is 13099 1991 iso 5458 1987 technical drawings - geometrical tolerancing positional...

Indian Standard

IS 13099 : 1991 IS0 5458 : 1987

TECHNICAL DRAWINGS - GEOMETRICAL TOLERANCING - POSITIONAL

TOLERANCING

UDC 744 : 621.753-l

8 BIS 1991

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

July 1991 Price Qroup 7

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IS 13099: 1991 IS0 5458: 1987

Indian Standard

TECHNICAL DRAWINGS - GEOMETRICAL TOLERANCING - POSITIONAL

TOLERANCING’

NATIONAL FOREWORD

This Indian Standard which is identical with IS0 5458 : 1987 ‘Technical drawings - Geometrical tolerancing - Positional tolerancing’, issued by the International Organrzation for Standardization ( IS0 ), was adopted by the Bureau of Indian Standards on the recommendation of the Drawing Sectional Committee ( LMD 02 ) and approval of the Light Mechanical Engineering Division Council.

In the adopted standard certain terminology and conventions are not identical with those used in Indian Standards; attention is especially drawn to the following:

a) Wherever the words ‘International Standard’ appear referring to this standard, they should be read as ‘Indian Standard’.

b) Comma ( , ) has been used as a decimal marker, while in Indian Standards, the current prac- tice is to use a point ( . ) as the decimal marker.

CROSS REFERENCES

In this adopted standard, reference appears to certain International Standards for which Indian Standards also exist. The corresponding Indian Standards which are to be substituted in their place are listed below along with their degreebf equivalence for the editions indicated:

International Standard Indian Standard Degree of Equivalence

Identical IS0 1101 : 1983

IS0 2692 : 1988

IS0 3098 - 1 : 1974

IS0 5459 : 1981

IS0 8015 : 1985

IS 8000 ( Part 1 ) : 1985 Geometrical tolerancing on technical drawings : Part 1 Tolerancing of form, orientation, location and run-out and appropriate geometrical definitions ( first revision )

IS 8000 ( Part 2 ) : 1991 Geometrical tolerancing on technical drawings : Part 2 Maximum material principle ( first revision )

IS 9609 ( Part 1 ) : 1983 Lettering on technical drawings : Part 1 English characters

IS 10721 : 1983 Datum and datum systems for geometrical tolerancing on technical drawings

IS 12160 : 1987 Technical drawings - Fundamental tolerancing principle

Identical

Identical

Identical

Identical

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As in the Original Standard, this Page is Intentionally Left Blank


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IS 13099 : 1991 IS0 5458 : 1987

0 Introduction

0.1 The concept of positional toleraclcing, described in

IS0 1101, is further elaborated in this Internatjwl Standard.

The figures in this International Standard seree to illustrate the

subjeft matter only and are not necessarily complete.

Other relevant international Standards, such as thope dealing

with the maximum material principle (IS0 26921, datums and datum systems (IS0 54591, should be taken into consideration

wht,ri losing this International Standard.

0.2 For the purposes of this International Standard, all

dimensions and tolerances on the drawings have been sten-

tilled in upright lettering. It should be understood that these in-

dications could just as well be written in free-hand or inclined (italic) lettering without altering the meaning of the indications.

For the presentation of lettering [proportions and dimensions), see IS0 3098-l.

1 Scope and field of application

rhis International Standard describes the principle of positional

,olerancing for the location of features and also provides for-

mulae for the calculation of tolerance values appropriate tn

mating parts. Generally positional tolerancing is applicable to

both regular- and irregular-shaped teatures. However, to make

this lnternetional Standard more comprehensible, only regular- shaped features have been shown.

NOTE - Regular-shaped features are. for example, cvltndrtcal land square) holes, bolts, studs or pins. parallei sided slots and laps, keys and keyways

2 References

IS0 1101, Technical drawings - Geometrical tolerancing -~-

Tolerancing of form, orientation, locahan and run out -.

Generalities, definitions, symbols, indications on drawings

IS0 2692, Technical drawings Geometrical toleranclng

Maximum material principle. 1)

IS0 3098 1, Technical drawmgs -- Letters Parr 1 : Currently

used characters.

IS0 5459, technical drawings ~ Geometncaf tolerancurg -

Dalums and datum-systems for geometrtc tolerances

IS0 8015, Technical drawings Fundam~n tal tolerancu,g prim

ciple.

J At present at the srage of draft. (Revision of IS0 1101-2 1974.)

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IS 13099: 1991 IS0 5458 : 1987

3 Establishment of positional tolerances

3.1 General

The primary constituents are theoretically exact dimensions, tolerance zones and datums.

3.2 Fundamental principle

In the method of positional tolerancing, theoretically exact dimensions and positional tolerances determine the location of features,

such as points, axes and median planes, relative to each other or in relation to one or more datums. The tolerance zone is sym-

metrically disposed about the theoretically exact location.

NOTE - By virtue of this principle positional tolerances do not accumulate where theoretically exact dimensions are arranged in a chain (see figure 4)

(This contrasts with dimensional tolerances arranged in a chain.) Positional tolerancing allows clear reference to be made to one or more datum5

3.3 Positional tolerances related to a specified datum

If the positional tolerance zone is perpendicularly related to a specified datum, the right angle need not be indicated on the drawing

(see figure 1).

Indication on the drawing Interpretation

a) b) c) d)

NOTE - Interpretations at, b). c) or d) may apply at each individual

hole.

a) Axis of hole coincident with theoretically exact location (zero

deviation).

b) Axis of hole at maximum position deviation with zero perpen

dicularity deviation.

c) Axis of hole at maximum position deviatton with maxImum

perpendicularity deviation.

d) Axis of hole at maximum position deviation; I” this CUSP a con,

bination of geometrical deviations.

Figure 1

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IS 13099: 1991 IS0 5458 : 1987

3.4 Positional tolerances on a complete circle

For positional toleranced features arranged in a complete circle, for example, holes on a pitch circle, it is understood that they are equally spaced, unless otherwise stated, and that their locations are theoretically exact.

If two or more groups of features are shown on the same axis, they shall be considered as a single pattern, unless otherwise stated by an appropriate instruction [see figures 2a) and 2b)l.

4x815

Figure 2al

Angular location

optional

Figure 2b)

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IS 13099 : 1991 IS0 5458 : 1987

3.5 Positional tolerances in one direction only

The tolerance value can be specified in one direction; the width of the tolerance zone is then in the direction of the arrow line Isee

figures 3a) and 3b)l.

Indication on the drawing

u- A

Figure 3el

Interpretation

Each of the lines shall be contained within a tolerance zone

defined by two parallel straight lines 0.1 apart which are sym

metrically disposed about the theoretically exact position of

each scale line.

.

Figure 3b)

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IS 13099 : 1991

IS0 5458 : 1087

3.6 Positional tolerances in two directions

Tht: tolerance value can be specified in two directions perpendicular to each other, reference being made to unequal values [see

figt:r<:s 4a) ar~;i 4b)l or equal values lsee figures 5a) and 5b)l.


Figure 4aI

Interpretation

The axis of each hole shall lie within a rectangular tolerance

zone of section 0,3 x 0,l; the axes of the rectangular tolerance

zones are fixed by theoretically exact dimensions.

Figure 4bl

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IS 13099: 1991 is0 5458 : 1987


Figure !5al

Interpretation

The axis of each hole shall lie within a square tolerance zone of section 0,l x 0,l; the axes of the square tolerance zones are fixed by theoretically exact dimensions.

Figure 5bI


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IS 13099 : 1992 IS0 5458 : 1987

3.7 Positional tolerances in all directions

The tolerance can be specified as a cylindrical zone [see figures 6a) and 6b)l.


Jl, 30 cl cy 30 q _ 30

Figure 6a)

Interpretation

L 30 I I= 30 _I_ 30

The axis of each hole shall lie within a cylindrical tolerance zone of diameter 0,l; the axes of the cylindrical tolerance zones are fixed by theoretically exact dimensions.

Figure 6b)

This tolerancing~ method achieves a larger zone than the coordinate method whichean only generate a square (or rectangular) to!erance zone (see figure 7).

NOTE - For cylindrical features of mating parts, the tolerance zone is usually cylindrical, as the tolerance is multi-directional from the theoretically exact location.

-57 % larger zone

Figure 7

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IS 13099 : 1991 IS0 545% : 1987

4 Tolerance combinations

.

4.1 If a group of features is individually located by positional tolerancing and their pattern location by coordinate tolerances, each requirement shall be met independently [see figure 8a)l.

4.1.1 The distances between the actual axes of each left-hand hole and the left-hand edge shall lie between the two limits of size, 173 and 18.5. (Two-point measurement, see IS0 8015.1

The distances between the actual axis of each lower hole and the bottom edge shall lie between the limits of size, 15,5 and 165 [see figures 8a) and 8b)l.

4.1.2 The actual axis of each hole shall lie within the cylindrical tolerance zone of diameter 0.2; the positional tolerance zones are located in their theoretically exact location to each other [see figure &)I.


4.x 06

Figure 8aI

Interpretation

00,2

.- (pm

z

&I

90” 90”

!!!!I+ 20

Figure 8b) Figure 8~)

NOTE - This method is subject to other possible interpretations. If more specific interpretation is desirable, powtronal toleranong and datum indica

tion may be used (see 4.21.

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IS 13099 : 1991 JSO 5458 : 1987

.

4.2 If a group of features is individually located by positional tolerancing and their pattern location is also located by positional tolerancing, each requirement shall be met independently (see figure 9a)l.

4.2.1 The actual axis of each of the four holes shall lie within the cylindrical tolerance zone of diameter 0.01; the positional tolerance zones are located in their theoretically exact positions to each other and perpendicular to datum A [see figure 9b)I.

4.2.2 The actual axis of each hole shall lie within the cylindrical tolerance zone of diameter 0,2; the positional tolerance zones are located in their exact theoretical positions in relation to the simulated datums Y and Z [see figure 9c)l.


6 o,o,_k--- pt 8’

90” 90” +lYf?ir L-h 35

Figure 9b)

Figure 9aI

Interpretation

i Simulated datum 2

Figure 94


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IS 13099 : 199-l IS0 5458:1987

5 Calculation of positional tolerances

5.1 Formulae for determining the required positional tolerances for internal and external features of mating parts to ensure that the parts will assemble are given in this clause.

It is assumed for the calculations of these formulae that both internal and external features are of perfect form and orientation and at their,maximum material condition. On this basis, the formulae will give a “no interference, no clearance” fit when the mating features are at maximum material condition (MMC) and at their most unfavourable location within their positional tolerance zones.

5.2 For calculating positional tolerances, the tollowing two general cases exist :

a) Floating fastener

Two or more parts to be assembled with fasteners, such as bolts and nuts. where all parts have clearance holes for the bolts (see figure 10).

Figure 10

b) Fixed fastener

One of the parts to be assembled has restrained fasteners, such as studs or bolts screwed into threaded holes lsee figure 1 la)] or a dowel pin with an interference fit at one end lsee figure 1 lb)].

Figure lla) Figure 1lbJ

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IS 13099: 1991

IS0 5458 : 1987

1 5.3 The following symbols are used in the formulae :

1 F = maximum material size of the external feature, e.g. the maximum diameter of the fastener

H = maximum material size of the internal feature, e.g. the minimum diameter of the clearance hole

T = positional tolerance (see figure 12)

F 7 Figure 12

5.4 The value of the positional tolerance is calculated using one of the following formulae :

- For floating fasteners :

T=H-F

- For fixed fasteners :

H-F T=--

2

5.5 The formulae given in 5.4 also apply to keys and their mating slots, either,for floating keys or fixed (interference) keys.

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