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INTERNATIONAL
STANDARD
ISO
First edition 1989-11-
General tolerantes -
Part 1:
Tolerantes for linear and angular dimensions without
individual tolerante indications
Tolhrances ghhales - Partie I : Tolhrances pour dimensions fin4aires et angulaires non affectdes de tolhrances individuelles
Reference number ISO 2768-1 : 1989 (E)
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ISO 2768-1 : 1989 (EI
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO member bedies). The work of preparing International Standards is normally carried out through ISO technical committees. Esch 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, govern- mental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) 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 ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting.
International Standard Limits and fits.
ISO 2768- 1 was prepared (^) bY Technical Committee ISO/TC 3,
This first edition of ISO 2768-1, together with ISO 2768-2 : 1989, cancel and replace ISO 2768 : 1973.
ISO 2768 consists of the following Parts, under the general title General tolerantes:
- Part 7 : Tolerantes tolerante indica tions
- Part ca tions
2: Geome trical tolerantes for fea tures without individual tolerante indi-
for linear and angular dimensions withou t individual
Annex A of this part of ISO 2768 is for information only.
0 ISO 1989 All rights reserved. No patt of this pubiication may be reproduced or utilized in any form or by any means, electronie or mechanical, including photocopying and microfilm, without Permission in writing from the publisher. International Organization for Standardization Case postale 56 l CH-121 1 Geneve 20 l Switzerland Printed in Switzerland
ii
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INTERNATIONAL STANDARD ISO2768-1^ : 1989 (EI
General tolerantes -
Part 1 I
Tolerantes for linear and angular dimensions without individual _
tolerante indications
1 Scope
This part of ISO 2768 is intended to simplify drawing indica- tions and it specifies general tolerantes for linear and angular dimensions without individual tolerante indications in four tol- erance classes.
NOTE 1 - The concepts behind the general tolerancing of linear and angular dimensions are described in annex A.
lt applies to the dimensions of Parts that are produced by metal removal or Parts that are formed from sheet metal.
NOTES
2 These tolerantes may be suitable for use with materials other than metal.
3 Parallel International Standards exist or are planned, e.g. see ISO 80621) for castings.
This patt of ISO 2768 only applies for the following dimensions which do not have an individual tolerante indication :
a) linear dimensions (e-g. extemal sizes, internal sizes, step sizes, diameters, radii, distances, extemal radii and chamfer heights for broken edges);
b) angular dimensions, including angular dimensions usually not indicated, e.g. right angles No), unless ref- erence to ISO 2768-2 is made, or angles of uniform poly- gons;
c) linear and angular dimensions produced by machining assembled Parts.
It does not apply for the following dimensions :
a) linear and angular dimensions which are covered by reference to other Standards on general tolerantes;
b) auxiliary dimensions indicated in brackets;
c) theoretically exact dimensions indicated in rectangular f rames.
2 General
When selecting the tolerante class, the respective customary Workshop accuracy has to be taken into consideration. If smal- ler tolerantes are required or larger tolerantes are permissible and more economical for any individual feature, such toleran- ces should be indicated adjacent to the relevant nominal dimen- sion(s).
General tolerantes for linear and angular dimensions apply’ when drawings or associated specifications refer to this patt of ISO 2768 in accordance with clauses 4 and 5. If there are gen- eral toierances for other processes, as specified in other lnter- national Standards, reference shall be made to them on the drawings or associated specifications. For a dimension between an unfinished and a finished surface, e.g. of cast or forged Patts, for which no individual tolerante is directly indi- cated, the larger of the two general tolerantes in question applies, e.g. for castings, see ISO 80621).
3 Normative references
The following Standards contain provisions which, through reference in this text, constitute provisions of this patt of ISO 2768. At the time of publication, the editions indicated were valid. All Standards are subject to revision, and Parties to agreements based on this patt of ISO 2768 are encouraged to investigate the possibility of applying the most recent editions of the Standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 2768-2 : 1909, General tolerantes - Part 2: Geometrical tolerantes for features without individual tolerante indications.
ISO 8015 : 1985, Technical drawings - Fundamental toleran- cing principle.
4 General tolerantes
4.1 Linear dimensions
General tolerantes for linear dimensions are given in tables 1 and 2.
- ISO 8062 : 1984, Castings - System of dimensional tolerantes. Licensed to PTI/PIERRE GROSSMANN ISO Store order #: 686972/Downloaded: 2005-08-
ISO27684 :1989 (EI
Annex A
(informative)
Concepts behind general tolerancing of linear and angular dimensions
A.1 General tolerantes should be indicated on the drawing by reference to this part of ISO 2768 in accordance with clause 5.
The values of general tolerantes correspond to tolerante classes of customary Workshop accuracy, the appropriate tolerante class being selected and indicated on the drawing ac- cording to the requirement for the components.
A.2 Above certain tolerante values, there is usually no gain in manufacturing economy by enlarging the tolerante. For example, a feature having a 35 mm diameter could be manufac- tured to a high level of conformance in a Workshop with “customary medium accuracy”. Specifying a tolerante of -t 1 mm would be of no benefit in this particular Workshop, as the general tolerante values of +0,3 mm would be quite adequate.
However, if, for functional reasons, a feature requires a smaller tolerante value than the “general tolerantes”, then that feature should have the smaller tolerante indicated individually adja- cent to the dimension defining its size or angle. This type of tolerante falls outside the scope of general tolerantes.
In cases where the function of a feature allows a tolerante equal to or larger than the general tolerante values, these should not be indicated adjacent to the dimension but should be stated on the drawing as described in clause 5. This type of tolerante allows full use of the concept of general tolerancing.
There will be “exceptions to the rule” where the function of the feature allows a larger tolerante than the general tolerantes, and the larger tolerante will provide manufacturing economy. In these special cases, the larger tolerante should be indicated individually adjacent to the dimension for the particular feature, e.g. the depth of blind holes drilled at assembly.
A.3 Using general tolerantes leads to the following advan- tages :
a) drawings are easier to read and thus communication is made more effective to the user of the drawing;
b) the design draughtsman saves time by avoiding de- tailed tolerante calculations as it is sufficient only to know that the function allows a tolerante greater than or equal to the general tolerante;
c) the drawing readily indicates which feature tan be pro- duced by normal process capability, which also assists quality engineering by reducing inspection levels;
d) those dimensions remaining, which have individually in- dicated tolerantes, will, for the most patt, be those control- ling features for which the function requires relatively small tolerantes and which therefore may require special effort in the production - this will be helpful for production plan- ning and will assist quality control Services in their analysis of inspection requirements;
e) purchase and sub-contract supply engineers tan negotiate orders more readily since the “customary Workshop accuracy” is known before the contract is placed; this also avoids arguments on delivery between the buyer and the supplier, since in this respect the drawing is com- plete.
These advantages are fully obtained only when there is sufficient reliability that the general tolerantes will not be exceeded, i.e. when the customary Workshop accuracy of the particular Workshop is equal to or finer than the general tolerantes indicated in the drawing.
The Workshop should, therefore
- find out by measurements what its customary Workshop accuracy is;
- (^) accept only those drawings having general tolerantes equal to or greater than its customary Workshop accuracy;
- (^) check by sampling that its customary Workshop accu- racy does not deteriorate.
Relying on undefined “good workmanship” with all its uncer- tainties and misunderstandings is no longer necessary with the concept of general geometrical tolerantes. The general geometrical tolerantes define the required accuracy of “good workmanship”.
A.4 The tolerante the function allows is often greater than the general tolerante. The function of the patt is, therefore, not always impaired when the general tolerante is (occasionally) exceeded at any feature of the workpiece. Exceeding the general tolerante should lead to a rejection of the workpiece only if the function is impaired.
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ISO 2768-1 : 1989 (EI
UDC 621.753.1 : 744.
Descriptors : fundamental tolerantes, dimensional tolerantes, angular toleyances.
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