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Engineering Part 2: A guide for higher education to as 8888:2000, Technical product documentation
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Contents Contents Foreword Scope Listoffigures,tablesanddrawings... 1 Layout of drawings 2Scales 3Projection 4Linesandarrows 5Letteringandnumerals 6Views 7 Sections and sectional views 8Symbolsandabbreviations 9Itemreferences 10 Representation of features 11 Representation of components 12Dimensioning 13Dimensioningfromacommonfeature
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..4 9 13 14 17 22 24 28 35 37 39 44 49 58
14 Tolerancing
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15Methodsofindicatingsurfacetexture.., 16Diagrams 17 Microcopying and storage Annex A (informative) Correspondence between BS 308-1 and BS 8888. . . . . . . . . . . . . . . . Annex B (informative) Examples of mechanical engineering drawings. . . . . . . . . . . . . . . . . Annex C (informative) Approaches to 3-D modelling.
71 101 109 112 116 119
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Annex D (informative) A model of geometric product specification (GPS) and verification. . 122 AnnexE(informative)BS8888kits 128 Annex F (informative) Examples of the application of different types of line. . . . . . . . . . . . 130 Bibliography 139 Index 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, including those produced by computers. 1.2 Drawing sheets The "A" series of drawing sheets, shown in Figure 1, is normally used. The drawing area and title block should be within a frame border. In general, material within the frame border forms part of any contract requirements.
= 210 mm = 297 rom = 420 mm
x 297 mm x 420 mm x 594 mm = 594 rom x 841 rom AO = 841 mm x 1189 rom The sides of all sheets are in the ratio 1: ff A4
A3 A2 Al
AO is normally one square metre in area and forms the basis of 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 to the lower right-hand comer of the frame. Only sheets positioned horizontally are permitted for these formats. 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 the drawings 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 should be provided with all sizes. The border should be 20 mm wide on the left edge, including the width of the frame. It can be used as a filing margin. All other borders are 10 mm wide (See Figure 2). 2
4
Dimensions in millimetres
5
3
20
Key 1 Trimming mark 2 Trimmed format 3 Grid reference
4 Frame of drawing space 5 Drawing space 6 Untrimmed format Figure 2
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Borders
1.5 Drawing formats Drawing sheets may be produced in two formats. Portrait format is intended to be viewed with the longest side of the sheet vertical, see Figure 3a). Landscape format is intended to be viewed with the longest 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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d) Assembly drawing Types of drawings
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1.6 Types of drawings There are different types of drawings, two of which, detail and assembly type drawings, are shown in 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 8888 should 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 appropriate requirements of all relevant cross-referenced standards, in addition to the requirements directly stated in BS 8888, have been met.
If the TPD has been prepared using the independency system of tolerancing, the symbol identifying the number of the standard should be supplemented by the letter "I" contained within an equilateral triangle, as shown in Figure 4.
8S 8888 Figure 4
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Method of indicating that the independency system of tolerancing has been used
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Relevant standards BS EN ISO 5457:1999 BS EN ISO 3098-0: 1998
BS EN ISO 5455:1994 BS ISO 7200: 1984 BS ISO 9958-1: 1992 BS 8888:2000
Associated clauses Clause 2 Clause 3 Clause 4 Clause 9
Description Technical product documentation - Sizes and layout of drawing sheets Technical product documentation - Lettering - Part 0: General requirements Technical drawings - Scales Technical drawings - Title blocks Draughting media for technical drawings - Draughting film with polyester base - Part I: Requirements and marking Technical product documentation (TPD) - Specification for defining, specifying and graphically representing products Description Scales Projection Lines and arrows Item references
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2 Scales )
2.1 General
Every drawing should be drawn in proportion, i.e. to a uniform scale. The scale used should be stated 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:
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For drawings represented full size: 1:1
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On drawings smaller than full size (reduction scales): 1:2
1:5
1:10
1:20
1:50
1:100
1:200 1:500 1:1000
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On drawings larger than full size (enlargement scales): 2:1
5:1
20:1
50:1
10:1
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 the object to be depicted. The scale should be large enough to permit easy and clear interpretation of the information. Details that are too small for clear dimensioning in the main representation should be shown in a separate view to a larger scale, see Figure 14.
Relevant standards BS EN ISO 5455:1995
Description Technical drawings
Associated clauses Clause 1 Clause 4 Clause 5 Clause 12 Clause 13
Description Layout of drawing Lines and arrows Letterings and numerals Dimensioning Dimensioning from a common feature
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Scales
3 Projection 3.1 General In this section only orthographic representations will be defined. Orthographic representations are obtained by means of parallel orthogonal projections. They result in flat, two-dimensional views systematically 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 viewing should be clearly shown. An arrow and view title may be used, similar to those in Figure 14. The most informative view of the object to be represented is normally chosen as the principal view (front view). The principal view usually shows the object in the functioning or manufacturing mounting position. 3.2 Projection symbols The system of projection used on a drawing should be indicated by the appropriate symbol given in Figure 5. Projection
Symbol
Firstangle
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Third angle
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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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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 to show all six views.
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Example of first angle projection
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Relevant standards BS EN ISO 5456-1:1999 BS 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 clauses Clause 5 Clause 6
Description Technical drawings - Projection methods - Part 1: Synopsis Technical drawings - Projection methods - Part 2: Orthographical representation Technical drawings - Projection methods - Part 3: Axonometric representations Technical product documentation - Vocabulary - Part 2: Terms relating to projection methods Technical 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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Description Lettering and numerals Views
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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 without interruptions. 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 drawings see 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 the
type 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 be constant along the whole line. The minimum spacing between parallel lines should not be less than 0,7 rom, unless rules to the contrary are stated in other International Standards. NOTE In certain cases when computer-aided drawing techniques are used, the spacing of lines on the drawing does not represent the actual spacing, e.g. for the representation of screw threads. This fact has to be considered when data sets are established, e.g. for the operation 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 the proportion shown in Table 1. Dashed lines should start and end with dashes in contact with the hidden or visible lines from which they originate, except when the hidden line continues a visible line. 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 the length 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 the line.
Centre-lines should extend only a short distance beyond the feature or view to which they apply. If required for dimensioning they should continue as projection lines. Common centre-lines should not extend across the space between adjacent views. Centre-lines should not stop at another line of the drawing. Where angles are formed in chain lines, long dashes should meet or cross at comers.
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Table 1 - Types of lines Line
Description
A
Continuous wide
B
Continuous narrow
Continuous ~narrow irregularZ)
C
~Continuous narrow straight with zigzagsl),Z) E
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Dashed wide
Application AI: Visible outlines 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 BI: Imaginary lines of intersection 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 B 13: Indication ofrepetitive details B14: Interpretation lines oftapered features B15: Location of laminations B16: Extension lines B 17: Grid lines C 1: Preferably manually represented termination of partial or interrupted views, cuts and sections, if the limit is not a line of symmetry or a centre line, (see Figure 107 and Figure 108) D 1: Mechanically represented termination of partial or interrupted views, cuts and sections, if the limit is not a line of symmetry or a centreline, (see Figure 101 and Figure 118) E I: Indication of permissible areas of surface treatment, e.g. heat treatment
continued
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Lines F
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Description Dashed narrow
Application Fl: Hidden outlines F2: Hidden edges
Long-dashed dotted narrow line
G I: Centre-lines G2: Lines of symmetry G3: Pitch circle of gears G4: Pitch circle of holes
H -.-.-.-. J -.-_u_---.-_u_---
Long-dashed dotted wide line Long-dashed double-dotted narrow line
HI: Indication of lines or surfaces to which a special requirement applies H2: Position of cutting planes 11: Outlines and edges of adjacent parts 12: 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 zone
1)This type of line is situated for production of drawings by machines2) Although two alternatives are available, it is recommended that in anyone drawing, only one type of line is used.
4.5 Coinciding lines When two or more lines of different types coincide, the following order of priority should be observed (see Figure 9):
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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
hidden
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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 as follows:
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with a closed and filled or closed arrowhead (included angle 15°) if the leader line ends at lines which represent outlines or edges of parts, piping or cables in plans or diagrams; arrowheads are also drawn at crossing points of these lines with other lines, e.g. lines of symmetry (see Figure 12).
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with a dot (d = 5 x line width) if the leader line ends at another line, e.g. dimension line or line of symmetry.
Leader lines are drawn preferably at an angle to the relevant representation and/or the frame limiting the drawing sheet, and not parallel to adjacent lines, e.g. hatching lines. The inclination to the relevant 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 a straight line an arrowed leader line should be nearly normal to the line. Long or intersecting leader lines should not be used even if this means repeating dimensions or notes (see Figure 10) or using letter symbols (see Figure 11).
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Figure 12 - Examples of leader lines 'i
4.7 Arrowheads Arrowheads should be triangular, with the length approximately three times the width, formed with straight lines and symmetrically placed about the dimension line, leader line or stem. Arrowheads should be filled in (see Clause 12). Arrowheads on dimension and leader lines should be 3 mm to 5 mm long. Arrows showing direction of viewing should have arrowheads 7 mm to 10 mm long. The stem of such arrows should be approximately the same length as the arrowhead, but not less than this. Relevant standards BS EN ISO 128:1982 BS 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 128-25:1999 BS EN ISO 5455: 1995 BS EN ISO 6428: 1999 Associated clause Clause 5 Clause 7 Clause 8 Clause 9 Clause 10
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Description Technical drawings - General principles of presentation Technical drawings - General principles of presentation - Part 20: Basic conventions for lines Technical drawings - General principles of presentation - Part 21: Presentation 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 - Generalprinciples of presentation - Part 23: Lines of construction drawings Technicaldrawings- Generalprinciples of presentation - Part 24: Lines on mechanical engineering drawings Technical drawings - Part 25: Lines on shipbuilding drawings Technical drawings - Scales Technical drawings - Requirements for microcopying Description Lettering and numerals Sections and sectional views Symbols and abbreviations Item references Representation of features 21
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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 be drawn clearly as they often have to be read on their own. All strokes should be black and of uniform density.
5.2 Style In general, capital letters should be used. Some suggested examples of letters and numerals are .
shown below.
ABCDEFGH~KLMNOPQRSTUVWXYZ 1234567890 ABCDEFGHIJKlMNOPQRSTUVWXYZ
1234567890
5.3 Character height The dimensions and notes should be not less than 3 mm high. Titles and drawing numbers are normally larger. 5.4 Direction of lettering Notes and captions should be placed so that they can be read in the same direction as the information 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 crowd the view. 5.6 Underlining Underlining of notes is not recommended. note or caption.
Larger characters should be used to draw attention to a
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6 Views 6.1 General The presentation of the information should be clear and as complete as necessary. When planning the layout of a drawing take care with the spacing of the views to make sure that the drawing can be read 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 no misunderstanding. 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 is shown projected from an inclined feature (see view A in Figure 13).
" Figure 13
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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 a particular feature cannot be shown clearly or dimensioned adequately. The feature is framed with a type B line (see Table 1) and identified with a capital letter. The feature is then drawn again to a stated larger scale with its identification letter (see Figure 14).
DETAIL Z SCALE 5:1
Figure 14
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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 the terms 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 plane in 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 seen beyond 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 sections and sectional views. 7.3 Cutting planes The position of the cutting plane(s) should be indicated by means of a long-dashed dotted narrow type 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 the cutting plane, where the cutting plane changes direction (see Figures 26 and 27). The cutting line may 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 which touch the cutting plane. A capital letter, placed close to the stems of the arrows, labels the cutting plane. The same letter is used in an identifying title, such as A-A, which should be placed below the resulting section or sectional view. If considered necessary the title may be "Section A-A", and this form is used for both a section and a sectional view (see Figure 20).
(t>EJ A
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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 resulting section 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 industry to save time and money. It is normal practice to use hatching in British Standards so it has been used throughout this publication. Hatching is drawn with type B lines (see Table 1), equally spaced at a well defined angle, preferably at 45°. Spacing between hatching lines. Hatching lines should not be less than twice the thickness of the heaviest line. It is recommended that these spaces are never be less than 0,7 mm. Consideration should be given to reproduction since reduction in scale could present a blur (see microcopying and storage). Hatching separated areas. Separated sectioned areas of a single component should be hatched in the same direction and with the same spacing (see Figure 21a».
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Hatching assembled parts. Where different sectioned parts meet on an assembly drawing, the direction of the hatching should normally be reversed and staggered (see Figure 2Ib». In cases where hatching on adjacent parts must be at the same angle the lines should be staggered and may be more closely spaced (see Figure 21c». Hatching large areas. The hatching of a large area may be limited to that part of the area which touches 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 the material thickness out of scale and hatched. When adjacent parts are thus shown a clear space of not less than 1 mm should be left between them (see Figure 23).
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a) Hatching separated areas
b) Hatching adjacent parts
Figure 21
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Hatching separated areas and adjacent parts
Figure 22
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Hatching large areas
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Figure 23
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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 and Figure 24.
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Sectional views in two or more parallel planes. A sectional view in two parallel planes is shown in Figure 25 and one in three parallel, in Figure 26. Sectional views in intersecting planes. Where a sectional view is taken in two intersecting planes the view, by convention, is drawn as if the two cutting planes were one continuous plane. The part of the view on the plane that is not nonnal to the sectional view required is shown moved or revolved into the other plane (see Figure 27). The hatching on sectional views in more than one plane follows the same principle as for sectional views in one plane. The thick line portions of the cutting plane show its changes of direction.
lA Al
A-A
AT~A Figure 24
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A-A Figure 25 - Sectional view in two parallel planes where the change of direction of the cutting plane occurs on a centre-line
Sectional view in one plane
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A-A Figure 26 - Sectional view in three parallel planes where the changes in direction of the cutting plane does not occur on a centre-line
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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 a complete 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. 31
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Removed sections. Cross-sections, instead of being revolved in place, may be removed as shown in Figure 31. When a removed section is symmetrical it may be shown:
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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. The line 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 should .
be used.
The outline of a removed section is a type A line (see Table 1).
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Figure 29 - Local or part sectional view
Half sectional view
Figure 30 - Revolved sections
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Figure 31 - Removed sections
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Successive sections. Successive removed sections of a part are shown in Figure 32. The sections should all be viewed in the same direction whenever possible. If, through lack of space, successive removed sections cannot be shown in true projection, as in Figure 32a), they may be arranged as in Figure 32b). Revolved and removed sections, because they have no thickness, are sections and not sectional views.
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Figure 32 - Successive sections 7.6 Parts and features of parts not normally sectioned When a sectional view is given where the cutting plane passes longitudinally through fasteners, such as bolts, nuts, shafts, ribs, webs, spokes of wheels, etc., it is the practice to show them in external view (see Figure 33).
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Figure 33 Relevant standards BS ISO 128:1982 BS ISO 128-40:2001 BS ISO 128-50:2001 BS EN ISO 7519:1997
Associated clauses Clause 1 Clause 2 Clause 4 Clause 5 Clause 8 Clause 9 Clause 10 Clause 12 Clause 14 Clause 15
A-A A
B-B Cutting plane passing longitudinally through fasteners Description
Technicaldrawings - Generalprinciplesof presentation Technical drawings - General principles of presentation Part 40: Basic conventions for cuts and sections General principles of presentation - Part 50: Basic conventions for representing areas on cuts and sections Technicaldrawings - Constructiondrawings - General principles of presentation for general arrangement and assembly drawings Description Layout of drawings Scales Lines and arrows Lettering and numerals Symbols and abbreviations Item references Representation of features Dimensioning Tolerancing Method of indicating surface texture
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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 and clear descriptions. Only those symbols and abbreviations that are commonly used and understood should be used. A selection is given in 8.3. Others symbol and abbreviations should be avoided and the intended meaning expressed in words. Abbreviations are the same in the singular and plural. Full stops 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 to BS ISO 2553:1992. 8.3 Commonly accepted symbols and abbreviations Term
Abbreviation
Term
Acrossflats AF Assembly ASSY Centres CRS Cenn:e line: a vIew. . . . . . . . . . . . . . . . . . . . . in a note CL Chamfered, chamfer (in a note) ... CHAM Cheesehead CHHD Countersunk CSK Countersunk head. . . . . . . . . . . . . CSK HD Counterbore CBORE Cylinder or cylindrical. . . . . . . . . . CYL
Abbreviation
Pattern number PATINO. Pitch circle diameter. . . . . . . . . . . PCD Radius (in anote) RAD Radius (preceding a dimension) . . . R Required REQD Righthand RH Roundhead RDHD Screw (or screwed) SCR Sheet SH Sketch SK Specification SPEC Spherical diameter (only preceding a dimension) . . . . . S 0 Spherical radius (only preceding a dimension) . . . . . SR Spotface SFACE Square(inanote) SQ Square (preceding a dimension) .. . Standard STD Taper, on a diameter or width (Orientated to direction of taper) .. C> Thread THD Typical or typically. . . . . . . . . . . . TYP Undercut UCUT Volume VOL Weight WT
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Diameter (in a note) . . . . . . . . . . . . DIA Diameter (preceding a dimension) .0 Drawing DRG Equally spaced EQUISP External EXT Figure FIG Hexagon HEX Hexagonhead HEXHD Hydraulic HYD Insulated or insulation. . . . . . . . . . INSUL Internal INT Lefthand LH Long LG Material MATL Maximum MAX Minimum MIN Number NO.
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- Relevant standards BS EN 22553:1995
BS 5575-0:1993
Associated clauses Clause 4 Clause 5 Clause 9
Description Welded, brazed and soldered joints - Symbolic representation on drawings Specification for qualities, units and symbols - Part 0: General principles Description Lines and arrows Lettering and numerals Item references
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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 references are shown in an item list that gives information such as the multiple required of each item and its part 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 least twice the height of characters used for dimensions and notes and are generally encircled with a type B line (see Table 1).
9.2 Arrangement Item references should preferably be arranged in columns and rows. They should be connected to the 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 angles to 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 is given 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 8 and 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 111111--
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$ Figure 46 - Serrations 10.8 Screw threads For all normal purposes the conventional representation of screw threads, as shown in Figure 47 and Figure 48, is preferred whatever the screw thread type. Thread run-outs. These are only shown where they are functionally necessary. The method of indication is shown on the stud Figure 48a). Assembled threaded parts. Externally threaded parts are shown covering internally threaded parts on sectional views and end views (see Figure 48a) and Figure 48b».
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Conventions for screw threads 42
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Etdevantstandards BS EN ISO 6410-1:1996 BS EN ISO 6410-2:1996 BS EN ISO 6410-3:1996 BS EN ISO 6413:1995 BS EN ISO 9222-1: 1995 BS EN ISO 9222-2: 1995
Associated clauses Clause 4 Clause 5 Clause 6 Clause 8 Clause 12
b)
-
Conventions for assembled screw threads
Description Technical drawings - Screw threads and threaded parts Part 1: General conventions Technical drawings - Screw threads and threaded parts Part 2: Screw thread inserts Technical drawings - Screw threads and threaded parts Part 3: Simplified representation Technical drawings - Representation of splines and serrations Technical drawings - Seals for dynamic application Part 1: General simplified representations Technical drawings - Seals for dynamicrepresentation Part 2: Detailed simplified representation Description Lines and arrows Lettering and numerals Views Symbols and abbreviations Dimensioning
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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 some specific technical areas that general rules and conventions will not cover all the needs of specialized practices adequately. In such cases additional rules may be laid down in standards specific to these areas. 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 indicated graphically 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' in Figure 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 production or inspection operations and is derived from other values shown on the drawing or in related documents. 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, a shoulder, a screw thread, a slot, a profile, etc. End product: complete part ready for assembly or service, or a configuration produced from a drawing 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
F
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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 should be 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 the view 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 the unit symbol. In order to avoid misinterpretation, the predominant unit symbol on a drawing may be specified 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 the value. No more dimensions than are necessary to define a part or an end product should be shown on a drawing. No feature of a part of an end product should be defined by more than one dimension in anyone direction. Exception may, however, be made:
-
where it is necessary to give additional dimensions at intermediate stages of production (e.g. the size 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 ensure satisfactory function or interchangeability. Functional dimensions should be shown directly on the drawing wherever possible (see Figure 56).
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Figure 56 - Functional dimensioning Occasionally indirect functional dimensioning is justified or necessary. In such cases, care should be exercised so that the effect of directly shown functional dimensioning is maintained. Figure 57 shows the effect of acceptable indirect functional dimensioning that maintains the dimensional requirements established by Figure 56.
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12.4 Method of dimensioning The elements of dimensioning include the projection line, dimension line, leader line, dimension line termination, the origin indication and the dimension itself. The various elements of dimensioning are illustrated in Figure 58 and Figure 59 (see BS ISO 128).
Projection line
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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 128 and as illustrated in Figure 58 and Figure 59. Projection lines should extend slightly beyond the respective dimension lines (see Figure 58 and Figure 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 width beyond 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 place of projection line (see Figure 64).
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Figure 60 - Dimension lines drawn obliquely, but parallel
Figure 61 - Intersecting construction and projection lines
Figure 62 - Unavoidable intersection of dimension and projection lines
Figure 63 - Dimensioning a broken feature
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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) are shown in this clause. They are: a) The arrowhead, drawn as short lines forming barbs at any convenient included angle between 15° 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 used but not larger than is necessary to read the drawing.
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13.6 Chamfers and countersinks Chamfers should be dimensioned as shown in Figure 103. Where the chamfer angle is 45°, the indications may be simplified as shown in Figures 104 and 105.
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2 Figure 103 - Chamfers dimensioned 2x45°
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Figure 105 - Dimensioning internal chamfers Countersinks are dimensioned by showing either the required diametral dimension at the included angle, or the depth and the included angle (see Figure 106).
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29.09.01
CHECKED BY: G.E. TORRENS DATE: 08.10.01
DATE:
DRAWN BY: G.LWlWAMS
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GENERAL TOLERANCES:
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DIMENSIONS
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DETAIl.. X SCALE 6: 1
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DO NOT SCALE IN ACCORDANCE WITHBS 8888 ANISH: MA1ERIAL: / STEEL TO 8 S 970 'V ALL OVER REVISION: 02.11.01 PR..ECTlON: FIRST ANGLE ORIGINAL SCALE: 1: 1
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