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IS0
INTERNATIONAL STANDARD
2768-2 First edition 1989-11-15
General
tolerances
Part 2: Geometrical tolerances tolerance indications Tolkrances
for features
without
individual
g8ntGrales -
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Partie 2: Tolhances individuelles
g6omhtriques
pour
Sments
non affect&
de tokrances
Reference number IS0 2768-2 : 1959 (E)
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2768-2
: 1989 (EI
Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IECI on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Limits
Standard
IS0 2768-2 was prepared by Technical
Committee
ISO/TC
3,
and fits.
This first edition of IS0 2768-2, together with IS0 2758-1 : 1969, cancel and replace IS0 2759 : 1973. IS0 2768 consists of the following
Part tolerance
I: Tolerances indications
Fart 2: cations
Geometrical
for
parts, under the general title Genera/ tolerances: linear
tolerances
and
angular
for features
dimensions
without
Annexes A and B of this part of IS0 2768 are for information
0
IS0
without
individual
individual
tolerance
indi-
only.
1999
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56 l CH-1211 Geneve 20 l Switzerland Printed in Switzerland
ii
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IS0
IS0 2768-2 : 1989 (El
Introduction All features on component parts always have a size and a geometrical shape. For the deviation of size and for the deviations of the geometrical characteristics (form, orientation and location) the function of the part requires limitations which, when exceeded, impair this function. The tolerancing on the drawing should be complete to ensure that the elements of size and geometry of all features are controlled, i.e. nothing shall be implied or left to judgement in the workshop or in the inspection department. The use of general tolerances for size and geometry simplifies the task of ensuring that this prerequisite is met.
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iii
INTERNATIONAL
General
tolerances
Part 2: Geometrical tolerances tolerance indications
1
IS0 2758-2 : 1989 (E)
STANDARD
-
for features without
Scope
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This part of IS0 2768 is intended to simplify drawing indications and specifies general geometrical tolerances to control those features on the drawing which have no respective individual indication. It specifies general geometrical tolerances in three tolerance classes. This part of IS0 2768 mainly applies to features which are produced by removal of material. Its application to features manufactured by other processes is possible; however, special examination is required to ascertain whether the customary workshop accuracy lies within the general geometrical tolerances specified in this part of IS0 2768.
2
individual
IS0 2768. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of IS0 2768 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 1101 : 1983, Technical drawings - Geometrical tolerancing - Tolerancing of form, orientation, location and run-out Generalities, definitions, symbols, indications on drawings. IS0 2768-l : 1989, General tolerances linear and angular dimensions without cations.
- Part 7: Tolerances for individual tolerance indi-
IS0 5459 : 1981, Technical
General
ing -
When selecting the tolerance class, the respective customary workshop accuracy has to be taken into consideration. If smaller geometrical tolerances are required or larger geometrical tolerances are permissible and more economical for any individual feature, such tolerances should be indicated directly in accordance with IS0 1101 (see clause A.2).
General geometrical tolerances apply to all geometrical tolerance characteristics, excluding cylindricity, profile of any line, profile of any surface, angularity, coaxiality, positional tolerances and total run-out.
drawings - Geometrical tolerancand datum-systems for geometrical tolerances.
IS0 8015 : 1995, Technical ing principle.
4 General geometrical tolerances in accordance with this part of IS0 2768 apply when drawings or associated specifications refer to this part of IS0 2768 in accordance with clause 6. They apply to features which do not have respective individual geometrical tolerance indications.
Datums
drawings
-
Fundamental
toleranc-
Definitions
For the purposes of this part of IS0 2768, the definitions for geometrical tolerances given in IS0 1101 and IS0 5459 apply.
5
General
geometrical
tolerances
(see also clause 5.1) 5.1
Tolerances
for single
features
In any event, general geometrical tolerances in accordance with this part of IS0 2768 should be used when the fundamental tolerancing principle in accordance with IS0 8015 is used and indicated on the drawing (see clause 6.11.
5.1.1
3
The general tolerances on straightness and flatness are given in table 1. When a tolerance is selected from table 1, it shall be based, in the case of straightness, on the length of the corresponding line and, in the case of flatness, on the longer lateral length of the surface, or the diameter of the circular surface.
Normative
references
The following standards contain reference in this text, constitute
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provisions which, through provisions of this part of
Straightness
and flatness
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1
2768-2
: 1989 (El
Table 1 -
General tolerances and flatness
on straightness Values in millimetres
Straightness
and flatness tolerances for ranges of nominal lengths
Tolerance class
5.2.3
Perpendicularity
The general tolerances on perpendicularity are given in table 2. The longer of the two sides forming the right angle shall be taken as the datum; if the sides are of equal nominal length, either may be taken as the datum.
Table 2 -
General
tolerances
on perpendicularity
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IS0
Values in millimetres Perpendicularity
K ante class
5.1.2
Circularity
The general tolerance on circularity is equal to the numerical value of the diameter tolerance, but in no case shall it be greater than the respective tolerance value for circular radial run-out given in table 4 (see examples in clause 8.2).
5.1.3
I
Cylindricity
f The cylindricity deviation comprises three components : circularity deviation, straightness deviation and parallelism deviation of opposite generator lines. Each of these components is controlled by its individually indicated or its general tolerance.
0,3
0,4
0.5
K
O,4
‘A6
033
1
L
W-3
1
I,5
2
Symmetry
NOTE - The general tolerances on symmetry apply where at least one of the two features has a median plane, or the axes of the two features are perpendicular to each other. See examples in clause B.5. General
for
related
tolerances
on symmetry Values in millimetres
Symmetry Tolerante class
tolerances for ranges of nominal lengths
over 100 over 300 I up to 300 I up to 1 ooo
up to 100
H
W-3
L
features
over 1 Do0 up to 3 ooo
0,5
K
033 1
1
‘323
1
I,5
2
General 5.2.5
The tolerances specified in 5.2.2 to 5.2.6 apply to all features which are in relation to one another and which have no respective individual indication.
Parallelism
The general tolerance on parallelism is equal to the numerical value of the size tolerance or the flatness/straightness tolerance, whichever is the greater. The longer of the two features shall be taken as the datum; if the features are of equal nominal length, either may be taken as the datum (see clause B.4).
2
over 1 000 up to 3 ooo I
02
5.2.4
Sometimes, e.g. in the case of a fit, the indication of the envelope requirement @ is appropriate.
5.2.2
over 300 up to 1 oao
H
Table 3 2 If, for functional reasons, the cylindricity deviation has to be smaller than the combined effect (see clause B-3) of the general tolerances on circularity, straightness and parallelism, an individual cylindricity tolerance in accordance with IS0 1101 should be indicated for the feature concerned.
5.2.1
up to 300
are not specified.
NOTES
Tolerances
over 100 I
up to loo
I
The general tolerances on symmetry are given in table 3. The longer of the two features shall be taken as the datum; if the features are of equal nominal length, either may be taken as the datum.
General tolerances on cylindricity
5.2
tolerances for ranges of lengths of the shorter side
nominal
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Coaxiality
General tolerances on coaxiality are not specified. NOTE - The deviation in coaxiality may, in an extreme case, be as great as the tolerance value for circular radial run-out given in table 4, since the deviation in radial run-out comprises the deviation in coaxiality and the deviation in circularity. 5.2.6
Circular
run-out
The general tolerances on circular run-out (radial, axial and any surface of revolution) are given in table 4.
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IS0 2766-2 : 1989 (E)
In this case the general tolerances for angular dimensions in accordance with IS0 2766-l do not apply to right angles (W’), which are implied but not indicated, because this part of IS0 2766 specifies general tolerances on perpendicularity.
For general tolerances on circular run-out, the bearing surfaces shall be taken as the datum if they are designated as such. Otherwise, for circular radial run-out, the longer of the two features shall be taken as the datum; if the features are of equal nominal length, either may be taken as the datum. Table
4 -
General
tolerances
on circular
run-out
Values in millimetres Tolerance
class
Circular
run-out
tolerances
EXAMPLE
H
I
I
K
I
0.2
I
I
L
I
0.5
I
6
Indications
or1
on drawings
6.1
If general tolerances in accordance with this part of IS0 2766 shall apply in conjunction with the general tolerances in accordance with IS0 2766-1, the following information shall be indicated in or near the title block:
a) “IS0 2768”; b)
6.2 If the general dimensional tolerances (tolerance class m) shall not apply, the respective letter shall be omitted from the designation to be indicated on the drawing :
IS0
2768-K
6.3
In cases where the envelope requirement @ also applies to all single features of size l), the designation “E” shall be added to the general designation specified in 6.1 : EXAMPLE IS0 2768-mK-E
NOTE - The envelope requirement @ cannot apply to features with individually indicated straightness tolerances which are greater than their size tolerances, e.g. stock material.
the tolerance class in accordance with IS0 2766-l ;
c) the tolerance IS0 2766.
class in accordance
EXAMPLE IS0 2768-mk
with
this part of
7
Rejection
Unless otherwise stated, workpieces exceeding the general geometrical tolerance shall not lead to automatic rejection provided that the ability of the workpiece to function is not impaired (see clause A.4).
1) For the purposes of this part of IS0 2768, a single feature of size comprises a cylindrical surface or two parallel plane surfaces. --``,`,```,``,`,```,``,`,```-`-`,`,`,`,`---
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3
IS0
2768-2 : 1989 (El
Annex
A
(informative)
Concepts
behind
general
tolerancing
of geometrical
characteristics
b) the design draughtsman saves time by avoiding detailed tolerance calculations as it is sufficient only to know that the function allows a tolerance greater than or equal to the general tolerance;
The values of general tolerances correspond to grades of customary workshop accuracy, the appropriate tolerance class being selected and indicated on the drawing.
cl the drawing readily indicates which features can be produced by normal process capability, which also assists quality engineering by reducing inspection levels;
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A.1 General tolerances should be indicated on the drawing by reference to this part of IS0 2766 in accordance with clause 6.
d) those features remaining, which have individually indicated geometrical tolerances, will, for the most part, be those controlling features for which the function requires relatively small tolerances and which therefore may cause special effort in the production - this will be helpful for production planning and will assist quality control services in their analysis of inspection requirements;
A.2
Above a certain tolerance value, which corresponds to the customary workshop accuracy, there is usually no gain in manufacturing economy by enlarging the tolerance. In any event, workshop machinery and the usual workmanship normally do not manufacture features with greater deviations. For example, a feature of 25 mm I!I 0,l mm diameter by 66 mm long manufactured in a workshop with a customary accuracy equal to or finer than IS0 276%mH contains the geometrical deviations well within 0,l mm for circularity, 0,l mm for straightness of surface elements, and 0,l mm for circular radial run-out (the values given have been taken from this part of IS0 2766). Specifying tolerances would be of no benefit in this particular workshop. However, if, for functional reasons, a feature requires a smaller tolerance value than the “general tolerances”, then that feature should have the smaller tolerance indicated individually adjacent to the particular feature. This type of tolerance falls outside the scope of general tolerances.
e) purchase and sub-contract tiate orders more readily since curacy” is known before the avoids arguments on delivery supplier, since in this respect
These advantages are fully obtained only when there is sufficient reliability that the general tolerances will not be exceeded, i.e. when the customary workshop accuracy of the particular workshop is equal to or finer than the general tolerances indicated in the drawing. The workshop
should, therefore,
find out by measurements shop accuracy is ;
In cases where the function of a feature allows a geometrical tolerance equal to or larger than the general tolerance values, this should not be individually indicated, but should be stated on the drawing as described in clause 6. This type of tolerance allows full use of the concept of general geometrical tolerancing. There will be “exceptions to the rule” where the function allows a larger tolerance than the general tolerances, and the larger tolerance will provide a gain in manufacturing economy. In these special cases, the larger geometrical tolerance should be indicated individually adjacent to the particular feature, e.g. the circularity tolerance of a large and thin ring.
supply engineers can negothe “customary workshop accontract is placed; this also between the buyer and the the drawing is complete.
what its customary
accept only those drawings having general tolerances equal to or greater than its customary workshop accuracy; check by sampling that its customary curacy does not deteriorate.
Using general geometrical following advantages :
4
leads to
the
a) drawings are easier to read and thus communication made more effective to the user of the drawing;
is
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tolerances
workshop
ac-
Relying on undefined “good workmanship” with all its uncertainties and misunderstandings is no longer necessary with the concept of general geometrical tolerances. The general geometrical tolerances define the required accuracy of “good workmanship”.
A.4 A.3
work-
The tolerance the function allows is often greater than the general tolerance. The function of the part is, therefore, not always impaired when the general tolerance is (occasionally) exceeded at any feature of the workpiece. Exceeding the general tolerance should lead to a rejection of the workpiece only if the function is impaired.
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IS0 2768-2 : 1989 (E)
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Annex B (informative) Further
information
(see clause 5)
general geometrical tolerances may be used even if the features are everywhere at their maximum material size (see figure B.l).
According to the principle of independency (see IS0 8015). general geometrical tolerances apply independently of the actual local size of the workpiece features. Accordingly, the
If the envelope requirement @ is individually indicated adjacent to the feature or generally to all features of size as described in clause 6, this requirement should also be complied with.
B.l
General
geometrical
tolerances
Dimensions
in millimetres
t y I
,-Maximum
250
IS0 2768-mH
circularity deviation from a lobed form) straightness
LMaximum
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8015
-I
Maximum
Principle
IS0
General tolerances
limit of size -Maximum Maximum (resulting
Figure B.l -
Tolerancing
of independency;
maximum
permissible
deviation deviation-.,
limit of size
deviations
on the same feature
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5
IS0
2768-2 : 1989 (E)
B.2
Circularity
EXAMPLE
(see 5.1.2)
-
Examples
B.3
Cylindricity
(see note 2 in 5.1.3)
The combined effect of the general tolerances of circularity, straightness and parallelism is, for geometrical reasons, smaller than the sum of the three tolerances since there is also a certain limitation by the size tolerance. However, for the sake of simplicity, in order to decide whether the envelope requirement E or an individual cylindricity tolerance is to be indicated, the sum of the three tolerances can be taken into account.
1 (see figure 8.2)
The permissible deviation of the diameter is indicated directly on the drawing; the general tolerance on circularity is equal to the numerical value of the diameter tolerance.
0
EXAMPLE 2 (see figure 8.21
B.4
The general tolerances in accordance with the indication IS0 275B-mK apply. The permissible deviations for the diameter of 25 mm are +0,2 mm. These deviations lead to the numerical value of 0,4 mm which is greater than the value of 0,2 mm given in table 4; the value of 0,2 mm, therefore, applies for the circularity tolerance.
Parallelism
(see 5.2.2)
Depending on the shapes of the deviations of the features, the parallelism deviation is limited by the numerical value of the size tolerance (see figure B.3) or by the numerical value of the straightness or flatness tolerance (see figure B.4).
Values
Example
Indication
on the drawing
Circularity
tolerance
in millimetres
zone
1
IS0 2768-K
2
IS0 276%mK
Figure
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Figure
Dimensional
B.3 -
B.2 -
Examples
of general
tolerances
-Straightness
tolerance
Parallelism deviation equal to the numerical value of the size tolerance
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on circularity
Figure
tolerance
B.4 - Parallebsm deviation equal to the numerical value of the straightness tolerance
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IS0 2758-2 : 1989 (E)
Symmetry
(see 5.2.4) -
Examples
a)
Datum
: longer
feature
(/,I
b)
Datum
: longer
feature
(I,)
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8.5
I
I
i ,
1
fi
c)
Datum
it’-‘-l I Figure 8.5 -
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Examples
feature
(/,I
g& ‘1
u
d)
: longer
Datum
of general tolerances
12
-I : longer
feature
on symmetry
(I,)
(datums specified in accordance with 5.2.4)
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IS0
2768-2:1989
B.6
Example
Indication
(EI
of a drawing
on the drawing
Dimensions in millimetres
LSa,.
245' 83H12(+$')
Tolerancing IS0 8015 General tolerances IS0 2768-mH
Interpretation
t
-
NOTES 1 The tolerances shown in chain thin double-dashed lines (boxes and circles) are general tolerances. These tolerance values would be automatically achieved by machining in a workshop with a customary accuracy equal to or finer than IS0 2768-mH and would not normally require to be inspected. 2 As some tolerances also limit the deviations of other characteristics of the same feature, straightness deviations, not all general tolerances are shown in the interpretation above.
Figure
UDC
621.753.1
Descriptors
B.6 -
Example
of general
tolerances
e.g. the perpendicularity
tolerance also limits the
on a drawing
: 744.4
: fundamental
tolerances,
machining tolerances,
geometrical
tolerances.
Price based on 8 pages
8
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