Technical Drawing. Preparation of manufacturing documents. Subject module. Independency principle, envelope requirement and two-point size

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1 Technical Drawing Preparation of manufacturing documents Subject module Independency principle, envelope requirement and two-point size EDITION SWISSMEM

2 Impressum Published by: Title: Edition Swissmem Technical Drawing Preparation of manufacturing documents Subject module «Independency principle, Envelope requirement and two-point size» Edition: Second edition 2016 Copyright Edition Swissmem, Zürich and Winterthur Order code: XXFMTO 1S e ISBN number: Project management: Joachim Pérez, Swissmem Vocational Training, CH-8400 Winterthur Author: Willi Tschudi, CH-8355 Aadorf Layout and drawings: Daniel Baur, Swissmem Vocational Training, CH-8400 Winterthur Technical editor: Prof. Dr.-Ing Volker Läpple, Steinbeis-Beratungszentrum Konstruktion, Werkstoffe und Normung, D Schorndorf Printing: Printed in Switzerland Sources: Purchase from: Copyright SNV Swiss Association for Standardization, DIN e.v., the object designated sources Swissmem Vocational Training Brühlbergstrasse 4 CH-8400 Winterthur Telefon Fax vertrieb.berufsbildung@swissmem.ch All rights reserved. The work and all its parts arte protected by copyright Any use other than as permitted by law requires previous written permission from the publisher.

3 Independency principle, envelope requirement and two-point size 3 Table of Contents/Legend Table of Contents: 1. Introduction Drawing indication independency principle Notes Drawing indication envelope requirement 5 2. Explanation of two-point size Determination of ISO default specification operators for size Testing basis envelope requirement vs. two-point size Consequences of using two-point size Examples of drawing notations No indication Indication ISO Envelope requirement Partial indication of the envelope requirement Examples of drawings Exercises Exercise «Intermediate gear» Exercise «Scanning device» 22 Legend: Useful tips Solve the exercise by appropriate means.

4 4 Independency principle, envelope requirement and two-point size 1. Introduction For engineering/technical drawings prepared on the basis of global ISO GPS Standards, the rules, concepts and principles in ISO 8015:2011 apply by default, unless agreed otherwise. One of these fundamental rules is the independency principle (also known as the principle of independency). The independency principle states that specifications, e.g. dimension, shape and location tolerances, are fully independent of each other, and must therefore be checked and fulfilled independently of one another. Also, with the introduction of ISO , the standard DIN 7167 ( envelope requirement ), widely used in Germany and Switzerland, was withdrawn. The envelope requirement must therefore now be explicitly indicated on all drawings in which it applies. The envelope requirement (DIN 7167) was applicable in Germany from 1987 to 2011 even when the standard was not indicated on a drawing. 1.1 Drawing indication independency principle (ISO 8015) Each GPS specification applies only to the size given. Shape deviations are limited e.g. by a general tolerance, but are in no way dependent on the size tolerance. Each size, shape and location tolerance is tested separately. Example: ø30h6 ok ok ok ok ok 1.2 Notes As a rule, the envelope requirement is used for clearance fits and sometimes for transition fits, but not for interference fits. With interference fits, the material is knowingly deformed. Achieving the envelope before force fitting requires more manufacturing effort, but is scarcely useful as regards function. Features of size: Circles, cylinders, spheres, two parallel opposite edges or surfaces, which must be able to be measured between two points.

5 Independency principle, envelope requirement and two-point size 5 1. Introduction 1.3 Drawing indication envelope requirement (ISO E ) - (DIN 7167 withdrawn) The size tolerance limits the shape and parallelism of opposite lines. Not only the size requirement must be met, but also all the geometry must be within the theoretical tolerance envelope. The envelope requirement is only used with respect to features of size. These are: circles, cylinders, spheres, two parallel opposite edges or surfaces, which must be able to be measured between two points. On the basis of shape and location tolerances, the envelope requirement limits the straightness, flatness, roundness, cylindrical shape, as well as parallelism related to planes and edge lines. Deviations in shape and location tolerances must be indicated separately. Envelope (ø30,0) ø30h6 E finished workpiece Permissible form deviation The idea behind the independency principle is to reduce manufacturing costs. Only where really necessary should increased effort be made, and individual features of size indicated by the modifier E Using the independency principle, every tolerance is tested individually. Testing of tolerances using the envelope requirement requires e.g. a ring gauge, a plug gauge or a coordinate measuring machine (CMM) with corresponding evaluation software. Maintaining the envelope requires increased manufacturing effort.

6 6 Independency principle, envelope requirement and two-point size Notes

7 Independency principle, envelope requirement and two-point size 7 2. Explanation of two-point size

8 8 Independency principle, envelope requirement and two-point size 2. Explanation of two-point size The publication of ISO (in 2010) specified for the first time, in conjunction with ISO , how a two-point size is defined on a workpiece with deviations from the ideal geometric form in cases where no separate agreement is made. 2.1 Determination of ISO default specification operators for size In cases where in the technical specification (e.g. engineering drawing) no separate agreement is made, then according to ISO the two-point size is assumed as a matter of principle to be agreed to features of size (with evaluation according to ISO ). Example: Specification (engineering drawing) ø20±0,1 Responsible dept. Technical reference Prepared by: Approved by: Document type Document status Title, additional title Rev. Issue date Lang. Sheet Interpretation according to ISO The local distance between two opposite points taken on a feature of size (e.g. between two parallel opposite planes or cylinder diameter) may not be less than the lower limit of size and may not exceed the upper limit of size. d d d Measurement/proof of conformity According to ISO the value (19,9 mm d 20,1) mm must be complied with between two opposite points at all cross sections. Examples of measuring equipment (pay attention to the measurement uncertainty): calliper gauge micrometer

9 Independency principle, envelope requirement and two-point size 9 2. Explanation of two-point size 2.2 Testing basis envelope requirement vs. two-point size Specification (Engineering drawing) ø20±0,1 E ø20±0,1 Responsible dept. Technical reference Prepared by: Approved by: Responsible dept. Technical reference Prepared by: Approved by: Document type Document status Document type Document status Title, additional title Title, additional title Rev. Issue date Lang. Sheet Rev. Issue date Lang. Sheet Testing using ring gauge (GO) ø20 ± 0,1 E envelope requirement agreed Testing using two-point size ø20 ± 0,1 two-point size agreed Ring gauge ø20,1 mm

10 10 Independency principle, envelope requirement and two-point size 2. Explanation of two-point size 2.3 Consequences of using two-point size The two-point size defines according to ISO the distance between two opposite points. Therefore, the two-point size does not test the shape. Unless additional requirements are set, e.g. general tolerances or indications in the drawing using the symbols in ISO 1101, there are no limits on deviations of shape (straightness, flatness, roundness, cylindricity). Where, for functionality reasons (e.g. to ensure assembly of a clearance fit), a limit must be placed on deviations of shape, agreement must be reached on the use of either the envelope requirement or geometric tolerances. d 1 d 2 = d 1 The two-point size does not test, among other things, for deviations of shape The calliper gauge shown is representative for the measurement of the two-point size. Depending on the specified tolerance, it may be necessary to use other measuring equipment with other measurement uncertainty (e.g. micrometer).

11 Independency principle, envelope requirement and two-point size Examples of drawing notations

12 12 Independency principle, envelope requirement and two-point size 3. Examples of drawing notations Indication above the drawing title block 3.1 No indication Without special agreement, the ISO GPS system standard ISO 8015 is deemed to be agreed, and thus the two-point size method according to ISO as the default for the determination of features of size. Note: As soon as one part of the ISO GPS system (e.g. machining symbols, or shape and location tolerances) has been called up, the whole ISO GPS system is deemed to be agreed (see the 2014 edition of the Standards Compendium). Responsible dept. Technical reference Prepared by: Approved by: Document type Document status Title, additional title Rev. Issue date Lang. Sheet no indication of «ISO 8015» 3.2 Indication ISO 8015 The indications Tolerancing ISO 8015 and Linear sizes ISO have the same consequence as described above. It can however be useful to reference ISO 8015 and ISO , especially to distinguish between old and new drawings. Tolerancing ISO 8015 Linear sizes ISO Responsible dept. Technical reference Prepared by: Approved by: Document type Document status Title, additional title Rev. Issue date Lang. Sheet