Introduction

The preparation of a vocabulary of gears may be conceived in many different ways, depending on the aim; in its most simplified form, the vocabulary may have the sole purpose of fixing the terminology, which sometimes varies from one workshop to another. In other words, it may consist of a simple list of recommended terms, possibly completed by equivalent terms in other languages, but without definitions, on the assumption that these are already familiar to the people dealing with gears. On the other hand, the vocabulary may be a proper document of instruction, containing both the definition of each term and all useful comments to make it readily understandable to young people and to enable them to grasp the various mathematical and practical consequences which may result in connection with the other definitions.

Since we are dealing with international standardization, it seems essential to enable people who deal with gears to understand one another, without error or ambiguity, by providing them with standard terms in each language which have exactly the same meaning from one country to another.

This part of ISO 1122 must not therefore be regarded as aiming directly at teaching, which would require longer explanations, nor as intended specifically for workshop technicians, who would doubtless prefer shortened and perhaps less rigorous definitions which could easily be assimilated in the light of their long experience. This part of ISO 1122 has been drawn up for general use in the sense of a dictionary which may confidently be consulted in case of doubt or disagreement.

For this reason, this part of ISO 1122 gives a geometrical definition which is as rigorous as possible for each term, since this is an indispensable factor in eliminating uncertainty in the interpretation of difficult passages, especially for dealings between countries where different languages are used.

While certain definitions may therefore seem somewhat abstract in character, the work was nevertheless carried out taking account solely of practical needs, deliberately leaving out all purely theoretical and historical considerations. (For example, only ordinary gears with constant ratio are considered, to the exclusion of elliptical or other types of gears, and no reference is made to operating hyperboloids, which have their place in kinematic theories but are not actually used in the study, cutting or use of gear wheels.)

For the same reason, when two equivalent definitions would be equally possible for the same term, but one is a consequence of the other, only the more general definition has been retained as a basic definition even if, in some cases, it would have been more convenient to use the other. (For example, the module may be defined in terms of the pitch or of the diameter and the number of teeth; here, the first definition, which is more general and is applicable even in the case of the rack, must be considered to be the basic definition).

Comparison of this proposal with the standards and proposals which were used as a starting point shows a great similarity of content; this similarity is clearly imposed by gear engineering itself, which is the same in all countries.

As regards form, the following should be noted:

— the addition of certain terms which did not exist in older standards (e.g. constant chord);
— the elimination of some other terms, which are of either secondary or no interest in practice and which actually belong, to a vocabulary of geometrical of kinematic sciences rather than a vocabulary of gears, and which have already been adequately defined in this respect;
— lastly, certain French terms did not have corresponding terms in English; in the English version, these terms appear as translations of the French terms and are given in square brackets.

The studies carried on in the field of gears (calculation, precision, codes of practice, ...) since the publication of the first edition of ISO 1122-1, have shown the necessity of a revision of that edition.

Besides the deletion of some non-used terms in practice and some improvements brought to the English terminology (particularly for the terms in square brackets) these studies have shown the necessity of:

— dividing definitions which covered similar concepts in the first edition (opposite terms or terms of the same family);
— adding some terms for which the geometrical definition was missing.

BS ISO 1122-1:1998

Vocabulary of gear terms - Definitions related to geometry

Current, Under Review

Published:

15 Oct 1998