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IS 919 ( Part 1 ) : 1993IS0 286-l : 1988 Indian Standard IS0 SYSTEM OF LIMITS AND FITSf’ART BASES OF 10LERANCES. DEVIATIONS AND FITS ( Second Revision) Third Reprint JUNE 1997UDC 621*753-l/-2 @I BIS 1993 BUREAU OF INDIAN STANDARDS MANAK BHAVAN,9 BAHADUR SHAH ZAFAR MARGNEW DELHI 110002 May 1993 Prioe Group 11 ( Reaffirmed 1998 ) Engineering Standards Sectional Committee, LM 01 CONTENTS 0 1 23456789 10 introduction. . .. . .. . .Scope. . . . . .. . .Field of application. . . .. . . References . . .. . .. . . Terms and definitions. . .. . .. . .Symbols, designation and interpretation of tolerances, deviations and fits . . .Graphical representation. . .. . . L I Reference temperature. . . .. . . . . .Standard tolerances for basic sizes up to 3 150 mm . . .. . .Fundamectal dc,viations for basic sizes up to 3 150 mm. . .Bibliography. . .. . .. . .Page1111269IOIOIO16 Annexes A Bases of the IS0 system of limits and fitsB Examples of the use of IS0 2S6-1 . . .C Equivalent terms. . .. . .. . .17. . .. . .23. . . * . 26NATIONAL FOREWORbThis Indian Standard ( Second Revision ) which is identical with IS0 236-I : 1988 ‘IS0system of limits arid fits - Part 1 : Bases of tolerances, deviations and fits’ was adopted by theBureau of Indian Staridards on the recommendations of the Engineering Standards SectionalComm,ittee ( LM 01 ) and approval of the Light Mxhanical Engineering Division Council.The standard was srcinally published in 1959. It was subsequently revised in 1963 takingassistance from ISO/R 286-1962 ‘IS0 system of limits and fits, general tolerances anddeviations’.This revi’sion has been made to harmonize the standard with IS0 286-I : 1988. in the presentrevision following have been incorporated:a’) Two additional grtides, that is, IT 17 and IT 18.b) Method of transmitting the information on equipment with limit character such as telex.c) Certain additional ‘tolerance classes.d) Informatioll for sizes up to 3 150 mm.e) Deviations requirement of most commoil shafts and holes such as cd, CD, ef, EF, fg. FGfor sizes up to IO mm which were earlier being covered in IS 919 ( Part 2 ) : 1979‘Recommendations for ,limits and fits for engineering : Part 2 Fine mechanism andhorology’.IS 2709: 1982 ‘Guide for the selection of fits ( first revision )’ and !S 8841 : 1978‘Recommendations for iimits and fits for sizes above 3 150 mm up to 10 000 mm’ are the relatedpublished Indian Standards to this subject. ( Continued on third cover ) IS 919 (Part 1) : 1993IS0 288 - 1 : 19880 Introduction Indian Standard IS0 SYSTEM OF LIMITS AND FITS PART 1 BASES OF TOLERANCES, DEVIATIONS AND FITS( Second Revision ) The need for limits and fits for machined workpieces wasbrought about mainly by the inherent inaccuracy of manufac-turing methods, coupled with the fact that “exactness” of sizewas found to be unnecessary for most workpieces. In orderthat function could be satisfied, it was found sufficient tomanufacture a given workpiece so that its size lay within twopermissible limits, i.e. a tolerance, this being the variation insize acceptable in manufacture.Similarly, where a specific fit condition is required betweenmating workpieces, it is necessary to ascribe an allowance,either positive or negative, to the basic size to achieve the re-quired clearance or interference, i.e. a “deviation”.With developments in industry and international trade, itbecame necessary to develop formal systems of limits and fits,firstly at the industrial level, then at the national level and laterat the international level.This International Standard therefore gives the internationallyaccepted system of limits and fits.Annexes A and B give the basic formulae and rules necessaryfor establishing the system, and examples in the use of thestandard are to be regarded as an integral part of the standard.Annex C gives a list of equivalent terms used in IS0 286 andother International Standards on tolerances. 1 Scope This part of IS0 286 gives the bases of the IS0 system of limitsand fits together with the calculated vaiues of the standardtolerances and fundamental deviations. These values shall betaken as authoritative for the application of the system (see alsoclause A. 1).This part of IS0 286 also gives terms and definitions togetherwith associated symbols. 2 Field of application The IS0 system of limits and fits provides a system oftolerances and deviations suitable for plain workpieces.For simplicity and also because of the importance of cylindricalworkpieces of circular section, only these are referred to ex-plicitly. It should be clearly understood, however, that thetolerances and deviations given in this international Standardequally apply to workpieces of other than circular section.In particular, the general term “hole” or “shaft” can be takenas referring to the space contained by (or containing) the twoparallel faces (or tangent planes) of any,&orkpiece, such as thewidth of a slot or the thickness of a key.The system also provides for fits between mating cylindricalfeatures or fits between workpieces having features withparallel faces, such as the fit between a key and keyway, etc.NOTE - It should be noted that the system is not intended to providefits for workpieces with features having other than simple geometricforms.For the purposes of this part of IS0 286, a simple geometric formconsists of a cylindrical surface area or two parallel olanes. 3 References NOTE - See also clause 10.IS0 1, Standard reference temperature for industrial lengthmeasurements. IS0 286-2, IS0 system of limits and fits - Part 2: Tables ofstandard tolerance grades and limit deviations for holes andshafts. ISOIR 1938, !SO system of limits and fits - Inspection of plainworkpieces. l) IS0 8015, Technical drawings - Fundamental tolerancingprinciple. 1) At present under revision. IS 919 (Part 1) : 1993 IS0 288 - 1: 1988 4 Terms and definitions For the purposes of this International Standard, the followingterms and definitions apply. It should be noted, however, thatsome of the terms are defined in a more restricted sense than incommon usage.4.1 shaft: A term used, according to convention, todescribe an external feature of a workpiece, including featureswhich are not cvlindrical (see also clause 2).4.1.: basic shaft: Shaft chosen as a basis for a shaft-basissystem of fits (see also 4.11.1).For the purposes of the IS0 system of limits and fits, a shaft theupper deviation of which is zero. 4.2 hole : A term used, according to convention, to describean internal feature of a workpiece, including features which arenot cylindrical (see also ciause 2).4.2.1 basic hole: Hole chosen as a basis for a hole-basissystem of fits (see also 4.11.2).For the purposes of the IS0 system of limits and fits, a hole thelower deviation of which is zero.4.38 size: A number expressing, in a particular unit, thenumerical value of a linear dimension.4.3.1 basic size; nominal size: The size from which thelimits of size are derived by the application of the upper andlower deviations (see figure 1). NOTE - The basic size can be a whole number or a decimal number,e.g. 32; 15; 8.75; 0.5; etc. 4.3.2 actual size: The size of a feature, obtained bymeasurement.4.3.2.1 actual local size: Any individual distance at anycross-section of a feature, i.e. any size measured between anytwo opposite points.4.3.3 limits of size: The two extreme permissible sizes of afeature, between which the actual size should lie, the limits ofsize being inctuded.4.3.3.1 maximum limit of size: The greatest permissiblesize of a feature (see figure 1).4.3.3.2 minimum limit of size: The smallest permissible sizeof a feature (see figure 1).4.4 limit system : A system of standardized tolerances anddeviations. 4.5 zero line : In a graphical representation of limits and fits,the straight line, representing the basic size, to which the devi-ations and tolerances are referred (see figure 1).According to convention, the zero line is drawn horizontally,with positive deviations shown above and negative deviationsbelow (see figure 2). Zero line (4.5) Figure 1 - Basic size, and maximum and minimumlimits of size4.6 deviation: The algebraic difference between a size(actual size, limit of size, etc.) and the corresponding basic size. NOTE - Symbols for shaft deviations are lower case letters (u, ei) ndsymbols for hole deviations are upper case letters (ES, El) (seefigure 2). 4.6.1 limit deviations : Upper deviation and lower deviation.4.6.1.1 upper deviation (ES, es): The algebraic differencebetween the maximum limit of size and the corresponding basicsize (see figure 2).4.6.1.2 lower deviation (EI, 4: The algebraic differencebetween the minimum limit of size and the corresponding basicsize (see figure 2).4.6.2 fundamental deviation : For the purposes of the IS0system of limits and fits, that deviation which defines theposition of the tolerance zone in relation to the zero line (seefigure 2).NOTE - This may be either the upper or lower deviation, but, accord- ing to convention, the fundamental deviation is the one nearest thezero line. 4.7 size tolerance: The difference between the maximumlimit of size and the minimum limit of size, i.e. the differencebetween the upper deviation and the lower deviation.NOTE - The tolerance is an absolute value without sign. 2
