The Essential Guide to
Technical Product Specification:
Engineering Drawing
Colin Simmons
and
Neil Phelps
First published in the UK in 2009 by
BSI
389 Chiswick High Road
London W4 4AL
© British Standards Institution 2009
All rights reserved. Except as permitted under the Copyright, Designs and Patents Act 1988, no part of this publication
may be reproduced, stored in a retrieval system or transmitted in any form or by any means – electronic, photocopying,
recording or otherwise – without prior permission in writing from the publisher.
Whilst every care has been taken in developing and compiling this publication, BSI accepts no liability for any loss or
damage caused, arising directly or indirectly in connection with reliance on its contents except to the extent that such
liability may not be excluded in law.
While every effort has been made to trace all copyright holders, anyone claiming copyright should get in touch with the
BSI at the above address.
BSI has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in
this book, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.
The right of Colin Simmons and Neil Phelps to be identified as the authors of this Work has been asserted by them in
accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988.
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Printed in Great Britain by Berforts Group, Stevenage
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 978 0 580 62673 9
v
Contents
Introduction
Dimensioning and tolerancing of size
1.1 Introduction
1.2 General principles
1.3 Types of dimension
1.4 Dimensioning conventions
1.5 Arrangement of dimensions
1.6 Methods for dimensioning common features
1.7 Dimensioning screw threads and threaded parts
1.8 Dimensioning chamfers and countersinks
1.9 Equally spaced repeated features
1.10 Dimensioning of curved profiles
1.11 Dimensioning of keyways
1.12 Tolerancing
1.13 Interpretations of limits of size for a feature-of-size
1.14 Datum surfaces and functional requirements
1.15 Relevant standards
Geometric tolerancing datums and datum systems
2.1 Introduction
2.2 Terms and definitions
2.3 Basic concepts
2.4 Symbols
2.5 Tolerance frame
2.6 Toleranced features
2.7 Tolerance zones
2.8 Datums and datum systems
2.9 Supplementary indications
2.10 Examples of geometrical tolerancing
2.11 Relevant standards
Graphical symbols for the indication of surface texture
3.1 Introduction
3.2 The basic graphical symbol
3.3 Expanded graphical symbols
3.4 Mandatory positions for the indication of surface texture requirements
3.5 Surface texture parameters
3.6 Indication of special surface texture characteristics
3.7 Indications on drawings
3.8 Relevant standards
vii
1
1
1
2
3
4
9
12
13
14
16
17
18
19
21
21
23
23
23
26
27
29
29
32
37
45
64
114
115
115
115
115
116
117
118
120
123
vi
The Essential Guide to Technical Product Specification: Engineering Drawing
Welding, brazed and soldered joints – Symbolic representation
4.1 Introduction
4.2 Relevant standards
Limits and fits
5.1 Introduction
5.2 Selected ISO fits – Hole basis
5.3 Selected ISO fits – Shaft basis
5.4 Methods of specifying required fits
5.5 Relevant standards
Metric screw threads
6.1 Introduction
6.2 Thread designation
6.3 Relevant standards
Illustrated index to BS 8888
Normative references
125
125
133
135
135
135
138
140
140
141
141
141
168
169
169
vii
Introduction
This guide has been produced as a companion to BS 8888, presenting up-to-date information based on
the technical product specification aspects of BS 8888 and the essential standards it references.
Its aim is to offer straightforward guidance together with pictorial representations, to all practitioners
of technical product specification, i.e. those currently using BS 8888 and those who, in a bid to conform
to global ISO practices, are making or wish to make, the transition from the old BS 308 to BS 8888.
Its scope is to provide the necessary tools to enable engineers engaged in design specification,
manufacturing and verification with the essential basic information required for specifying a product or
component.
It includes comprehensive sections extracted from and referenced to international standards relating
to linear, geometric and surface texture dimensioning and tolerancing, together with the practice of
welding symbology, limits and fits and thread data. It also includes an illustrated index to all standards
referenced in BS 8888.
This guide does not replace BS 8888 which is the definitive standard for technical product realization.
Any element of BS 8888 not included in this guide should not be considered as less important to
technical specification than those included.
Most of the drawings in this guide have been extracted (and adapted) from the following BSI publications:
BS EN ISO 1101, BS EN ISO 1302, BS ISO 5459, BS 8888 and PP 8888, Parts 1 and 2.
1
Chapter 1
Dimensioning and tolerancing of size
1.1 Introduction
Dimensioning is the process of applying measurements to a technical drawing. It is crucial to the whole
process by which the designer will communicate the information required for the manufacture and
verification of products.
1.2 General principles
Dimensions shall be applied to the drawing accurately, clearly and unambiguously. The following points
shall be regarded as general dimensioning principles to be applied to all technical drawings.
•
•
•
•
•
•
•
•
•
•
•
•
Each dimension necessary for the definition of the finished product shall be shown once only.
Never calculate a dimension from the other dimensions shown on the drawing, nor scale the drawing.
There shall be no more dimensions than are necessary to completely define the product.
Preferred sizes shall be used whenever possible (see notes).
Linear dimensions shall be expressed in millimetres (unit symbol ‘mm’). If this information is stated
on the drawing, the unit symbol ‘mm’ may be omitted. If other units are used, the symbols shall be
shown with their respective values.
Dimensions shall be expressed to the least number of significant figures, e.g. 45 not 45,0.
The decimal marker shall be a bold comma, given a full letter space and placed on the baseline.
Where four or more numerals are to the left or right of the decimal marker, a full space shall divide
each group of three numerals, counting from the position of the decimal marker, e.g. 400 or 100 but
12 500 (see notes).
A zero shall precede a decimal of less than one, e.g. 0,5.
An angular dimension shall be expressed in degrees and minutes, e.g. 20° and 22° 30’ or,
alternatively, as a decimal, e.g. 30,5°.
A full space shall be left between the degree symbol and the minute numeral.
When an angle is less than one degree, it shall be preceded by a zero, e.g. 0° 30’.
NOTES: Preferred sizes are those referring to standard material stock sizes and standard components such as nuts, bolts,
studs and screws.
Decimal marker points or commas are not used to separate groups of numerals. This causes ambiguity since the decimal
marker is denoted by a comma.
2
The Essential Guide to Technical Product Specification: Engineering Drawing
End product: complete part ready for assembly or service, or a configuration prod
1.3 Types of dimension
from a drawing specification. An end product may also be a part ready for fu
processing (for example, a product from a foundry or forge) or a configuration nee
For the purposes of this section, the following definitions apply.
further processing.
dimension
numerical value expressed in appropriate units of measurement and indicated graphically on technical
drawings with lines, symbols and notes
6. Dimensioning of technical drawings
Dimensions are classified according to the following types.
functional dimension
dimension that is essential to the function of the piece or space (‘F’ in Figure 1). See also 1.14
non-functional dimension
dimension that is not essential to the function of the piece or space (‘NF’ in Figure 1)
End product: complete part ready for assembly or service, or a configuration produced
(a) Design requirement
auxiliary dimension
from a drawing specification. An end product may also be a part ready for further
Dimension, given
for information
purposes
only,from
thatadoes
notor
govern
or inspection
processing
(for example,
a product
foundry
forge)production
or a configuration
needing
operations and is derived from other values shown on the drawing or in related documents
further processing.
NOTE: An auxiliary dimension is given in parentheses and no tolerance may be applied to it (‘AUX’
F in Figure
F 1).
NF
feature
end product
complete part ready for assembly or service
NF
or
NF
configuration produced from a drawing specification
(AUX)
or ready for assembly or service, or a configuration
(a) Design requirement
uct: complete part
produced
part ready for further processing (for example, a product from a foundry (b)
or Shoulder
forge) orscrew
a configuration
awing specification. An end product may also be a part ready for further
needing further processing
g (for example, a product from a foundry or forge) or a configuration needing
ocessing.
F
F
F
NF
NF
NF
(a) Design
(a)requirement
Design requirement
F
F
dimensioning
(AUX)
(b)screw
Shoulder screw
(b) Shoulder
Figure 1 – Types of dimensioning
F
F
F
NF
NF
F
F
F
F
NF
NF
F
F
Figure 57: Types of
NF
Threaded hole
(c) Threaded(c)
hole
F
F
F
Figure
individual characteristic such as a flat surface,
a cylindrical surface,
two parallel
surfaces, a shoulder,
a 57: Types of
6. Dimensioning
of technical
drawings
dimensioning
screw thread, a slot or a profile
3
Dimensioning and tolerancing of size
1.4 Dimensioning conventions
Technical product specification standards specify the following conventions when dimensioning drawings.
Extension lines shall normally be placed outside the view to aid clarity, as shown in Figure 2.
The extension line connects the dimension line (on which the value of the measurement is placed)
to the reference points on the outline of the drawing. The following standard practice is specified.
Crossing of extension lines shall be avoided whenever possible.
There should be a small gap between the outline of the drawing and a projection line. The extension
line shall extend slightly beyond the dimension line, as shown in Figure 2.
Extension lines shall, where possible, be drawn at right angles to the dimension line.
Centre-lines, extensions of centre-lines and continuations of outlines shall never be used as
Drawing
practice
dimension
lines. They may, however, be used as projection lines.
Arrowheads and origin circles are commonly used as terminators for dimension lines. Oblique
strokes and points can also be used, as shown in Figures 3 and 4.
Dimension lines shall be unbroken even if the feature they refer to is shown as interrupted, as
illustrated in Figure 5.
6. 6.
Dimensioning
of technical
Dimensioning
6. Dimensioning
of technical
ofdrawings
technical
drawings
draw
Leader line
6. Dimensioning
6. Dimensioning
6. Dimensioning
of technical
of line
technical
of technical
drawings
drawings
drawing
Extension
2 × 45
4500
3500
]
1500
Value of the dimension
When
symmetrical
are drawn
partially,
the portions
of
lines
] When
]symmetrical
When parts
symmetrical
parts
areparts
drawn
arepartially,
drawn
partially,
the portions
thethe
portions
of dimension
the dimension
of the
dimension
lines
lines
Origin indication
Dimension line
Termination (arrowhead)
extend
a short
way way
beyond
the
of symmetry
andsymmetry
the second
extend
aextend
short
a short
beyond
wayaxis
the
beyond
axis
of
thesymmetry
axis of
and
the second
andtermination
thetermination
second istermination
is
is
] When
] When
]symmetrical
When
symmetrical
symmetrical
partsparts
are parts
drawn
are drawn
are
partially,
drawn
partially,
the
partially,
portions
the portions
the of
portions
the
of dimension
the
ofdimension
the dimension
lines lines lines
omitted,
as shown
in Figure
62.
Figure
2inlines
–Figure
Examples
of extension
lines and dimension lines
omitted,
omitted,
asextension
shown
as
shown
62.
Figure
62.
Figure 58:
Examples
of
andin
dimension
lines
extend
extend
a short
extend
a short
way
a short
way
beyond
beyond
waythe
beyond
axis
the of
axis
the
symmetry
of
axis
symmetry
of symmetry
and the
and second
the
andsecond
thetermination
second
termination
termination
is is is
omitted,
omitted,
as
omitted,
shown
as shown
as
in shown
Figure
in Figure
62.
in Figure
62. 62.
Terminators: dimension lines shall be terminated according to one of the representations Figure
shown
in Figure
3. 59:forTerminato
59:
Terminators
Figure
59:
Figure
Terminators
for
6.4 Dimensioning conventions
dimension
linesdimension
dimension
lines
lines
Figure
Figure
59:Figure
Terminators
59: Terminators
59: Terminators
for for fo
(c) Arrowhead,
30° 30° open 30°
(c) Arrowhead,
(c)open
Arrowhead,
open
(b) Arrowhead,
(b)closed
Arrowhead,
closed closed
(a) Arrowhead,
(a) Arrowhead,
(a)closed
Arrowhead,
closed closed(b) Arrowhead,
dimension
dimension
dimension
lines lines lines
30° 30°
30°
and filled
30° (BS
and filled
and
30°8888
filled
(BS 8888
30° (BS 8888
(a) Arrowhead, closed and filled 30°
(b) Arrowhead, closed 30°
Arrowhead,
(c) Arrowhead,
(c) Arrowhead,
(c) (c) Arrowhead,
open
open
30° open
30°open
30°30°
(b) Arrowhead,
(b) Arrowhead,
(b) Arrowhead,
closed
closedclosed
default)
(a)
Arrowhead,
(a) Arrowhead,
(a) Arrowhead,
closed
closedclosed
default)
default)
6.4.1 General
(BS 8888
default)
and filled
and filled
30°
and(BS
filled
30°8888
(BS
30°8888
(BS 8888 30° 30° 30°
default)
default)
default)
Technical product specification standards recommend the following conventions
(d) Arrowhead, open 90° (BS
8888dimensioning
(e) Oblique
stroke
(f) Point (used only if no place for
drawings.
(d) Arrowhead,
90° when
(f) Point
(used(used
only
if no(used
(d) Arrowhead,
(d)open
Arrowhead,
open
90° open
90°Oblique
(e)
stroke
(f) Point
(f)
Point
only
ifthe
nooblique
only if no
(e) Oblique
(e)stroke
Oblique stroke
non-preferred)
arrowhead;
stroke may
(BS 8888
non-preferred)
place
for
arrowhead;
the
(BS 8888 (BS
non-preferred)
8888 non-preferred)
place foralso
arrowhead;
place
be for
usedarrowhead;
– the
BS 8888) the
(d) Arrowhead,
(d) Arrowhead,
(d) Arrowhead,
openopen
90° open
90° 90°(e) Oblique
oblique
stroke
may(used
also
Point
(f) Point
(used
(f) stroke
Point
(used
only
ifonly
nostroke
ifalso
only
no may
if no also
(e) Oblique
(e)stroke
Oblique
strokestroke (f)
oblique
oblique
may
6.4.2 Extension lines and dimension
lines
(BS 8888
(BS 8888
non-preferred)
(BS 8888
non-preferred)
non-preferred)
be used
–arrowhead;
BS
place
place
forused
place
for–8888)
arrowhead;
for
arrowhead;
the
the
be
be
BS
used
8888)
– BSthe
8888)
Figure 3 – Terminators for dimension
lines
oblique
oblique
stroke
oblique
stroke
maystroke
also
may also
may also
The extension line connects the dimension
(on
which
value of the measurebe used
beline
used
– be
BS
used
8888)
– BS
8888)
– BSthe
8888)
ment is placed) to the reference points on the outline of the drawing. The following
standard practice is recommended.
]
Figure
60: Origin
Figure
60:
Figure
Origin60: Origin
indication
indicationindication
Figure
Figure
60:Figure
Origin
60: Origin
60: Origin
Extension lines (continuous narrow line type 01.1.3, see Table 1) should normally
indication
indication
indication
be placed outside of the view to aid clarity, as shown in Figure 58.
]
Crossing of extension lines should be avoided whenever possible.
]
There should be a small gap between the outline of the drawing
and
a projection
interrupted
features
interrupted
interrupted
features features
Figure
61: Dimensioning
Figure
61:
Figure
Dimensioning
61: Dimension
line. The extension line should extend slightly beyond the dimension
line,
as shown
Figure
Figure
61:
Figure
Dimensioning
61:
Dimensioning
61: Dimensioning
dimension lines
(b) Arrowhead, closed
(a) Arrowhead, closed
4
(c) Arrowhead, open 30°
30°Oblique stroke
(d)
open
90°
andArrowhead,
filled 30° (BS
8888
(f) Point (used only if no
(e)
(BS
8888 non-preferred) The Essential Guide to Technical Product
default)
place
for arrowhead;
the
Specification:
Engineering
Drawing
oblique stroke may also
be used – BS 8888)
(d) Arrowhead,
open
Point (used
only if4.no
Origin indication:
the origin
of 90°
the dimension
line shall
be indicated as(f)shown
in Figure
(e) Oblique
stroke
(BS 8888 non-preferred)
place for arrowhead; the
oblique stroke may also
be used – BS 8888)
Figure 60: Origin
indication
Figure 4 – Origin indication
Figure 60: Origin
Figure 61: Dimensioning
indication
interrupted features
Figure 61: Dimensioning
interrupted features
Figure 5 – Dimensioning interrupted features
Figure 62: Dimension lines
on a partial view of a
When symmetrical parts are drawn partially, the portions of the dimension lines shall extend a short way
symmetrical part
beyond the axis of symmetry and the second termination shall be omitted, as shown in Figure 6.
Figure 62: Dimension lines
on a partial view of a
symmetrical part
69
Figure 6 – Dimension lines on a partial view of a symmetrical part
1.5 Arrangement of dimensions
The way in which dimensions are typically used on drawings is shown in Figure 7. Conventions for
arranging dimensions on drawings are as follows.
Dimensions shall be placed in the middle of the dimension line above and clear of it.
Dimensions shall not be crossed or separated by other lines on the drawing.
Values of angular dimensions shall be oriented so that they can be read from the bottom or the
right-hand side of the drawing, as shown in Figure 8.
Where space is limited, the dimension can be placed centrally, above, or in line with, the extension
of one of the dimension lines, as shown in Figure 9.
Larger dimensions shall be placed outside smaller dimensions, as shown in Figure 10.
69
]
Where space is limited, the dimension can be placed centrally, above, or in line
with, the extension of one of the dimension lines (see Figure 66).
]
Larger dimensions are placed outside smaller dimensions (see Figure 67).
]
Dimensions of diameters should be placed on the view that provides the greatest
6. Dimensioning of technical5drawings
Dimensioning and tolerancing of size
clarity (see Figure 68).
Dimensions of diameters shall be placed on the view that provides the greatest clarity, as shown in
Figure 11.
Figure 64: Orientation of
Figure 63: Examples of the
60
ways in which dimensions
linear dimensions
30
are typically used on
60
60
drawings
30
6. Dimensioning of technical drawings
60
60
Figure 7 – Examples of the ways in which dimensions are typically
used on drawings
(a)
60
60
Figure 64: Orientation of
Figure 65: Orientation of
angular dimensions
30
linear 3dimensions
0
60
60
60
60
70
30
Drawing practice
Drawing practice
30
60
60
(a)
60
60
(b)
Figure 8 – Orientation of linear and angular dimensions
60
Figure 66: Dimensioning
Figure 66: Dimensioning
smaller features
smaller features
3
3
6
6
60
60
30
60
3 Orientation of
Figure30
65:
3
3
3
angular dimensions
Figure 9 – Dimensioning smaller 60
features
60
30
90
90
30
Figure 67: Larger
Figure 67: Larger
dimensions placed outside
dimensions placed outside
smaller dimensions
smaller dimensions
6
6
60
60
12
12
50
50
60
60
3
3
5050
(a)
3838
(b)
60
30
Figure 10 – Larger dimensions placed outside smaller dimensions
60
71
60
60
0
5
(b)
60
5
60
60
5
Figure 68: Dimensions of
Figure 68: Dimensions of
diameters placed on view
diameters placed on
30view
providing the greatest
providing the greatest
clarity
clarity
38
50
6. Dimensioning of technical drawings
6
The Essential Guide to Technical Product Specification: Engineering
6. Drawing
Dimensioning of tech
ure 68: Dimensions of
60
meters placed on view
Figure 69: Parallel
oviding the greatest
dimensioning
rity
Figure 6
420
50
45
65
150
35
dimensio
150
640
420
640
Figure 11 – Dimensions of diameters placed on view providing greatest clarity
Superimposed running dimensioning is a simplified parallel dimensioning and may
Dimensioning
from
a common feature
be used where a number
of dimensions of the same direction
6.6
Examples
ofcandimensioning
methods
be used where
space limitations. The common origin is shown as in Figure 70.
relate to a common
origin.there are
Superimposed running dimensioning is a simplified parallel dimensioning and may
Dimension
may be:
Dimensioning
fromvalues
a common
maythere
be executed
parallel dimensioning
as superimposed
be feature
used where
are spaceaslimitations.
The common or
origin
is shown as in Figure 70.
running dimensioning.
Dimensioning from a common feature is used where a number of dimensions of the
Dimension values may be:
]
Parallel same
dimensioning
isrelate
theofplacement
of aorigin.
number
of
single
dimension
paralleldrawings
to one another
above
and clear
dimension
line 6.
(seeDimensioning
Figure
70a);
or of lines
technical
direction
tothe
a common
and spaced ]outinsoline
that
the
dimensional
value
can
easily
be
added
in,
as
shown
in
Figure
12a.
with the corresponding
extension line (see Figure 70b).
] above and clear of the dimension line (see Figure 70a); or
Superimposed running dimensioning is a simplified parallel dimensioning and may be used where
Dimensioning from a common
feature
may
be executed as
parallel dimensioning
or70b).
as
] in line
with is
the
extension
line (see values
Figure
there are space limitations. The common
origin
ascorresponding
shown in Figure
12. Dimension
may be above
and clear ofsuperimposed
the dimensionrunning
line, asdimensioning.
shown in Figure 12b; or in line with the corresponding extension line,
as shown in Figure 12c.
Figure 70: Examples of
Parallel dimensioning is the placement of a number of single dimension lines parallel running dimensioning
to one another and spaced out so that the dimensional value canFigure
easily69:
be Parallel
added in
dimensioning
(see Figure 69).
150
150
420
420
640
a)
running
640
150
(a)
Figure 7
420
(a)
640
b)
Superimposed running dimensioning is a simplified parallel dimensioning and may
be used where there are space limitations. The common origin is shown as in Figure 70.
c)
640
(b)
420
in line with the corresponding extension line (see Figure 70b).
640
]
150
above and clear of the dimension line (see Figure 70a); or
150
]
420
Dimension values may be:
Figure 12 – Parallel dimensioning
and running dimensioning
Figure 70: Examples of
(b)
running dimensioning
73
Drawing practice
Chain dimensioning consists of a chain of dimensions. These should only be used
where the possible accumulation of tolerances does not affect the function of the part
7
Dimensioning
andFigure
tolerancing
(see
71). of size
Chain dimensioning consists of a chain of dimensions. These should only be used
Combined dimensioning uses chain dimensioning and parallel dimensioning on the
where the possible accumulation of tolerances does not affect the function of the part
same
drawing
(see Figure
72).of of
Chain
dimensioning
consists
a chain ofThese
dimensions.
These
only be
Chain dimensioning
consists
dimensions.
shall only
be should
used where
theused
possible
(see
Figure
71). of a chain
accumulationwhere
of tolerances
does
not affect the
ofdoes
the part,
as shown
in Figure
the possible
accumulation
of function
tolerances
not affect
the function
of 13.
the part
Combined
uses chain dimensioning and parallel dimensioning on the
(see Figuredimensioning
71).
Figure 71: Chain
100
same drawing (see Figure 72).
Combined dimensioning uses chain dimensioning and parallel dimensioning on the
dimensioning
same drawing (see Figure 72).
150
100
Figure 71: Chain
dimensioning
160
70
200
Figure 13 – Chain dimensioning
Figure 72: Examples of
160
70
200
30
150
dimensioning
150 100
Figure 71: Chain
30
combined dimensioning
Combined dimensioning uses chain dimensioning and parallel dimensioning on the same drawing view.
160dimensions
70 and parallel
200 dimensioning
30 from a common feature.
Figure 14a illustrates combining single
Figure 14b illustrates combining single dimensions and chain dimensions.
Figure 72: Examples of
combined dimensioning
Figure 72: Examples of
combined dimensioning
(a) Combining single dimensions and parallel
dimensioning from a common feature
(a) Combining single dimensions and parallel
dimensioning from a common feature
a)
(a) Combining single dimensions
and parallel
dimensioning from a common feature
(b) Combining single dimensions and chain dimensions
b)
(b) Combining single dimensions and chain
dimensions
74
Figure 14 – Combined dimensioning
(b) Combining single dimensions and chain dimensions
74
74
Dimensioning by coordinates uses superimposed running dimensioning in two direcThe Essential
Guide
Technical
Product
Engineering Drawing
tions at right angles, as shown
in Figure
73. to
The
common
originSpecification:
may be any suitable
Dimensioning by coordinates uses superimposed running dimensioning in two direccommon reference feature. It may be useful, instead of dimensioning as shown in
tions at right angles, as shown in Figure 73. The common origin may be any suitable
Figure 73, to tabulate dimensional values as shown in Figure 74.
common reference feature. It may be useful, instead of dimensioning as shown in
Dimensioning by coordinates uses superimposed running dimensioning in two directions at right angles,
Figure 73, to tabulate dimensional values as shown in Figure 74.
as shown in Figure 15a. The common origin may be any suitable common reference feature. It may be
useful, instead of dimensioning as shown in Figure 15a, to tabulate dimensional values as shown in
Figure 73: Dimensioning
Figure 15b.
∆
15
,5
8
∆
11
120
∆
∆
13
,5
∆
13
13
,5
20
,5
∆
∆
60
13
13
,5
∆ ∆
13 26
,5
∆
13
,5
,5
90
60
∆
26
∆
13
,5
∆
26
120
90
∆
15
,5
∆ ∆1
26 5,
5
∆
11
160
directions)
∆
15
,5
160
∆
15
,5
∆
15
,5
by coordinates (two
Figure
73: Dimensioning
directions)
by coordinates (two
140
180
200
140
180
200
60
60
100
20
20
100
0
0
0
200
a) in two directions
Figure 74: Dimensioning
A2
A2
B2
B2
B1
Y
A1
Y
A1
by coordinates (tabulated)
Figure 74: Dimensioning
by coordinates (tabulated)
C
∆
C
B1
∆
120
90
X
X
160
60
120
160
90
60
b) tabulated
Figure 15 – Dimensioning by coordinates
75
75
A diameter of a circle or cylinder is dimensioned by prefixing the value with the symbol
Ø. This symbol should be as large as the following numerals and the slanting line
9
tolerancing
of size
should be aboutDimensioning
30° clockwiseand
from
the vertical,
in the direction in which it is to be read
(see Figure 68). It has already been pointed out (see Figure 68) that the dimensions
should be placed on the view that most clearly shows the information.
1.6 Methods for dimensioning common features
Where dimension lines and other lines (e.g. extension lines) would otherwise intersect,
the dimension Certain
lines tofeatures,
the feature
be dimensioned
by leaderhole
linessizes,
as shown
suchcan
as diameters,
radii, squares,
chamfers, countersinks and counter-bores,
can
occur
frequently
in
engineering
drawings.
in Figure 75. Where the whole view is not shown, concentric diameters can be
A diameter of a circle or cylinder shall be dimensioned by prefixing the value with the symbol Ø,
dimensioned as in Figure 76.
as shown in Figure 16. A square feature shall be dimensioned by prefixing the value with the symbol .
Additionally, square and flat features can be indicated by continuous narrow lines drawn diagonally on
Circles are to be dimensioned as shown in Figure 77 and spherical surfaces as shown in
the flat feature, as shown in Figure 18.
Figure 78.
Where dimension lines and other lines (e.g. extension lines) would otherwise intersect, the
dimension lines to the feature can be dimensioned by leader lines as shown in Figure 16.
Where the whole view is not shown, concentric diameters shall be dimensioned as in Figure 17.
6. Dimensionin
25
12. Dimensionin
340
320
300
20
Figure 78: Radial values
R1
0
35
R1
5
30
370
55
Figure 16 – Diameter dimensions
indicated by leader lines
Figure 17 – Dimensioning concentric
diameters on a partial view
20
10
10
40
Figure 79: Square values
NOTE. Leader line should
be in line with centre
of circle
40
Figure 18 – Dimensioning a square
SR6
0
SR
12
Figure 80: Spherical radi
Circles shall be dimensioned as shown in Figure 19 and spherical surfaces as shown in Figure 20.
Radii of features shall be dimensioned by prefixing the value with the letter R. Radii shall bevalues
dimensioned by a line that passes through, or is in line with, the centre of the arc. The dimension line
shall have one arrowhead only, which shall touch the arc.
S∆50
Radii that require their centres to be located shall be dimensioned as in Figure 21a; those that do
not shall be dimensioned as in Figure 21b. Spherical radii shall be dimensioned as shown in Figures 21c
and 21d.
S
20
370
Drawing
practice
10
Drawing practice
The Essential Guide to Technical Product Specification: Engineering Drawing
Drawing practice
Drawing practice
S∆50
S∆50a
Figure 77: Dimensioning
20
10
spherical
circle
10
Figure 78
6.7.3 Radii
6.7.3 Radii
Radii of features are dimensioned by prefixing the value with the letter R. Radii should
Radii of features are dimensioned by prefixing the value with the letter R. Radii should
NOTE. Leader line should
be dimensioned
a line that passes through, or is in line with, the centre of the arc.
6.7.3 by
Radii
be in line with centre be dimensioned
by
a
line that passes through, or is in line with, the centre of the arc.
6.7.3line
Radii
The dimension
should have one arrowhead only, which should touch the arc.
of circle
20 value
The dimension
should
have
one arrowhead
only,Swhich
touch
arc.
S 20 by prefixing
Radiiline
of features
are dimensioned
the
the the
letter
R. Radii should
40
shouldwith
Radii
of
features
are
dimensioned
by
prefixing
the
value
with
the
letter
R. Radii should
Radii that require
their centres
bethat
located
be dimensioned
as in Figure
79a;
(a) should
be dimensioned
line
passes
through,
or is in line with,
the centre
of the arc.
(a)by ato
a)
b)
(b)
Radii that require
their centres
toline
be that
located
should
be dimensioned
as
in Figure
79a; of the arc.
(b)
be
dimensioned
by
a
passes
through,
or
is
in
line
with,
the
centre
those that The
do not
are dimensioned
as in
Figure
Spherical
radiiwhich
are dimensioned
asthe arc.
dimension
line should
have
one79b.
arrowhead
only,
should touch
those that do
not
are dimensioned
as in
Figure
79b.
Spherical
radii
are dimensioned
as the arc.
Figure
20
–
Dimensioning
The
dimension
line
should
have
one
arrowhead
only,
which
should
touch
shown in Figures 79c and 79d.
spherical
diameters
shown in Figures
79crequire
and 79d.
Radii that
their centres to be located
should be
dimensioned as in Figure 79a;
Radii that require their centres to be located should be dimensioned as in Figure 79a;
Figure 19 – Dimensioning
a diameter
those that
do not are dimensioned as in Figure 79b. Spherical radii are dimensioned as
Holes
are to be
dimensioned
as shown
Figure
depth
the
Holes
aredo
to not
be dimensioned
as shown
in Figure
79.Spherical
Theindepth
of79.
the
drilled
holeofwhen
those
that
are
dimensioned
as in Figure
79b.
radii
areThe
dimensioned
as drilled hole w
shown in Figures 79c and 79d.
given
in note
form
refers
to the
depth of
the cylindrical
portion
of the
given in
in Figures
noteS∆
form
refers
to the
depth
ofFigure
the
cylindrical
portion
of the hole
and not
to hole and n
shown
79c
and
79d.
78: Dimensioning
50
the extremity
made
by the
point
of otherwise
the drill, unless
R5,5
spherical
diameters
the extremity made
by the point
of
the
drill,
unless
specified.
R4 otherwise specified.
R5,5
R4
R4
R4
R2
R2
S 20
R8
R8
(a)
R100
R100
(b)
R2
R2
R8
R8
b)
given in note form refers to the depth of the cylindrical portion of the hole and not to
he extremity made by the point of the drill, unless otherwise specified.
SR6SR
0 60
12 12
c)
Figure 79: Dimensioning radii
Figure 79: Dimensioning radii
Figure 79: Dimensioning radii
Figure 79: Dimensioning radii
(d)
(d)
Figure 21 – Dimensioning radii
d)
(d)
(d)
SR6SR60
0
(c)
(c)
SR SR
77
SR20
SR20
(c)
(c)
SR SR
12 12
SR S
R
12 12
SR20
SR20
(b)
(b)
SR S
R100
12 R1 R100
2
(b)
(a)
a)
(b) hole when
Holes are to be dimensioned
as shown in Figure
79. The depth of the drilled
(a)
78
78
R4
R4
5 25
R2 R
(a)
(a)
R4
R4
5 5
R2 R2
R5,5
R5,5
13
Holes Holes
are dimensioned
are dimensioned
as shown
as shown
in Figure
in Figure
80. The
80.depth
The depth
of theofdrilled
the drilled
hole, hole,
whenwhen
given given
after the
afterdiameter,
the diameter,
refersrefers
to thetodepth
the depth
of theofcylindrical
the cylindrical
portion
portion
of theofhole
theand
hole and
not tonot
thetoextremity
the extremity
mademade
by thebypoint
the point
of theofdrill,
the unless
drill, unless
otherwise
otherwise
specified.
specified.
11
Dimensioning and tolerancing of size
∆32
+ 0,02
0
FigureFigure
80: Dimensioning
80: Dimensioning
4 × ∆54 × ∆5
6.7.4 Holes
∆7
∆7
holes holes
Teacher’s note: the method of production (e.g. drill, punch, bore or ream) sh
Holes shall be dimensioned as shown in Figure 22. The depth of the drilled hole, when given after the
not
be specified
is essential
the function of the drawing.
Holestoare
shown in
Figure
80. Theexcept
depth where
of the itdrilled
hole, to
when
diameter, refers
thedimensioned
depth of theas
cylindrical
portion
∆ 38 ∆of38the hole and not to the extremity made by the
theotherwise
diameter,specified.
refers to the depth of the cylindrical portion of the hole and
point of thegiven
drill, after
unless
The method
production
punch,
or drill,
ream)unless
shall otherwise
not be specified
except where it is
not toofthe
extremity (e.g.
madedrill,
by the
pointbore
of the
specified.
essential to the function of the part.
+ 0,02 + 0,02
+ 0,5
0
+ 0,5
0
13
13
∆9,5 ×∆18
9,5 × 18
∆32 arcs
0∆32 and
0
6.7.5 Chords,
angles
Figure 80: Dimensioning
4 × ∆5
The dimensioning of chords,
as shown in Figure 81
∆7arcs and angles should beholes
∆32
6.7.56.7.5
Chords,
Chords,
arcs arcs
and angles
and angles
105
13
100
+ 0,5
0
∆9,5 × 18
Teacher’s
Teacher’s
note: note:
the method
the method
of production
of production
(e.g. drill,
(e.g.punch,
drill, punch,
bore or
bore
ream)
or ream)
shouldshould
Drawing practice
∆ 38
not benot
specified
be specified
exceptexcept
wherewhere
it is essential
it is essential
to thetofunction
the function
of theofdrawing.
the drawing.
+ 0,02
0
Figure 22 – Dimensioning holes
The dimensioning
The dimensioning
of chords,
of chords,
arcs and
arcsangles
and angles
should
should
be asCurved
be
shown
as shown
insurfaces
Figure
in Figure
81. 81.
6.7.6
(b) Arc
(a) Chord
Teacher’s note: the method of production (e.g. drill, punch, bore or ream) should
The dimensioning of chords, arcs and angles shall be as shown in Figure 23.
not be specified except where
it is essential
to thethe
function
of of
theholes
drawing.
When
dimensioning
spacing
and other features on a curved surf
100
whether the
dimensions
are chordal or
circumferential,
they are to be indicated cle
Figure
Figure
81:
81: Dimensioning
105
105
42Dimensioning
100
chords,chords,
arcs and
arcsangles
and angles
on the drawing, as shown in Figure 82.
6.7.5 Chords, arcs and angles
Figure 82: Dimensions on
tice
nsions on
800 OUTER SURFACE
The
dimensioning
arcs and angles should be as
a curved
surface of chords,
shown in Figure 81.
(b) Arc(b) Arc
(a) Chord
(a) Chord
a) chord
(c) Angle
b) arc
Figure100
23 – Dimensioning chords, arcs and
105angles
42
c) angle
Figure 81: Dimensioning
chords, arcs and angles
42
Dimensioning the spacing of holes and other features on a curved surface shall be as shown in Figure 24,
whethersurfaces
the dimensions are chordal or circumferential, they shall be indicated clearly on the drawing.
6.7.6 Curved
When dimensioning the spacing
of holes and other features on a(b)
curved
Arc surface,
(a) Chord
(c) Angle
(c)
whether the dimensions are chordal
or Angle
circumferential, they are to be indicated clearly
on the drawing, as shown in Figure 82.
42
800 OUTER SURFACE
79
79
(c) Angle
75 +- 0,5
Figure 24 – Dimensions on a curved surface
6.8 Dimensioning screw threads and threade
parts
of technical drawing
6.8.2
Thread
size6.of Dimensioning
The Essential
Guide
to Technical
Product
Specification:
Engineering
Drawing
6.system
Dimensioning
6. and
Dimensioning
technical
of technical
drawings
drawings
12
6. Dimensioning
of technical
drawings
6. Dimensioning
of technical
drawings
The letter M, denoting ISO metric screw threads, is followed by the values of th
nominal diameter and pitch (if required), with a multiplication sign between them
1.7 Dimensioning screw threads and
threaded parts
e.g. M8 × 1.
ISO metric screw threads shall be designated in accordance with BS EN ISO 6410-1, which specifies
6.8.2
Thread
system
and size
6.8.2
6.8.2
Thread
system
system
and
size
and
size
6.8.3
Thread
class
that Thread
the
designation
shall
indicate
the
thread
system,
nominaltolerance
diameter and
the thread tolerance class. If
6.8.2
Thread
system
and
size
6.8.2 Thread system and size
necessary, the pitch shall also be indicated; however, when designating metric coarse threads, the pitch
The letter M, denoting ISO metric screw threads, is followed by the values of the
Theisletter
TheM,
letter
denoting
M, denoting
ISO metric
ISO screw
metricthreads,
screwFor
threads,
isgeneral
followed
isuse,
followed
bythe
thetolerance
values
by the of
values
the 6H
of isthe
class
suitable for internal threads and toleranc
generally
omitted.
The
letter
M, denoting
ISO metric
screw
threads,
is followed
byvalues
the values
of the
The letter M,nominal
denoting
ISO metric
screw
threads,
is followed
by the
of the
diameter
and
pitch
(if
required),
with
a
multiplication
sign
between
them,
The
nominal
diameter
to
major
diameter
ofexternal
external
and
threads;
the dimension
nominal
nominal
diameter
diameter
and
pitch
and(ifrefers
pitch
required),
(if the
required),
with
aclass
multiplication
with6g
a for
multiplication
sign threads.
between
signinternal
between
them,
them,
The
thread
tolerance
class is preceded by a hyphen, e.g
nominal
diameter
and pitch
(if required),
with
a multiplication
sign between
them,
nominal
diameter
and
pitch
(if
required),
with
a
multiplication
sign
between
them,
e.g. of
M8thread
× 1. refers to the full depth of thread. The direction of a right hand thread (RH)
to
the×depth
e.g.relating
M8e.g.
× 1.
M8
1.
M10-6H or M10 × 1-6g.
e.g.
M8
×
1.
e.g.
M8
×
1.
is not generally noted; however left hand threads shall be denoted with the abbreviation ‘LH’ after the
thread designation.
6.8.3 Thread toleranceScrew
classthreads are dimensioned as shown in Figures 83 and 84.
6.8.3 Thread
6.8.3 Thread
tolerance
tolerance
class class
6.8.3
Thread
6.8.3
Thread
classclass
Thread
system
andtolerance
sizetolerance
M36-6g
M20-6g
For general
use, the
tolerance
class 6Hbe
is followed
suitable for
threads
tolerance
letter
M, denoting
ISO
metric
threads,
by internal
the
values
of theand
nominal
diameter
ForThe
general
For general
use,
theuse,
tolerance
the
tolerance
class
6Hscrew
class
is suitable
6H
is suitable
for shall
internal
for internal
threads threads
and
tolerance
and
tolerance
For
general
use,
the
tolerance
class
6H
is
suitable
for
internal
threads
and
tolerance
For
general
use,
the
tolerance
class
6H
is
suitable
for
internal
threads
and
tolerance
and pitch (if required),
with
multiplication
them, e.g.
M8
× 1.
class 6g
foraexternal
threads.sign
The between
thread tolerance
class
is preceded
by a hyphen, e.g.
class 6gclass
for external
6g for external
threads.threads.
The thread
The tolerance
thread tolerance
class is preceded
class is preceded
by a hyphen,
by a hyphen,
e.g.
e.g.
class
for external
threads.
The thread
tolerance
class
is preceded
by a hyphen,
class 6g
for6g
external
threads.
The
thread
tolerance
class
is
preceded
by
a
hyphen,
e.g. e.g.
M10-6H or M10 × 1-6g.
40
30 min
M10-6H
M10-6H
or tolerance
M10 or
× M10
1-6g.
× 1-6g.
Thread
class
M10-6H
or M10
× 1-6g.
M10-6H
or M10
× 1-6g.
full
For general use, the tolerance class 6H is suitable for internal threads and tolerance class 6g for external thread
Screw
threadsclass
are dimensioned
as shown
Figures 83 and 84.
threads.
Thethreads
thread
tolerance
shall
be
preceded
by83
a in
hyphen,
Screw
threads
Screw
are
dimensioned
are
dimensioned
as shown
as in
shown
Figures
in Figures
83 and
84.
and 84. e.g. M10-6H or M10 × 1-6g.
Screw
threads
are
dimensioned
as
shown
in
Figures
83
and 84.
Screw threads are dimensioned as shown in Figures 83 and 84.
Screw threads shall be dimensioned as shown in Figures 25 and 26.
M20-6g
M20-6g
M20-6g
M20-6g
M20-6g
40
M36-6g
M36-6g
(a)
(a) (a)
Figure 83: Dimensioning
(b)
30 min Figure 83:
Figure
Dimensioning
83: Dimensioning
30 min 30 min
Figure
83:
Dimensioning
Figure
83:
Dimensioning
external
screw threads
30 min30 min full thread
external external
screw threads
screw threads
full thread
full thread
external
screw
threads
external screw threads
full thread
full thread
40
40
40
M12-6H x 16 38 max
38 max 38
15max
min
38 max38 max
(b)full thread
(b)
(b)
(b) (b)
(a)
a)
b)
Figure 25 – Dimensioning external screw threads
(a)
(a)
a)
(a)
(a)
(b) b) (b)
(b)
16
16
(a)
16
(b)
Figure 84: Dimensioning
Figure 84:
Figure
Dimensioning
84: Dimensioning
M12 x 1,25-6H FigureFigure
84:
Dimensioning
84: Dimensioning
internal
screw threads
M12 x 1,25-6H
M12 x 1,25-6H
internal screw
internal
threads
screw threads
x 1,25-6H
M12 xM12
1,25-6H
internal
threads
internal
screw screw
threads
1616
(a)
M12-6H x 16
M12-6H M12-6H
x 16
x 16
1516min
M12-6H
x
M12-6H
x
16
15 min 15 min
full thread
15
min
15
full thread
fullmin
thread
full thread
full thread
M12 x 1,25-6H
16
(a)
M36-6g
M36-6g
M36-6g
40
38 max
(a)
(b)
(b)
M6-6H x 10
20 min full thread
c) including run-out
28 max
(c)
Figure 26 – Dimensioning internal screw threads
M6-6H x 10
M6-6H xM6-6H
10
x 10
20
M6-6H
x
10 min full thread
M6-6H
x
10
20 min full
20 thread
min full thread
28thread
max including run-out
20
min
full
20
min
full
thread
28 max including
28 max including
run-out run-out
max
including
run-out
28 max28including
run-out
(c)
(c)
(c)
(c) (c)
81
81
81 81
8
1
45°, the indications may be simplified as shown in Figures 104 and 105.
Note. Methods of production (e.g. ‘drill’, ‘punch’, ‘bore’, ‘ream’)+should
not be
0,02
specified, except where they are essential to the function.
∆32
0
Dimensioning and tolerancing of size
∆13
or
4 × ∆5
13.7 Chamfers and countersinks ∆7
30 ˚
1.8 Dimensioning chamfers and
2
∆9,5 × 18
countersinks
Figure13
103: Chamfer
dimensioning
Figure 102: Hole
dimensioning
30 ˚
13
+ 0,5
0
Chamfers should be dimensioned as shown in Figure 103. Where
∆ 38 the chamfer angle is
Chamfers shall be dimensioned as shown in Figure 27. Where the chamfer angle is 45°, the indications
45°, the indications may be simplified as shown in Figures 104 and 105.
may be simplified as shown in Figure 28.
Figure 104: 45° chamfer
2 × 45 ˚
+ 0,02
∆32 0
30 ˚
simplified
Figure 103: Chamfer
∆13
or or
dimensioning
13.7 Chamfers and countersinks
30 ˚
2
2 × 45 ˚
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.
22××45
45˚ ˚
2 × 45 ˚
Figure 105: Dimensionin
Figure 104: 45° chamfer
internal chamfers
simplified
Figure 103: Chamfer
or
or or
∆13
dimensioning
30 ˚
2 × 45 ˚
30 ˚
2
Figure 27 – Dimensioning external and internal chamfers
Figure 105: Dimensionin
2 × 45 ˚
2 × 45 ˚
2 × 45 ˚
or
internal
chamfers
Figure 104:
45° chamfer
simplified
113
or
Engineering drawing practice
2 × 45 ˚
Figure 28 – Simplified dimensioning of chamfers
2 × 45 ˚
Figure 105: Dimensionin
internal chamfers
Countersinks are dimensioned by showing either the required diametral dimension
at
2 × 45 ˚
Countersinks shall be dimensioned by showing either the required diametral dimension at the included
the included angle, or the depth and the included
angle
113 (see Figure 106).
or
angle, or the depth and the included angle, as shown in Figure 29.
Figure 106: Dimensioning
90 ˚
90 ˚
∆14
countersinks
or
113
3,5
Figure 29 – Dimensioning countersinks
13.8 Other indications
The use of reference letters in conjunction with an explanatory note or table can also be
50
13.5 Equally spaced repeated features
14
The Essential Guide to Technical Product Specification: Engineering Drawing
Where repeated features are linearly spaced, a simplified method of dimensioning may
13.5 Equally spaced repeated features
be used, as illustrated in Figure 95.
1.9 Equally spaced repeated features
Where
features areone
linearly
spaced,
a simplified
method of dimensioning
may
If thererepeated
is any ambiguity,
feature
space
may be dimensioned
as illustrated
in
be
used,
as
illustrated
in
Figure
95.
Where repeated
are linearly spaced, a simplified method of dimensioning may be used, as
Figurefeatures
96.
shown in Figure 30.
If there is any ambiguity, one feature space may be dimensioned as illustrated in
ure 95: Dimensioning
inear spacings
Figure 96.
ure 95: Dimensioning
inear spacings
15
5 × 18 (= 90)
Figure 30 – Dimensioning of linear spacings
15
5 × 18 (= 90)
ure 96: Dimensioning
inear spacings If
to there
avoid is any ambiguity, one feature space may be dimensioned as illustrated in Figure 31.
nfusion
ure 96: Dimensioning
inear spacings to avoid
18
nfusion
17 × 18 (= 306)
15
18
17 be
× 18dimensioned
(= 306)
15 equally spaced features may
Angular,
as illustrated in Figure 97.
13. Dimensioning from a common feature
Figure
Dimensioning
of linear
spacings
to avoid
confusion
The angles
of 31
the –spacings
may be omitted
when
the intent
is evident,
as shown in
Angular,
equally
spaced
features
may
be
dimensioned
as
illustrated
in
Figure
97.
Figure 98.
Angular, equally
spaced
shall
bebedimensioned
asindirectly
shown
in
32. The
of of
the
The
angles
offeatures
the
spacings
may
be
omitted when
the intent
is evident,
shown
in spacings
Circular
spaced
features
may
dimensioned
byFigure
specifying
theasangle
number
can be omitted
where
the intent is explicit, as shown in Figure 33.
Figure
98.features,
common
as illustrated in Figure 99.
Circular spaced features may be dimensioned indirectly by specifying the number of
common features, as illustrated in Figure 99.
15
˚
Figure 97: Dimensioning
of angular spacings
110
10 ˚ 3
0'
110
5 × 10 ˚ 30' (52 ˚ 30')
Figure 32 – Dimensioning angular spacing
∆50
Figure 98: The omission of
angles of spacings to avoid
confusion
4 × ∆9
15
˚
Figure 97: Dimensioning
10 ˚ 3
0'
of angular spacings
15
Dimensioning and tolerancing of size
5 × 10 ˚ 30' (52 ˚ 30')
15
˚
∆50
10 ˚ 3
0'
Figure 98: The omission
angles of spacings to avo
confusion
5 × 10 ˚ 30' (52 ˚ 30')
4 × ∆9
∆50
Figure 98: The omission
angles of spacings to avo
confusion
4 × ∆9
5×
Figure 33 – Omission of angle
of spacing
16
Figure 99: Dimensioning
circular spacings
6
Circular spaced features can be dimensioned
indirectly by specifying the number of common features as
shown in Figure 34.
Figure 99: Dimensioning
5×
16
circular spacings
6
5 × ∆12
5 × ∆12
111
Figure 34 – Dimensioning circular spacings
111
16
The Essential Guide to Technical Product Specification: Engineering Drawing
Series or patterned features of the same size may be dimensioned as illustrated in
Figuresor100
and 101.
Series
patterned
features of the same size may be dimensioned as illustrated in
Figures 100
and of
101.
Series or patterned
features
the same size may be dimensioned as illustrated in Figures 35 and 36.
ure 100: Defining a
antity of elements of the
ure 100: Defining a
me size: linear
antity of elements of the
8 × ∆8
8 × ∆8
me size: linear
Figure 35 – Dimensioning a quantity of features of the same size – linear
ure 101: Defining a
6 × ∆8
antity of elements of the
ure 101: Defining a
me size: circular
antity of elements of the
6 × ∆8
me size: circular
13.636Holes
Figure
– Dimensioning a quantity of features of the same size – circular
13.6 Holes
Holes are dimensioned as shown in Figure 102. The depth of the drilled hole, when
1.10 Dimensioning
of curved
profiles
given after
the diameter,
referinto
the depth
of the
cylindrical
of thewhen
hole
Holes
are dimensioned
asshall
shown
Figure
102. The
depth
of the portion
drilled hole,
and not
to the
the diameter,
extremity made
by the
point
of the
unless otherwise
specified.
given
after
shall
tobe
the
depth
of drill,
the by
cylindrical
hole37.
Curved profiles
composed
of circular
arcsrefer
shall
dimensioned
radii, asportion
shown of
inthe
Figure
and not
to thepoints
extremity
by surface,
the pointasofshown
the drill,
unless otherwise
specified.
Coordinates
locating
on amade
curved
in Figure
38, shall only
be used when
the profile is not composed of circular arcs. The more coordinates specified, the better the uniformity of
the curve.
112
112
12.9.
Curved profiles composed of circular arcs should be dimensioned by radii, as illustrated
17
Dimensioning and tolerancing of size
in Figure 118.
Figure 118: The
dimensioning of a curved
profile
Engineering drawing practice
Figure 37 – Dimensioning of a curved profile
Figure 119: Linear
coordinates of a series of
points through which a
profile passes
119
Figure 38 – Linear coordinates of a series of points through which a profile passes
Coordinates locating points on a curved surface, as illustrated in Figure 119, should
1.11 Dimensioning of keyways
only be used when the profile is not composed of circular arcs. The more coordinates
specified,
the uniformity
Keyways in hubs or shafts
shallthe
bebetter
dimensioned
by oneofofthe
thecurve.
methods shown in Figure 39.
NOTE: Further information on keys and keyways is given in BS 4235-1, Specification for metric keys and keyways – Part 1:
Figure
120 illustrates
a method
specifying
a cam
in association
with a
Parallel and taper keys and
BS 4235-2,
Specification
for metricof
keys
and keyways
– Partprofile
2: Woodruff
keys and keyways.
follower. The follower is indicated by a long-dashed double-dotted narrow line type
05.1.1 (see Table 1).
Figure 120: Specifying
dimensions in association
with a follower
0˚
b
shown in Figure 5.
NOTE Further information on keys and keyways is given in BS 4235-1,
Specification for metric keys and keyways – Part 1: Parallel and taper
keys, and BS 4235-2, Specification for metric keys and keyways –
Part 2: Woodruff keys
and
keyways.
The
Essential
Guide to Technical Product Specification: Engineering Drawing
18
Figure 5
Dimensioning of keyways
a) Parallel hub
d) Parallel shaft
f) Parallel shaft
b) Tapered keyway in parallel hub
c) Parallel keyway in tapered hub
e) Parallel keyway in tapered shaft
g) Tapered shaft
Figure 39 – Dimensioning of keyways
1.12 Tolerancing
© BSI 2006 •
21
Tolerancing is the practice of specifying the upper and lower limit for any permissible variation in the
finished manufactured size of a feature. The difference between these limits is known as the tolerance
for that dimension.
All dimensions (except auxiliary dimensions) are subject to tolerances.
Tolerances shall be specified for all dimensions that affect the functioning or interchange ability of
the part.
Tolerances shall also be used to indicate where unusually wide variations are permissible.
Tolerances shall be applied either to individual dimensions or by a general note giving uniform or
graded tolerances to classes of dimensions, for example:
TOLERANCE UNLESS OTHERWISE STATED LINEAR ±0,4 ANGULAR ±0° 30’
The method shown in Figure 40a should be followed where it is required to tolerance individual linear
dimensions. This method directly specifies both the limits of the size of the dimension, the tolerance
being the difference between the limits of the size.
The larger limit of the size shall be placed above the smaller limit and both shall be given to the
same number of decimal places.
The method shown in Figure 40b can be used as an alternative way of specifying tolerances.
6.9.3 Tolerancing of individual linear dimensions
The method shown in Figure 85 is recommended where it is required to tolerance indi-
Dimensioning
andThis
tolerancing
size specifies both the limits of the size of the6. Dimensioning of technical
19
vidual linear
dimensions.
method of
directly
drawin
dimension, the tolerance being the difference between the limits of the size.
32,15
31,80
nce by
32
+0,15
-0,20
f size
The larger limit of the size is placed
above the smaller limit, and both are given to the
a) places.
same number of decimal
b)
Figure 40 – Linear dimension tolerance by directly specifying limits of size
6.9.4 Tolerancing of individual angular dimensions
The
methods
shown41
in Figure
86used
may be
to tolerance
individual
angular
dimensions.
The methods
shown
in Figure
may be
to used
tolerance
individual
angular
dimensions.
Figure 86: Tolerancing
30 30'
30 0'
(a)
(b)
a)
0
30,5 ± 0,1
90 ± 0 30'
angular dimensions
(c)
b)
c)
Figure 41 – Tolerancing angular dimensions
6.10 Summary
1.13 Interpretations
of limits
ofparts
size
forstandards
a feature-of-size
This chapter has covered
those
of the
that deal with dimensioning and
tolerancing which are likely to be of use to Design and Technology teachers and their
Limits of size for an individual feature-of-size shall be interpreted according to the principles and rules
students in schools and colleges. The key points are as follows.
defined in BS ISO 8015, BS EN ISO 14660-1 and BS EN ISO 14660-2.
A feature-of-size
may consist of two parallel plane surfaces, a cylindrical surface or a spherical
BIP 2155
File name: 2008-01133_40b.e
] The
general
principles
dimensioning
as set out in may
BS 8888:2006
should
always
surface, in each
case
defined
with a of
linear
size. A feature-of-size
also consist
of two
plane surfaces
at an angle to each
other (aifwedge)
a conical surface,
in each
defined
with an angular
be followed
effectiveorcommunication
between
thecase
designer,
manufacturer
and size.
BS ISO 8015
states
that
limits
of
size
control
only
the
actual
local
sizes
(two-point
measurements)
end user is to be established and maintained.
of a feature-of-size and not its deviations of form (e.g. the roundness and straightness deviations of a
] Functional dimensions are those that directly affect the function of the product.
cylindrical feature, or the flatness deviations of two parallel plane surfaces). Form deviations may be
] All dimensions except auxiliary dimensions are subject to tolerancing.
controlled by individually
specified geometrical tolerances, general geometrical tolerances or through
] envelope
The decimal
marker is represented
by a comma
not a point.
the use of the
requirement
(where the maximum
material
limit of size defines an envelope of
perfect form]forGroups
the relevant
surfaces;
seeleft
BS and
ISO right
8015).
of numerals
to the
of the decimal marker should be divided
BS ISO 8015
defines
the
principle
of
independency,
according
to which
specified
up into groups of three, counting from the decimal
marker,
and aeach
full space,
notdimensional
a
and geometrical requirement on a drawing is met independently, unless a particular relationship is
comma, left between them.
specified. A relationship may be specified through the use of the envelope requirement or material
condition modifiers maximum material condition (MMC) or least material condition (LMC).
Where no relationship is specified, any geometrical tolerance applied to the feature-of-size applies
regardless of feature size, and the two requirements shall be treated as unrelated, as shown in Figure 42.
Relevant standards
Title
The limits of size do not control the form, orientation, or the spatial relationship between, individual
Technical drawings — Dimensioning and
features-of-size.BS EN ISO 1660
Consequently, if a particular relationship
of size and
form, or size and location, or size and
tolerancing
of profiles
orientation is required, it needs to be specified.
BS ISO 129-1
Technical drawings — Indication of dimensions
and tolerances — Part 1: General principles
BS 8888:2008
BritiSh Standard
20
The Essential Guide to Technical Product Specification: Engineering Drawing
25,0
24,9
Figure 3 Permissible interpretations when no form control is given on the drawing
a) drawing presentation
a
b
c
NOTE There is no form control (i.e. over roundness, straightness or cylindricity). Measurements a, b and c may
lie between 25.0 mm and 24.9 mm, meeting the drawing requirement using two-point measurement only.
b) Permissible interpretation: straightness unconstrained
Maximum size
5,0
2
Maximum roundness
deviation (resulting
from a lobed form)
NOTE For any cross-section of the cylinder, there is no roundness control.
c) Permissible interpretation: roundness unconstrained
Figure 42 – Permissible interpretations when no form control is given on the drawing
15.1.2 Limits of size with mutual dependency of size and form
COMMENTARY AND RECOMMENDATIONS ON 15.1.2
1.13.1 Limits of size with mutual
dependency
of size
and
form
Some national
standards apply,
or have
applied,
the Envelope
Requirement to all features-of-size by default. As the Envelope
Requirement
the default,
they have
not
used a symbol by
to
Some national standards apply, or have
applied, has
the been
envelope
requirement
to all
features-of-size
indicate this requirement; rather they use a note to indicate when this
default. As the envelope requirement
has been the default, they have not used a symbol to indicate this
is not required. This system of tolerancing is sometimes described as the
requirement; rather they use a note Principle
to indicate
when this is or
notthe
required.
Thisofsystem
of tolerancing
of Dependency,
application
the Taylor
Principle. is
sometimes described as the principle
of dependency,
or the
theEnvelope
Taylor principle.
Standards
which apply,
or application
have applied,ofthe
Requirement by
Standards which apply, or have default
applied,
the envelope requirement by default include:
include:
ASME Y14.5 (the requirement that there is an envelope of perfect
form corresponding to the Maximum Material Size of the feature is
The requirement that there shall be an envelope
perfect
defined asofRule
#1). form corresponding to the maximum
ASME Y14.5
material size of the feature is defined asBS
Rule
308#1).
(the Principle of Dependency was taken as the default
option under BS 308, although the option of working to the
Principle of Independency was included, through the use of
The principle of dependency was taken as
the
optionI indication):
under BS 308, although the option of working
the
BSdefault
308 triangle
BS 308
I
8888
to the principle of independency was included, through the use of theBS BS
308 triangle I indication.
BS 8888 prior to the 2004 revision (the Principle of Dependency was
I
taken
option under BS 8888:2000 and BS 8888:2002,
BS as
8888the default
although the option of working to the Principle of Independency was
included, through the use of the BS 8888 triangle I indication).
16 • © BSI 2008
21
Dimensioning and tolerancing of size
BS 8888
Prior to the 2004 revision; the principle of dependency was taken as the default option under
BS 8888:2000 and BS 8888:2002, although the option of working to the principle of independency
was included, through the use of the BS 8888 triangle I indication.
BS 8888:2004 and BS 8888:2006
the principle of dependency could be explicitly invoked through the use of the BS 8888 triangle D indication.
BS 8888
D
As the interaction between the envelope requirement and individual geometrical tolerances is not
always fully defined within the ISO system, and as the application of the envelope requirement by
default to all features-of-size is not formally supported within the ISO system, the use of the principle of
dependency is no longer recommended.
1.14 Datum surfaces and functional requirements
Functional dimensions shall be expressed directly on the drawing, as shown in Figure 1. The application
of this principle will result in the selection of reference features on the basis of the function of the
product and the method of locating it in any assembly of which it may form a part.
If any reference feature other than one based on the function of the product is used, finer tolerances
will be necessary to meet the functional requirement, which in turn will increase the cost of producing
the product, as shown in Figure 43 on page 22.
1.15 Relevant standards
BS EN ISO 1660, Technical drawings — Dimensioning and tolerancing of profiles
BS ISO 129-1, Technical drawings — Indication of dimensions and tolerances — Part 1:
General principles
BS ISO 3040, Technical drawings — Dimensioning and tolerancing — Cones
BS ISO 10579, Technical drawings — Dimensioning and tolerancing — Non-rigid parts
BS ISO 406, Technical drawings — Tolerancing of linear and angular dimensions
BS EN 22768-1, General tolerances — Part 1: Tolerances for linear and angular dimensions without
individual tolerance indications
BS 4235-1, Specification for metric keys and keyways — Part 1: Parallel and taper keys
BS 4235-2, Specification for metric keys and keyways — Part 2: Woodruff keys and keyways
BS ISO 8015, Technical drawings — Fundamental tolerancing principle
BS EN ISO 14660-1, Geometrical Product Specifications (GPS) — Geometrical features — Part 1:
General terms and definitions
BS EN ISO 14660-2, Geometrical Product Specifications (GPS) — Geometrical features — Part 2:
Extracted median line of a cylinder and a cone, extracted median surface, local size of an extracted
feature
PP 8888-2, Engineering drawing practice: a guide for further and higher education to BS 8888:2006,
Technical product specification (TPS)
A
22
The Essential Guide to Technical Product Specification: Engineering Drawing
Description
Drawing
1
2
12,00
11,92
Date:
15/06/2009
Approval
of issue
6,05
6,00
5,5
5,0
NOTE: One direct dimension with
a tolerance of 0.05 mm is needed
to satisfy the condition shown in a).
A nominal flange thickness of 5 mm
has been assumed. This value is
non-functional and can have
BIPany
2155
large tolerance.
Modifications:
File name: 2008-01133_43a.eps
correct functional reference surface
d) Item 2 dimensioned from a nonfunctional reference surface
File name: 2008-01133_43b.eps
BSI/PM: Jenny Cranwell
Date: 15/06/2009
BIP 2155
11,03
11,00
5,00
4,98
NOTE: Tolerances have had to
be reduced; two dimensions with
tolerances of, say, 0.02 mm for the
flange and 0.03 mm are now needed
to satisfy the condition shown in a).
incorrect non-functional reference surface
Figure 43 – Effect on tolerances by changing datum surfaces
from those determined by functional requirements
BIP 2155
Date: 15/06/2009
Modifications:
c) Item 2 dimensioned from a
functional reference surface
18,00
17,97
b) Detail of head of item 1 showing
given limits of size, with a tolerance
of 0.03 mm
Modifications:
3
BSI/PM: Jenny Cranwell
Approval of issue
a) Assembly drawing showing a
given functional requirement, namely
the limits of height of the top face
of item 1 above the top face of
item 3, with a tolerance of 0.08 mm
File name: 2008-01133_43c.eps