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Engineering

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Part 2: A guide for highereducation to as 8888:2000,Technical product documentation

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Contents

Contents Page

Foreword 1Scope 2Listoffigures,tablesanddrawings... ..., ,. """" ..41 Layout of drawings 92Scales 133Projection 144Linesandarrows 175Letteringandnumerals 226Views 247 Sections and sectional views 288Symbolsandabbreviations 359Itemreferences 3710 Representation of features 3911 Representation of components 4412Dimensioning 4913Dimensioningfromacommonfeature 5814Tolerancing ', 7115Methodsofindicatingsurfacetexture.., 10116Diagrams 10917 Microcopying and storage 112Annex A (informative) Correspondence between BS 308-1 and BS 8888. . . . . . . . . . . . . . . . 116Annex B (informative) Examples of mechanical engineering drawings. . . . . . . . . . . . . . . . . 119Annex C (informative) Approaches to 3-D modelling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Annex D (informative) A model of geometric product specification (GPS) and verification. . 122AnnexE(informative)BS8888kits 128Annex F (informative) Examples of the application of different types of line. . . . . . . . . . . . 130Bibliography 139Index 142

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1 Layout of drawings

1.1 General

This clause gives guidance on best-practice in the layout of pre-printed technical drawings, includingthose produced by computers.

1.2 Drawing sheets

The "A" series of drawing sheets, shown in Figure 1, is normally used. The drawing area and titleblock should be within a frame border. In general, material within the frame border forms part ofany contract requirements.

A4 = 210 mm x 297 mmA3 = 297 rom x 420 mmA2 = 420 mm x 594 mmAl =594 rom x 841 romAO = 841 mm x 1189 romThe sides of all sheets are in the ratio 1: ff

AO is normally one square metre in area and forms the basisof the series.

Figure 1 - Relationship of the "A" sizes

1.3 Title block

The title block for paper sizes AOto A3 should be situated in the bottom of the sheet and extend tothe lower right-hand comer of the frame. Only sheets positioned horizontally are permitted for theseformats. For A4 size paper, the title block is situated in the shorter (lower) part of the drawing space.Only sheets positioned vertically are allowed for this format. The direction of reading of thedrawings is equal to that of the title block.

Drawings should include the following basic information in the title blocks:

- name;

- date;

- projection symbol (see Clause 3);

- original scale (see Clause 2);- title;- drawing number.

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1.4 Borders and frames

Borders enclosed by the edges of the trimmed sheet and the frame limiting the drawing space shouldbe provided with all sizes. The border should be 20 mm wide on the left edge, including the width ofthe frame. It can be used as a filing margin. All other borders are 10 mm wide (See Figure 2).

2 4 5 Dimensions in millimetres

3

20

Key1 Trimming mark2 Trimmed format3 Grid reference

4 Frame of drawing space5 Drawing space6 Untrimmed format

Figure 2 - Borders

1.5 Drawing formats

Drawing sheets may be produced in two formats. Portrait format is intended to be viewed with thelongest side of the sheet vertical, see Figure 3a). Landscape format is intended to be viewed with thelongest side of the sheet horizontal, see Figure 3b), Figure 3c) and Figure 3d).

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a)Detail (single part) drawings

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3 PIN2 PUllEY1 BRACJ<ET

ITEM

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d) Assembly drawingFigure 3 - Types of drawings

1.6 Types of drawings

There are different types of drawings, two of which, detail and assembly type drawings, are shownin Figure 3.

NOTE For further information on item referencing see Clause 9.

1.7 Marking

Technical product documentation (TPD) prepared in accordance with the requirements of BS 8888should be marked with the number of the standard, i.e. BS 8888 in a prominent location.

NOTE The marking of TPD with "BS 8888" constitutes a claim that the appropriaterequirements of all relevant cross-referenced standards, in addition to the requirementsdirectly stated in BS 8888, have been met.

If the TPD has been prepared using the independency system of tolerancing, the symbol identifyingthe number of the standard should be supplemented by the letter "I" contained within an equilateraltriangle, as shown in Figure 4.

8S 8888 ~Figure 4 - Method of indicating that the independency system of tolerancing has been used

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Relevant standardsBS EN ISO 5457:1999

BS EN ISO 3098-0: 1998

BS EN ISO 5455:1994BS ISO 7200: 1984BS ISO 9958-1: 1992

BS 8888:2000

Associated clausesClause 2Clause 3Clause 4Clause 9

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DescriptionTechnical product documentation - Sizes and layout of drawingsheetsTechnical product documentation - Lettering - Part 0: GeneralrequirementsTechnical drawings - ScalesTechnical drawings - Title blocksDraughting media for technical drawings - Draughting film withpolyester base - Part I: Requirements and markingTechnical product documentation (TPD) - Specification fordefining, specifying and graphically representing products

DescriptionScalesProjectionLines and arrowsItem references

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1:2 1:5 1:10

1:20 1:50 1:100

1:200 1:500 1:1000

2 Scales

) 2.1 General

Every drawing should be drawn in proportion, i.e. to a uniform scale. The scale used should bestated on the drawing as a ratio, e.g. ORIGINAL SCALE 1:1. The words full size, half size, etc.,should not be used.

2.2 Recommended scales

Recommended scales are as follows:

- For drawings represented full size:

1:1

- On drawings smaller than full size (reduction scales):

- On drawings larger than full size (enlargement scales):

2:1 5:1 10:1

20:1 50:1

2.3 Choice of scales

The scale to be chosen for a drawing depends on the size of the drawing sheet and the size of theobject to be depicted. The scale should be large enough to permit easy and clear interpretation of theinformation. Details that are too small for clear dimensioning in the main representation should beshown in a separate view to a larger scale, see Figure 14.

Relevant standardsBS EN ISO 5455:1995

DescriptionTechnical drawings - Scales

Associated clausesClause 1Clause 4Clause 5Clause 12Clause 13

DescriptionLayout of drawingLines and arrowsLetterings and numeralsDimensioningDimensioning from a common feature

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Projection Symbol

Firstangle E3 (fJThird angle

\!1 E3

3 Projection

3.1 General

In this section only orthographic representations will be defined. Orthographic representations areobtained by means of parallel orthogonal projections. They result in flat, two-dimensional viewssystematically positioned relative to each other.

Other projection methods are reviewed in the standards referenced at the end of this clause.

Either first or third angle projection may be used. Mixed projections on one drawing are undesirable.When a view cannot be conveniently shown in its correct projected position the direction of viewingshould be clearly shown. An arrow and view title may be used, similar to those in Figure 14. Themost informative view of the object to be represented is normally chosen as the principal view (frontview). The principal view usually shows the object in the functioning or manufacturing mountingposition.

3.2 Projection symbols

The system of projection used on a drawing should be indicated by the appropriate symbol given inFigure 5.

Figure 5 - Symbols indicating methods of projection

3.3 Recommended proportions

Recommended proportions for projection symbols are shown in Figure 6.

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Figure 6 - Recommended proportions for projection symbols

3.4 Examples of first and third angle projection

Examples of first and third angle projection are shown in Figures 7 and 8. It is rarely necessary toshow all six views.

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Figure 7 - Example of first angle projection

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Figure 8 - Example of third angle projection

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Relevant standardsBS EN ISO 5456-1:1999BS EN ISO 5456-2: 1999

BS EN ISO 5456-3:1999

BS EN ISO 10209-2:1996

BS ISO 128-30:2001

BS ISO 128-34:2001

Associated clausesClause 5Clause 6

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DescriptionTechnical drawings - Projection methods - Part 1: SynopsisTechnical drawings - Projection methods - Part 2: OrthographicalrepresentationTechnical drawings - Projection methods - Part 3: AxonometricrepresentationsTechnical product documentation - Vocabulary - Part 2: Termsrelating to projection methodsTechnical drawing - General principles of presentation -Part 30: Basic conventions for views (Informative)Technical drawing - General principles of presentation -Part 34: Views on mechanical engineering drawings.

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DescriptionLettering and numeralsViews

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4 Lines and arrows

4.1 General

A line is defined as a "geometric object, the length of which is more than half of the line width,which connects an origin with an end in any way", e.g. straight, curved, with or withoutinterruptions.

4.2 Presentation

An lines should be uniformly black, dense and bold. Lines should be all in pencil or all in black ink.For a more detailed guidance on hand produced and computer aided design (CAD) original drawingssee Clause 1.

4.3 Line width

The width, d, of all types of line should be one from the following series. The choice depends on thetype and size of drawing. This series is based on a commonratio 1:6 ("" 1:1,41) as follows:

0,13 mm; 0,18 mm; 0,25 mm; 0,35 mm; 0,5 rom; 0,7 rom; 1 rom; 1,4 mm; 2 rom.

The widths of extra wide, wide and narrow lines are in the ratio 4:2: 1. The line width should beconstant along the whole line.

The minimum spacing between parallel lines should not be less than 0,7 rom, unless rules to thecontrary are stated in other International Standards.

NOTE In certain cases when computer-aided drawing techniques are used, the spacing oflines on the drawing does not represent the actual spacing, e.g. for the representation ofscrew threads. This fact has to be considered when data sets are established, e.g. for theoperation of machine tools.

4.4 Types of line and their application

Types of line and their application are described in Table 1. Further examples are given in Annex F.

Dashed lines (type E). The dashes should be of consistent length and spacing, approximately to theproportion shown in Table 1. Dashed lines should start and end with dashes in contact with thehidden or visible lines from which they originate, except when the hidden line continues a visibleline. Dashed lines should also meet with dashes at tangent points and comers.

Chain lines (types F, G and H). All chain lines should start and finish with a long dash, but note thelength of the wide dash at the ends of the cutting plane line (type G) and at the changes of direction.

Where centre-lines define centre points they should cross one another at long dash portions of theline.

Centre-lines should extend only a short distance beyond the feature or view to which they apply. Ifrequired for dimensioning they should continue as projection lines. Common centre-lines should notextend across the space between adjacent views. Centre-lines should not stop at another line of thedrawing. Where angles are formed in chain lines, long dashes should meet or cross at comers.

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Line Description Application

A Continuous AI: Visible outlineswide A2: Visible edges

A3: Crests of screw threads

A4: Limit of length of full depth thread

A5: Main representations on diagrams, maps, flowcharts

A6: System lines (structural metal engineering)

A7: Parting lines of mould in views

A8: Lines of cuts and sections

B Continuous BI: Imaginary lines of intersectionnarrow B2: Dimension lines

B3: Projection lines

B4: Leader lines and reference lines

B5: Hatching

B6: Outlines of revolved sections in place

B7: Short centre lines

B8: Root of screw threads

B9: Origin and terminations of dimension lines

B I0: Diagonals for the indication of flat surfaces

B 11: Bending lines on blanks and processed parts

B12: Framing of details

B13: Indication ofrepetitive detailsB14: Interpretation lines oftapered features

B15: Location of laminations

B16: Extension lines

B17: Grid lines

C Continuous C 1: Preferably manually represented termination of partial~narrow or interrupted views, cuts and sections, if the limit is not airregularZ) line of symmetry or a centre line, (see Figure 107 and

Figure 108)

~Continuous D 1: Mechanically represented termination of partial ornarrow straight interrupted views, cuts and sections, if the limit is not a linewith of symmetry or a centreline, (see Figure 101 andzigzagsl),Z) Figure 118)

E Dashed wide E I: Indication of permissible areas of surface treatment,-------- e.g. heat treatment

Table 1 - Types of lines

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continued

Lines Description Application

F Dashed narrow Fl: Hidden outlines-----------------.

F2: Hidden edges

G Long-dashed G I: Centre-lines-.-.-.-.-.---.-- dotted narrow

lineG2: Lines of symmetry

G3: Pitch circle of gears

G4: Pitch circle of holes

H Long-dashed HI: Indication of lines or surfaces to which a special-.-.-.-. dotted wide requirement appliesline H2: Position of cutting planes

J Long-dashed 11: Outlines and edges of adjacent parts-.-_u_---.-_u_--- double-dotted

narrow line12: Alternative and extreme positions of movable parts

13: Centroidallines

J4: Initial outlines prior to forming

J5: Parts situated at the front of the cutting plane

J6: Outlines of alternative executions

17: Outlines of the finished part within blanks

J8: Framing of particular fields/areas

J9: Projected tolerance zone1)This type of line is situated for production of drawings by machines-2)Although two alternatives are available, it is recommended that in anyone drawing, only onetype of line is used.

4.5 Coinciding lines

When two or more lines of different types coincide, the following order of priority should beobserved (see Figure 9):

- visible outlines and edges (continuous wide line, type A);- hidden outlines and edges (dashed line, type E, wide or F, narrow);

- cutting planes (long-dashed dotted wide line, type H);- centre-lines and lines of symmetry (chain narrow line, type G);

- centroidallines (long-dashed double-dotted narrow line, type J);- projection lines (continuous narrow line, type B).

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visible edge over hidden detail

dden detail aver centre line

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Ivisible edge overcentre line

Figure 9 - Priority of coinciding lines

4.6 Leader lines

Leader lines are used to show where dimensions or notes apply. They are type B lines (see Table 1)ending in arrowheads or dots. Leader lines should terminate at the end which touches the features asfollows:

- with a closed and filled or closed arrowhead (included angle 15°) if the leader line ends at lineswhich represent outlines or edges of parts, piping or cables in plans or diagrams; arrowheads arealso drawn at crossing points of these lines with other lines, e.g. lines of symmetry (see Figure 12).

- with a dot (d =5 x line width) if the leader line ends at another line, e.g. dimensionline or line ofsymmetry.

Leader lines are drawn preferably at an angle to the relevant representation and/or the frame limitingthe drawing sheet, and not parallel to adjacent lines, e.g. hatching lines. The inclination to therelevant lines should be greater than 15°, see Figure 10.

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Figure 10 - Dimensioning repeated to avoid long leader lines

An arrowed leader line applied to an arc should be in line with the arc centre. When applied to astraight line an arrowed leader line should be nearly normal to the line. Long or intersecting leaderlines should not be used even if this means repeating dimensions or notes (see Figure 10) or usingletter symbols (see Figure 11).

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~-~'Figure 11 - The use of letter symbols to avoid long and intersecting leader lines

Leader lines should not pass through the intersection of other lines.

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4.7 Arrowheads

Figure 12 - Examples of leader lines

Arrowheads should be triangular, with the length approximately three times the width, formed withstraight lines and symmetrically placed about the dimension line, leader line or stem. Arrowheadsshould be filled in (see Clause 12).

Arrowheads on dimension and leader lines should be 3 mm to 5 mm long. Arrows showing directionof viewing should have arrowheads 7 mm to 10 mm long. The stem of such arrows should beapproximately the same length as the arrowhead, but not less than this.

Relevant standardsBS EN ISO 128:1982BS EN ISO 128-20:1996

BS EN ISO 128-21:1997

BS EN ISO 128-22:1999

BS EN ISO 128-23:1999

BS EN ISO 128-24:1999

BS EN ISO 128-25:1999BS EN ISO 5455: 1995BS EN ISO 6428: 1999

Associated clauseClause 5Clause 7Clause 8Clause 9Clause 10

DescriptionTechnical drawings - General principles of presentationTechnical drawings - General principles of presentation - Part 20:Basic conventions for linesTechnical drawings - General principles of presentation - Part 21:Presentation of lines by CAD systemsTechnical drawings - General principles of presentation - Part 22:Basic conventions and applications for leader lines and reference linesTechnical drawings - Generalprinciplesof presentation- Part 23:Lines of construction drawingsTechnicaldrawings- Generalprinciplesof presentation- Part 24:Lines on mechanical engineering drawingsTechnical drawings - Part 25: Lines on shipbuilding drawingsTechnical drawings - ScalesTechnical drawings - Requirements for microcopying

DescriptionLettering and numeralsSections and sectional viewsSymbols and abbreviationsItem referencesRepresentation of features

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5 Lettering and numerals

5.1 General

The clarity, style, spacing and size of lettering and numerals are important. Numerals should bedrawn clearly as they often have to be read on their own. All strokes should be black and of uniformdensity.

5.2 Style

In general, capital letters should be used. Some suggested examples of letters and numerals areshown below.

.

ABCDEFGH~KLMNOPQRSTUVWXYZ1234567890

ABCDEFGHIJKlMNOPQRSTUVWXYZ

1234567890

5.3 Character height

The dimensions and notes should be not less than 3 mm high. Titles and drawing numbers arenormally larger.

5.4 Direction of lettering

Notes and captions should be placed so that they can be read in the same direction as theinformation in the title block. For dimensions see Clause 12.

5.5 Location of notes

Notes of a general character should be grouped together and not spread over the drawing.

Notes relating to specific details should appear near the relevant features, but not so near as to crowdthe view.

5.6 Underlining

Underlining of notes is not recommended. Larger characters should be used to draw attention to anote or caption.

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6 Views

6.1 General

The presentation of the information should be clear and as complete as necessary. When planningthe layout of a drawing take care with the spacing of the views to make sure that the drawing can beread easily.

6.2 Number of views

Before beginning a drawing it is necessary to have a clear mental picture of the views to be shown.The number of views should be the minimum necessary to ensure that there will be nomisunderstanding. Views should be chosen to need as few hidden lines as possible.

6.3 Partial views

It is not always necessary to draw a full view. Sometimes a partial view is adequate. An example isshown projected from an inclined feature (see view A in Figure 13).

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Figure 13 - Partial view projected from an inclined feature

It may be helpful to draw an enlarged partial view if the general scale of a drawing is so small that aparticular feature cannot be shown clearly or dimensioned adequately. The feature is framed with atype B line (see Table 1) and identified with a capital letter. The feature is then drawn again to astated larger scale with its identification letter (see Figure 14).

DETAIL Z SCALE 5:1

Figure 14 - Enlarged partial view

The boundary which limits a partial view is drawn with a type C or type D line (see Table 1)depending on the length of the boundary (see Figure 14).

24

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7 Sections and sectional views

7.1 General

Sections and sectional views result when cutting planes are passed through an object. Although theterms are often used as if they were interchangeable, they have distinct meanings as follows:

Section: the outlines of the object at the cutting plane only. Visible outlines beyond the cutting planein the direction of viewing are not shown. Therefore, a section has no thickness.

Sectional view: the outline of an object at the cutting plane together with all visible outlines seenbeyond the cutting plane in the direction of viewing.

7.2 Arrangement

The rules for the arrangement of views (see Clause 6 and Clause 7) apply when drawing sectionsand sectional views.

7.3 Cutting planes

The position of the cutting plane(s) should be indicated by means of a long-dashed dotted narrowtype G line (see Table 1). A straight cutting plane should be drawn to a suitable length for legibility(see Figure 20).

If the cutting plane changes its direction, the cutting line should only be drawn at the ends of thecutting plane, where the cutting plane changes direction (see Figures 26 and 27). The cutting linemay be drawn to its full length with a type G line (see Table 1) if necessary for its legibility(see Figure 25).

The direction of viewing is shown by arrows with large heads (see Clause 4), the points of whichtouch the cutting plane. A capital letter, placed close to the stems of the arrows, labels the cuttingplane. The same letter is used in an identifying title, such as A-A, which should be placed below theresulting section or sectional view. If considered necessary the title may be "Section A-A", and thisform is used for both a section and a sectional view (see Figure 20).

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A

~A SECTION A-A

Figure 20 - Indication of cutting planes

Where the position of a single cutting plane is obvious it need not be shown and the resultingsection or sectional view is not given an identifying title. See Clause 11 and Figure 52.

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7.4 Hatching

) In general, sections and sectional views should be hatched but hatching is often omitted in industryto save time and money. It is normal practice to use hatching in British Standards so it has been usedthroughout this publication. Hatching is drawn with type B lines (see Table 1), equally spaced at awell defined angle, preferably at 45°.

Spacing between hatching lines. Hatching lines should not be less than twice the thickness of theheaviest line. It is recommended that these spaces are never be less than 0,7 mm. Considerationshould be given to reproduction since reduction in scale could present a blur (see microcopying andstorage).

Hatching separated areas. Separated sectioned areas of a single component should be hatched in thesame direction and with the same spacing (see Figure 21a».

Hatching assembled parts. Where different sectioned parts meet on an assembly drawing, thedirection of the hatching should normally be reversed and staggered (see Figure 2Ib». In caseswhere hatching on adjacent parts must be at the same angle the lines should be staggered and maybe more closely spaced (see Figure 21c».'"'"")

Hatching large areas. The hatching of a large area may be limited to that part of the area whichtouches adjacent hatched parts or the outline of the large part (see Figure 22).

Thin material in section. Thin material in section may be filled in, in preference to showing thematerial thickness out of scale and hatched. When adjacent parts are thus shown a clear space of notless than 1 mm should be left between them (see Figure 23).

~:~:::~:~:~::] ~~::~:;:~ Ei~~a) Hatching separated areas b) Hatching adjacent parts c) Hatching adjacent parts at

the same angle

Figure 21 - Hatching separated areas and adjacent parts

Figure 22 - Hatching large areas

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Figure 23 - Section through thin material

7.5 Types of sectional views and sections

Sectional views in one plane. Examples of sectional views in one plane are shown in Figure 20 andFigure 24.

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Sectional views in two or more parallel planes. A sectional view in two parallel planes is shown inFigure 25 and one in three parallel, in Figure 26.

Sectional views in intersecting planes. Where a sectional view is taken in two intersecting planes theview, by convention, is drawn as if the two cutting planes were one continuous plane. The part ofthe view on the plane that is not nonnal to the sectional view required is shown moved or revolvedinto the other plane (see Figure 27).

The hatching on sectional views in more than one plane follows the same principle as for sectionalviews in one plane. The thick line portions of the cutting plane show its changes of direction.

AllA

A-A

AT~A

Figure 24 - Sectional view in one plane

A-A

Figure 25 - Sectional view in two parallelplanes where the change of direction of the

cutting plane occurs on a centre-line

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A-AFigure 26 - Sectional view in three parallel planes where the changes in direction of the

cutting plane does not occur on a centre-lineA

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A A-A

A-A

Figure 27 - Sectional views in intersecting planes

Half sectional views. Symmetrical parts may be drawn half in outside view and half in section(see Figure 38).

Local or part sectional views. A local sectional view, shown in Figure 31, may avoid the need for acomplete sectional view. The localized break is shown with a type C line (see Table 1).

Revolved sections. Cross-sections may be revolved in place (see Figure 30). Type B lines(see Table 1) are used for their outlines.

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Removed sections. Cross-sections, instead of being revolved in place, may be removed as shown inFigure 31.

When a removed section is symmetrical it may be shown:

- in projection and is conventionally identified as "section A-A" (see Figure 31);

- in any convenient place on the drawing and is conventionally identified as "section B-B";

- near the main view and connected with it by its line of symmetry through the cutting plane. Theline of symmetry is a type G line (see Table 1). In this case no section identification is needed.

When a removed section is not symmetrical, either the first or second option in the above list shouldbe used.

.

The outline of a removed section is a type A line (see Table 1).

r9~ &-- ~Figure 28 - Half sectional view Figure 29 - Local or part sectional view

Figure 30 - Revolved sections - Example 1

%B-B

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Figure 31 - Removed sections - Example 2 ,)

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Successive sections. Successive removed sections of a part are shown in Figure 32. The sectionsshould all be viewed in the same direction whenever possible. If, through lack of space, successiveremoved sections cannot be shown in true projection, as in Figure 32a), they may be arranged as inFigure 32b).

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Revolved and removed sections, because they have no thickness, are sections and not sectionalviews.

ABC 0--I ---f ---f ---f

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--+I . --+I ---fA --I c 0B

$A-A

a) In projection

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A

A-A

c

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b) Alternative arrangement

Figure 32 - Successive sections

7.6 Parts and features of parts not normally sectioned

33

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When a sectional view is given where the cutting plane passes longitudinally through fasteners, suchas bolts, nuts, shafts, ribs, webs, spokes of wheels, etc., it is the practice to show them in externalview (see Figure 33).

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B

~A

A-A

B-B

Figure 33 - Cutting plane passing longitudinally through fasteners

Relevant standardsBS ISO 128:1982BS ISO 128-40:2001

BS ISO 128-50:2001

BS EN ISO 7519:1997

Associated clausesClause 1Clause 2Clause 4Clause 5Clause 8Clause 9Clause 10Clause 12Clause 14Clause 15

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DescriptionTechnicaldrawings - Generalprinciplesof presentationTechnical drawings - General principles of presentation -Part 40: Basic conventions for cuts and sectionsGeneral principles of presentation - Part 50: Basic conventions forrepresenting areas on cuts and sectionsTechnicaldrawings - Constructiondrawings- General principles ofpresentation for general arrangement and assembly drawings

DescriptionLayout of drawingsScalesLines and arrowsLettering and numeralsSymbols and abbreviationsItem referencesRepresentation of featuresDimensioningTolerancingMethod of indicating surface texture

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34

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8 Symbols and abbreviations

8.1 General

Symbols and abbreviations are used on drawings to save space and time whilst giving precise andclear descriptions. Only those symbols and abbreviations that are commonly used and understoodshould be used. A selection is given in 8.3. Others symbol and abbreviations should be avoided andthe intended meaning expressed in words. Abbreviations are the same in the singular and plural. Fullstops are only used where the abbreviation itself makes a word (e.g. NO. and FIG).

8.2 Welding symbols

Where welds are to be shown by means of symbols, reference should be made toBS ISO 2553:1992.

8.3 Commonly accepted symbols and abbreviations

Term Abbreviation

Acrossflats AFAssembly ASSYCentres CRSCenn:e line: ta vIew. . . . . . . . . . . . . . . . . . . . .

in a note CLChamfered, chamfer (in a note) ... CHAMCheesehead CHHDCountersunk CSKCountersunk head. . . . . . . . . . . . . CSK HDCounterbore CBORECylinder or cylindrical. . . . . . . . . . CYLDiameter (in a note) . . . . . . . . . . . . DIADiameter (preceding a dimension) .0Drawing DRGEqually spaced EQUISPExternal EXTFigure FIGHexagon HEXHexagonhead HEXHDHydraulic HYDInsulated or insulation. . . . . . . . . . INSULInternal INTLefthand LHLong LGMaterial MATLMaximum MAXMinimum MINNumber NO.

Term Abbreviation

Pattern number PATINO.Pitch circle diameter. . . . . . . . . . . PCDRadius (in anote) RADRadius (preceding a dimension) . . . RRequired REQDRighthand RHRoundhead RDHDScrew (or screwed) SCRSheet SHSketch SKSpecification SPECSpherical diameter(only preceding a dimension) . . . . . S 0Spherical radius(only preceding a dimension) . . . . . SRSpotface SFACESquare(inanote) SQSquare (preceding a dimension) .. .Standard STDTaper, on a diameter or width(Orientated to direction of taper) .. C>Thread THDTypical or typically. . . . . . . . . . . . TYPUndercut UCUTVolume VOLWeight WT

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- Relevant standardsBS EN 22553:1995

BS 5575-0:1993

Associated clausesClause 4Clause 5Clause 9

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DescriptionWelded, brazed and soldered joints - Symbolic representation ondrawingsSpecification for qualities, units and symbols - Part 0: Generalprinciples

DescriptionLines and arrowsLettering and numeralsItem references

)

36

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9 Item references

9.1 General

Item references are used on assembly drawings to identify the items in the assembly. Item referencesare shown in an item list that gives information such as the multiple required of each item and itspart number. The item list may appear on the assembly drawing (see Figure 3d)) or separately.

Numerals are generally used for item references (see Figure 34). The numerals should be at leasttwice the height of characters used for dimensions and notes and are generally encircled with atype B line (see Table 1).

9.2 Arrangement

Item references should preferably be arranged in columns and rows. They should be connected tothe items by leader lines ending in dots within the item outlines. When this is not possible,arrowheads may be used touching the outlines. The leader lines should not be drawn at right anglesto the outlines of the items to which they refer.

9.3 Similar items used more than once

Similar items used more than once generally need only one item reference. The number used isgiven by a small numeral placed to the right and slightly below the item reference (see Figure 34,items 6 to 8).

9.4 Associated items

Only one leader should be used for item references of associated items (see Figure 34, items 6 to 8and 9 to 12). The circles should either touch or be joined with a short type B line (see Table 1).

9.5 Assembly instructions

Any necessary assembly instructions can be added to an item reference (see Figure 34, item 4).

Figure 34 - Item references

37

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$10.8 Screw threads

Figure 46 - Serrations

For all normal purposes the conventional representation of screw threads, as shown in Figure 47 andFigure 48, is preferred whatever the screw thread type.

Thread run-outs. These are only shown where they are functionally necessary. The method ofindication is shown on the stud Figure 48a).

Assembled threaded parts. Externally threaded parts are shown covering internally threaded parts onsectional views and end views (see Figure 48a) and Figure 48b».

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Figure 47 - Conventions for screw threads42

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a) b)

Figure 48 - Conventions for assembled screw threads

EtdevantstandardsBS EN ISO 6410-1:1996

BS EN ISO 6410-2:1996

BS EN ISO 6410-3:1996

BS EN ISO 6413:1995BS EN ISO 9222-1: 1995

BS EN ISO 9222-2: 1995

Associated clausesClause 4Clause 5Clause 6Clause 8Clause 12

DescriptionTechnical drawings - Screw threads and threaded parts -Part 1: General conventionsTechnical drawings - Screw threads and threaded parts -Part 2: Screw thread insertsTechnical drawings - Screw threads and threaded parts -Part 3: Simplified representationTechnical drawings - Representation of splines and serrationsTechnical drawings - Seals for dynamic application -Part 1: General simplified representationsTechnical drawings - Seals for dynamicrepresentation-Part 2: Detailed simplified representation

DescriptionLines and arrowsLettering and numeralsViewsSymbols and abbreviationsDimensioning

43

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12 Dimensioning

12.1 General

This clause establishes the general principles of dimensioning applicable in all fields(i.e. mechanical, electrical and civil engineering, architecture, etc.). It is possible that in somespecific technical areas that general rules and conventions will not cover all the needs of specializedpractices adequately. In such cases additional rules may be laid down in standards specific to theseareas.

12.2 Types of dimension

For the purposes of this clause, the following definitions apply.

Dimension: numerical value expressed in appropriate units of measurement and indicatedgraphically on technical drawings with lines, symbols and notes.

Dimensions are classified according to the following types:

Functional dimension: dimension that is essential to the function of the piece or space ("P' inFigure 55).

Non-functional dimension: dimension that is not essential to the function of the piece or space("NP' Figure 55).

Auxiliary dimension: dimension given for information purposes only. It does not govern productionor inspection operations and is derived from other values shown on the drawing or in relateddocuments. An auxiliary dimension is given in parentheses and no tolerance may be applied to it("AUX" in Figure 55).

Feature: individual characteristic such as a flat surface, a cylindrical surface, two parallel surfaces, ashoulder, a screw thread, a slot, a profile, etc.

End product: complete part ready for assembly or service, or a configuration produced from adrawing specification. An end product may also be a part ready for further processing (for example,a product from a foundry or forge) or a configuration needing further processing.

F FNF

F

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AUX) NF

a) Design requirement b) Shoulder screw c) Threaded hole

Figure 55 - Functional and non-functional dimensions

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12.3 Application

All dimensional infonnation necessary to define a part or component clearly and completely shouldbe shown directly on a drawing unless this information is specified in associated documentation.Each feature should be dimensioned once only in a drawing. Dimensions should be placed on theview or section that most clearly shows the corresponding features.

Each drawing should use the same unit (e.g. millimetres) for all dimensions but without showing theunit symbol. In order to avoid misinterpretation, the predominant unit symbol on a drawing may bespecified in a note. Where other units have to be shown as part of the drawing specification(e.g. N.m for torque or kPa for pressure), the appropriate unit symbol should be shown with thevalue.

No more dimensions than are necessary to define a part or an end product should be shown on adrawing. No feature of a part of an end product should be defined by more than one dimension inanyone direction. Exception may, however, be made:

- where it is necessary to give additional dimensions at intermediate stages of production (e.g. thesize of a feature prior to carburizing and finishing);

- where the addition of an auxiliary dimension would be advantageous.

Production process inspection methods should not be specified unless they are essential to ensuresatisfactory function or interchangeability.

Functional dimensions should be shown directly on the drawing wherever possible (see Figure 56).

Figure 56 - Functional dimensioning

Occasionally indirect functional dimensioning is justified or necessary. In such cases, care should beexercised so that the effect of directly shown functional dimensioning is maintained. Figure 57shows the effect of acceptable indirect functional dimensioning that maintains the dimensionalrequirements established by Figure 56.

Figure 57 - Indirect functional dimensioning )

50

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12.4 Method of dimensioning

The elements of dimensioning include the projection line, dimension line, leader line, dimension linetermination, the origin indication and the dimension itself. The various elements of dimensioning areillustrated in Figure 58 and Figure 59 (see BS ISO 128).

Projection line

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V Value of t~ dimension

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Dimension line

Figure 58 - Projection lines and dimension lines - Example 1

Projection line

4240.,.Value of the dlmensio

Termination (Oblique stroke.Dimension line"-

Figure 59 - Projection lines and dimension lines - Example 2

12.5 Projection lines, dimension lines and leader lines

Projection lines and dimension lines are drawn as narrow continuous lines as shown in BS ISO 128and as illustrated in Figure 58 and Figure 59.

Projection lines should extend slightly beyond the respective dimension lines (see Figure 58 andFigure 59).

Projection lines should be drawn perpendicular to the feature being dimensioned. Where necessary,however, they may be drawn obliquely, but parallel to each other (see Figure 60).

Intersecting construction and projection lines should extend approximately eight times the line widthbeyond their point of intersection (see Figure 61.)

In general, projection lines and dimension lines should not cross unless it is unavoidable (Figure 62).

A dimension line should be shown unbroken where the feature to which it refers is shown broken(see Figure 63).

Intersecting projection lines and dimension lines should be avoided. Where unavoidable, however,neither line should be shown with a break (see Figure 62 and Figure 64).

A centre-line or the outline of a part should not be used as a dimension line but may be used in placeof projection line (see Figure 64).

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Figure 60 - Dimension lines drawnobliquely, but parallel

Figure 61 - Intersecting construction andprojection lines

Figure 62 - Unavoidable intersection ofdimension and projection lines

Figure 63 - Dimensioning a broken feature

Figure 64 - Centre-line and/or outline of a part used in place of a projection line

12.6 Terminations and origin indication

Dimension lines should have distinct terminations (Le. either arrowheads or oblique strokes), or,where applicable, an origin indication.

Two dimensional line terminations (see Figure 65) and an origin indication (see Figure 66) areshown in this clause. They are:

a) The arrowhead, drawn as short lines forming barbs at any convenient included angle between15° and 90°. The arrowhead may be open, closed or closed and filled in (see Figure 65a».

b) The oblique stroke, drawn as a short line inclined at 45° (see Figure 65b».

c) The origin indication, drawn as a small open circle approximately 3 mm in diameter.

The size of the terminations should be proportionate to the size of drawing on which they are usedbut not larger than is necessary to read the drawing.

52

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13.6 Chamfers and countersinks

Chamfers should be dimensioned as shown in Figure 103. Where the chamfer angle is 45°, theindications may be simplified as shown in Figures 104 and 105.

or 313

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2x45°

Figure 104 - 45° chamfers simplified

or

2x45°

2x 45°

Figure 105 - Dimensioning internal chamfers

Countersinks are dimensioned by showing either the required diametral dimension at the includedangle, or the depth and the included angle (see Figure 106).

or

5

Figure 106 - Dimensioning countersinks

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