their relative significance to the effectiveness of the specification. Figure G.1 provides a useful graphical representation of the relationships between the elements of the TPS.

87 Figure G.1 The relationship between the elements of a technical drawing G.3 Technical product realization The TPR concept. Having gained practical experience in the application of BS 8888 during the six years since its introduction in 2000, the BSI Technical Committee has also had the opportunity to address some of the misconceptions occasionally expressed by practising designers, engineers and metrologists. One of these, concerns the stage of manufacture at which BS 8888 should be implemented. There are, not infrequently, suggestions that since this standard sets out requirements for a specification, it is the actual manufacturing stage that will be most affected by its provisions. This is far from being a true picture. BSI