casting ISO8062

ISO/TC 213 N 160Date: 1997-09-19

ISO/CD 8062-2

ISO/TC 213/WG 9Secretariat: SIS/SMS

Geometrical product specifications (GPS) - Dimensional and geometricaltolerances for moulded parts — — Part 2: Dimensional and geometricaltolerances and machining allowances for castings

WARNING

This document is not an ISO standard. It is distributed for review and comment.It is subject to change withour notice and may not be referred to as an International Standard.

© ISO 1997 - All rights reserved

—

Document type: International StandardDocument subtype: Not applicableDocument stage: (30) CommitteeDocument language: E

F:\USER\AKJ\WP51DOK\GPS\TC213WG9\8062-2.DOC ISOSTD ISO Template Version 3.0 1997-02-07

ISO/CD 8062-2 © ISO

ii

Contents

1 Scope................................................................................................................................................................. 12 Normative reference(s) ..................................................................................................................................... 13 Definitions......................................................................................................................................................... 14 Tolerance grades .............................................................................................................................................. 14.1 Dimensional tolerance grades ...................................................................................................................... 14.2 Geometrical tolerance grades ....................................................................................................................... 24.3 Non-ridgid parts............................................................................................................................................. 55 Mismatch........................................................................................................................................................... 56 Wall thickness................................................................................................................................................... 57 Tapered features............................................................................................................................................... 58 Position of tolerance zone ............................................................................................................................... 59 Required machining allowances, RMA............................................................................................................ 59.1 General ........................................................................................................................................................... 59.2 Grades of required machining allowance .................................................................................................... 89.3 Surfaces pre-machined by the foundry ........................................................................................................ 810 Indication on drawings................................................................................................................................... 810.1 Indication of dimensional casting tolerances ............................................................................................ 810.2 Indication of machining allowances........................................................................................................... 910.3 Indication of geometrical casting tolerances........................................................................................... 1011 Machined surfaces........................................................................................................................................ 10Annex A (informative) Casting dimensional and geometrical tolerances....................................................... 12Annex B (informative) Casting general dimensional and geometrical tolerances ......................................... 15Annex C (informative) Required machining allowance grades (RMA)............................................................ 15Annex D (informative) Symmetry (see clause 4.2) - Examples ........................................................................ 17Annex E (informative) Concepts for general tolerancing of characteristics .................................................. 18Annex F (informative) Former praxis (Tapered features)................................................................................. 19Annex G (informative) Relation to the GPS matrix model ............................................................................... 20Annex H (informative) Bibliography.................................................................................................................. 21

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© ISO ISO/CD 8062-2

iii

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies(ISO member bodies). The work of preparing International Standards is normally carried out through ISO technicalcommittees. Each member body interested in a subject for which a technical committee has been established hasthe right to be represented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.ISO 8062, Part 2, was prepared by Technical Committee ISO/TC 213, Dimensional and geometrical productspecifications and verification.This International Standard cancels and replaces ISO 8062:1994 of which it constitutes a technical revision.Annexes A, B, C, D, E, F, G and H are for information only.


iv

Introduction

This International Standard is a geometrical product specification (GPS) standard and is to be regarded as ageneral GPS standard (see ISO/TR 14683). It influences link 2 of the chain of standards on dimensional andgeometrical tolerances for moulded parts.For more detailed information of the relation of this standard to other standards and the GPS matrix model seeannex A.This International Standard relates to a system of tolerance grades and machining allowance grades for castsmetals and their alloys.The tolerance specified for a casting may determine the casting method. It is therefore recommended, before thedesign or the order is finalized, that the customer liaise with the foundry to discussa) the proposed casting design and accuracy required;b) machining requirements;c) method of casting;d) the number of castings to be manufactured;e) the casting equipment involved;f) datum target system according to ISO 5459;g) casting alloy;h) any special requirements, for instance, individual dimensional and geometrical tolerances, fillet radii

tolerances and individual machining allowances;Because the dimensional and geometrical accuracy of a casting is related to production factors, tolerance gradeswhich can be achieved for various methods and metals are described in Annex A fori) dimensional tolerances long series and mass production, where development, adjustment and maintenance

of casting equipment make it possible to achieve close tolerances;j) dimensional tolerances short series and single production;k) geometrical tolerances.Information on typical required machining allowance grades is given in Annex C.

COMMITTEE DRAFT © ISO ISO/CD 8062-2

1

Geometrical product specifications (GPS) - Dimensional andgeometrical tolerances for moulded parts — — Part 2:Dimensional and geometrical tolerances and machiningallowances for castings

1 Scope

This part of ISO 8062 specifies a system of dimensional and geometrical tolerances as well as required machiningallowance grades for castings as delivered to the purchaser. It is applicable to the dimensional and geometricalaccuracy of castings in all cast metals and their alloys produced by various casting manufacturing processes [seeclause 4 and Introduction h)].This part of ISO 8062 shall apply to both general dimensional and geometrical tolerances referred to in the field ofthe drawing and to individual dimensional and geometrical tolerances directly specified on the drawing (see clause10).Individual geometrical tolerances shall be indicated as specified in ISO 1101.General geometrical tolerance grades in accordance with this part of ISO 8062 should be specified when thefundamental tolerancing principle in accordance with ISO 8015 is used and indicated on the drawing (see AnnexB).

2 Normative reference(s)

The following standards contain provisions which, through reference is this text, constitute provisions of thisinternational standard. At the time of publication, the editions indicated were valid. All standards are subject torevision, and parties to agreements based on this international standard are encouraged to investigate thepossibility of applying the most recent editions of the standards indicated below. Members of IEC and ISOmaintain registers of currently valid international standards.ISO 1101, Technical drawings - Geometrical tolerancing - Tolerancing of form, orientation, location and run-out - Generalities, definitions, symbols, indications on drawingsISO 1302, Technical drawings - Method of indicating surface textureISO 5459, Technical drawings - Geometrical tolerancing - Datums and datum systems for geometricaltolerancesISO 8015, Technical drawings - Fundamental tolerancing principle

ISO 8062-11, General terms for moulded parts

ISO 129-X1, Technical drawings - Indication of linear and angular dimensionsISO 10579, Technical drawings - Dimensioning - Non-rigid parts

3 Definitions

For the purpose of this International Standard, the definitions in ISO 8062-1 apply, as well as the definitions givenin ISO 1101 and ISO 5459.

4 Tolerance grades

4.1 Dimensional tolerance grades

There are 16 casting dimensional tolerance grades, designated CT1 to CT16 (see table 1).

1 Under preparation.


2

Dimensions for which general tolerances are not suitable shall be allocated individual tolerances. See ISO 129-X(ISO 406)2) .

Table 1 — Casting dimensional tolerances

Raw castingbasicdimensionsmm

Total casting tolerance 1)

mm

over up toandinclu-ding

Casting tolerance grade CT 2) 3)

1 2 3 4 5 6 7 8 9 10 11 12 13 4) 14 4) 15 4) 16 4) 5)

-1016

101625

0,090,10,11

0,130,140,15

0,180,20,22

0,260,280,3

0,360,380,42

0,520,540,58

0,740,780,82

11,11,2

1,51,61,7

22,22,4

2,833,2

4,24,44,6

--6

--8

--10

--12

254063

4063100

0,120,130,14

0,170,180,2

0,240,260,28

0,320,360,4

0,460,50,56

0,640,70,78

0,911,1

1,31,41,6

1,822,2

2,62,83,2

3,644,4

55,66

789

91011

111214

141618

100160250

160250400

0,15--

0,220,24-

0,30,340,4

0,440,50,56

0,620,70,78

0,8811,1

1,21,41,6

1,822,2

2,52,83,2

3,644,4

55,66,2

789

101112

121416

161820

202225

4006301000

63010001600

---

---

---

0,64--

0,91-

1,21,41,6

1,822,2

2,62,83,2

3,644,6

567

789

101113

141618

182023

222529

283237

1600250040006300

25004000630010000

----

----

----

----

----

----

2,6---

3,84,4--

5,46,27-

891011

10121416

15172023

21242832

26303540

33384450

42495664

1) See clause 8.2) For wall thicknesses in grade CT1 to CT15, one grade coarser applies (see clause 6).3) See clause 4.4) For sizes up to 16 mm, general tolerances from CT13 to CT16 are not available. For these sizes individual tolerances shall be indicated.5) Grade 16 exists only for wall thicknesses of castings generally specified to CT15.

4.2 Geometrical tolerance grades

There are 7 casting geometrical tolerance grades (CTG) designated CTG 2 to 8 (see tables 2 to 5).NOTE 1 Values are not given for grade CTG 1. This grade is reserved for finer values which may be required in the future.The nominal length to be used in tables 2 to 5 shall be the largest dimension of the considered feature.The datums to be used in tables 4 and 5 shall be the longer of the two features. If the features are of equalnominal length, either may be taken as the datum (examples, see Annex D).When geometrical casting tolerances indicated by a general geometrical tolerance grade are not suitable,individual geometrical casting tolerances shall be allocated.NOTE 2 The application of general tolerances according to this standard, see clause 10, implies the concept given in AnnexE.

Table 2 — Tolerances on straightness

Raw casting nominallength of the feature1)

mm

Total geometrical tolerancemm

Over Up to andincluding

Casting geometrical tolerance grade (CTG)

2 3 4 5 6 7 8

10

30

10

30

100

0,08

0,12

0,18

0,12

0,18

0,27

0,18

0,27

0,4

0,27

0,4

0,6

0,4

0,6

0,9

0,6

0,9

1,4

0,9

1,4

2,0

2) Under preparation, will replace ISO 406:1987.


3

100

300

1000

3000

300

1000

3000

10000

0,27

0,4

-

-

0,4

0,6

-

-

0,6

0,9

-

-

0,9

1,4

2,0

3,0

1,4

2,0

3,0

4,6

2,0

3,0

4,6

6,8

3,0

4,6

6,8

101) When a value is outside the table, individual tolerances shall be indicated.


4

Table 3 — Tolerances on flatness


mm




2 3 4 5 6 7 8

10

30

100

300

1000

3000

10

30

100

300

1000

3000

10000

0,12

0,18

0,27

0,4

0,6

-

-

0,18

0,27

0,4

0,6

0,9

-

-

0,27

0,4

0,6

0,9

1,4

-

-

0,4

0,6

0,9

1,4

2,0

3,0

4,6

0,6

0,9

1,4

2,0

3,0

4,6

6,8

0,9

1,4

2,0

3,0

4,6

6,8

10

1,4

2,0

3,0

4,6

6,8

10


Table 4 — Tolerances on circularity, parallelism, perpendicularity and symmetry


mm




2 3 4 5 6 7 8

10

30

100

300

1000

3000

10

30

100

300

1000

3000

10000

0,18

0,27

0,4

0,6

0,9

-

-

0,27

0,4

0,6

0,9

1,4

-

-

0,4

0,6

0,9

1,4

2,0

-

-

0,6

0,9

1,4

2,0

3,0

4,6

6,8

0,9

1,4

2,0

3,0

4,6

6,8

10

1,4

2,0

3,0

4,6

6,8

10

15

2,0

3,0

4,6

6,8

10

15



5

Table 5 —Tolerances on coaxiality


mm




2 3 4 5 6 7 8

10

30

100

300

1000

3000

10

30

100

300

1000

3000

10000

0,27

0,4

0,6

0,9

1,4

-

-

0,4

0,6

0,9

1,4

2,0

-

-

0,6

0,9

1,4

2,0

3,0

-

-

0,9

1,4

2,0

3,0

4,6

6,8

10

1,4

2,0

3,0

4,6

6,8

10

15

2,0

3,0

4,6

6,8

10

15

23

3,0

4,6

6,8

10

15

23


4.3 Non-ridgid parts

For drawings where the tolerances according to this standard apply in a specified restrained condition it is to bereferred to ISO 10579 onthe drawing.

5 Mismatch

Unless otherwise specified, mismatch shall lie within the tolerance shown in table 1. When it is important to restrictfurther value of mismatch, the maximum value shall be stated on the drawing (see 10.1).

6 Wall thickness

Unless otherwise specified, the tolerance for wall thickness in grades CT1 to CT15 shall be one grade coarser thanthe general tolerance for other dimensions; for example, if there is a general tolerance on a drawing of CT10, thetolerance on wall thicknesses shall be CT11.

7 Tapered features

See ISO 8062-1 and Annex F, Former praxis.

8 Position of tolerance zone

The tolerance zone, unless otherwise stated, shall be symmetrically disposed with respect to a basic dimension,i.e. with one half on the positive side and one half on the negative side (see figure 1).When agreed between manufacturer and purchaser for specific reasons, the tolerance zone may be asymmetric.In such a case the tolerance shall be stated individually, following the basic dimensions.

9 Required machining allowances, RMA

9.1 General

Unless otherwise specified, the required machining allowance is valid for the entire raw casting, i.e. only one valueis specified for all surfaces to be machined, and this shall be selected from the appropriate dimension rangeaccording to the largest overall dimension of the finished casting after final machining (see figure 9).


6

The required machining allowance and the casting tolerance shall be arranged as shown in figures 1 to 4. Whenapplicable, the taper also shall be considered.

PLACE FIGURE HERE

R = Raw casting basic dimensionF = Dimension after final machiningRMA = Required machining allowanceCT = Casting tolerance

Figure 1 — External machining of boss

PLACE FIGURE HERE

Figure 2 — Internal machining

PLACE FIGURE HERE

Figure 3 — Machining of step dimension


7

PLACE FIGURE HERE

Figure 4 — Machining on one side of feature

PLACE FIGURE HERE

Figure 5 — Largest overall dimension of the casting after final machining


8

9.2 Grades of required machining allowance

There are 10 grades of required machining allowance, designated A to K (see table 6).NOTE Grades recommended for particular alloys and manufacturing methods are shown in table C.1 for information only.

Table 6 — Required machining allowances (RMA)

Largestdimension 1)

mm

Required machining allowancemm

Over Up toandincluding

Required machining allowance grade

A 2) B 2) C D E F G H J K-406310016025040063010001600250040006300

40631001602504006301000160025004000630010000

0,10,10,20,30,30,40,50,60,70,80,911,1

0,10,20,30,40,50,70,80,911,11,31,41,5

0,20,30,40,50,70,91,11,21,41,61,822,2

0,30,30,50,811,31,51,822,22,52,83

0,40,40,71,11,41,82,22,52,83,23,544,5

0,50,511,522,533,544,555,56

0,50,71,42,22,83,5455,56789

0,7123456789101112

11,42,845,579101113141617

1,424681012141618202224

1) Largest overall dimension of the casting, after final machining.2) Grades A and B shall only be applied in special cases, for example with series production in which the

pattern equipment, the casting procedure and the machining procedure with regard to clamping surfacesand datum surfaces or targets have been agreed between the customer and the foundry.

3) Sand casting and metallic permanent mould for steel, gray iron, S.G. iron and malleable iron of dimensionof less than equal 100 mm may apply 2 - 3 larger grade of required machining allowance, when requiredmachining allowance of this table is smaller.

9.3 Surfaces pre-machined by the foundry

Any surfaces to be pre-machined by the foundry and the necessary machining allowances for the final machiningshall be stipulated on the drawing by the customer in accordance with ISO 1302.The required machining allowances necessary for the achievement of the pre-machined condition shall be theresponsibility of the foundry, independent of the values given in table 6.

10 Indication on drawings

10.1 Indication of dimensional casting tolerances

Casting tolerances according to this International Standard shall be tested on the drawing in one of the followingways:


9

a) with general information relating to tolerances;EXAMPLE

”General tolerances ISO 8062 - CT12”b) if further restriction of the mismatch is required (see clause 4);

EXAMPLE”General tolerances ISO 8062 - CT12 - maximum mismatch 1,5”

c) if individual tolerances are required following the basic dimension.EXAMPLE

”95 ± 3 ” or "200 "−+

35

10.2 Indication of machining allowances

The surfaces to be machined, the required machining allowance value and, in brackets, the required machiningallowance grade shall be stated on the drawing. These shall be taken into account when the pattern or dieequipment is being produced.Required machining allowances shall be stated on the drawing as follows:a) with general information relating to tolerances and required machining allowances;

EXAMPLEFor a required machining allowance of 6 mm in grade H for a casting in the largest dimension range over 400mm and up to 630 mm (with general tolerance for the casting ISO 8062 - CT12):

”ISO 8062 - CT12 - RMA 6 (H)”and/or

b) on a particular surface on the drawing, if an individual required machining allowance is necessary (see 10.3).EXAMPLESee figure 6.

Figure 6 — Indication of required machining allowance on individual surfaces


10

10.3 Indication of geometrical casting tolerances

Geometrical casting tolerances according to this standard shall be stated on the drawing in one of the followingways:a) When general tolerances in accordance with this part of ISO 8062 apply in conjunction with the general

casting tolerances in accordance with table 1, the following information shall be indicated in or near the titleblock:- ”ISO 8062”- the tolerance grade (CT) in accordance with table 1 and the required machining allowance (RMA) in

accordance with table 6,- the tolerance grade (CTG) in accordance with table 2 to 5.EXAMPLE”ISO 8062 - CT12 - RMA 6 (H) - CTG 7”

NOTE 1 - For the concept of general tolerancing, see clause 1, Scope and Annex E, clause E.4.b) For general geometrical casting tolerances according to table 2:

EXAMPLE”ISO 8062 - CTG 7”

NOTE 2 - For the concept of general tolerancing, see clause 1, Scope and Annex E, clause E.4.c) When individual geometrical tolerances are required, these may be finer or coarser than the general

geometrical tolerances which would normally be applied to the nominal length of the feature, but theparticular tolerance values should be chosen from table 2 to table 5:EXAMPLE

For an individual geometrical casting flatness tolerance of 3 mm, e.g. with a rawcasting nominal length of the feature of 500 mm and the value taken from CTG 6 intable 3.

Figure 7

11 Machined surfaces

For surfaces to be machined the dimensional and geometrical deviations must allow that the finished dimensionsand form can be achieved.NOTE This can lead to a reduction of the size tolerance on the least material limit by the extracted geometrical deviation.

See figure 8.

General tolerancesISO 8062 - CT 11 - RMA 5 (G) - CTG 5


11

Figure 8


12

Annex A(informative)

Casting dimensional and geometrical tolerances

A.1 Tables A.1 and A.2 show dimensional and table A show geometrical tolerance grades which can normally beexpected in casting processes. As indicated in the Introduction to this International Standard, the accuracy of acasting process is dependent upon many factors, including:a) complexity of the design;b) type of pattern equipment or die equipment;c) the metal or alloy concerned;d) the condition of patterns or dies;e) the foundry working methods.A.2 For long series of repetitive work, it may be possible to make adjustments and to control core positionscarefully to achieve dimensional tolerance grades finer than those indicated in table A.1.A.3 In sand casting for short production series and for single castings, it is generally impractical anduneconomical to use metal patterns and to develop equipment and casting procedures resulting in narrowtolerances. The wider tolerances for this class of manufacture are shown in table A.2.A.4 Dimensional tolerances in table 1 are based on foundry data from a number of countries. These data wereused to construct a series of smooth curves using increments of

√ 2 for grades CT1 to CT13, and3 √ 2 for grades CT13 to CT16.

Many dimensions of a casting are affected by the presence of a mould joint or a core, requiring increseddimensional tolerance. Since the designer will not necessarily be aware of the mould and core layour to be used,increases have already been included in table 1.A.5 Geometrical tolerances in table 2 and 5 are based on foundry data from a number of countries.


13

Table A.1 — Casting dimensional tolerance grades for long-series production raw castings

Method Tolerance grade CTCasting material

Steel Greyiron

S.G.iron

Malleable iron

Copperalloys

Zincalloys

Lightmetalalloys

Nickel-basedalloys

Cobolt-basedalloys

Sand cast,hand moulding

11 to 14 11 to 14 11 to 14 11 to 14 10 to 13 10 to 13 9 to 12 11 to 14 11 to 14

Sand cast,machinemoulding andshell moulding


Metalllic perma-nent mould 3)

(except pressuredie casting)

7 to 9 7 to 9 7 to 9 7 to 9 7 to 9 6 to 8

Pressure diecasting 3)

6 to 8 4 to 8 5 to 7

Investmentcasting 4)

4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6

NOTES

1) The tolerance grades indicated are those which can normally be held for castings produced in long seriesand when production factors influencing the dimensional accuracy of the casting have been fully developed.

2) This International Standard can also be applied to processes and materials not cited in this table by

agreement between the producer and the user of the castings.

3) During the life cycle of a die or metallic permanent mould the tolerance grade may be increased with 1tolerance grade.

4) For investment castings applies:over 100 mm grade 4 to 8over 400 mm grade 4 to 9


14

Table A.2 — Casting dimensional tolerance grades for short-series or single-production raw castings

Method Mouldingmaterial

Tolerance grade CT

Casting materialSteel Grey iron S.G. iron Malleabl

e ironCopperalloys

Lightmetalalloys

Nickel-basedalloys

Cobolt-basedalloys

Sandcast,hand-moulded

Clay-bonded

13 to 15 13 to 15 13 to 15 13 to 15 13 to 15 11 to 13 13 to 15 13 to 15

Chemicallybonded

12 to 14 11 to 14 11 to 14 11 to 14 10 to 13 10 to 13 12 to 14 12 to 14

NOTES

1) The tolerance grades indicated are those which can normally be held for castings produced in short seriesor as single castings.

2) The values in this table apply generally to basic dimensions greater than 25 mm. For smaller dimensions,finer tolerances can normally be economically and practically held as follows:

a) basic dimension up to 10 mm: three grades finer;b) basic dimensions 10 mm to 16 mm: two grades finer;c) basic dimensions 16 mm to 25 mm: one grade finer.

3) This International Standard can also be applied to processes and materials not cited in this table byagreement between the producer and the user of the castings.

Table A.3 — Casting geometrical tolerances grades

Method Steel Greyiron

S.G.iron

Malleable iron

Cualloys

Zualloys

Lightmetalalloys

Nibasedalloys

Cobasedalloys





Metalllic perma-nent mould 1)

(except pressuredie casting)

3 to 5 3 to 5

Pressure diecasting 1)

2 to 4 2 to 4 2 to 4

Investmentcasting


1) During the life cycle of a die or metallic permanent mould the tolerance grade may be increased with 1tolerance grade.

2) For investment castings applies:over 100 mm grade 4 to 8over 400 mm grade 4 to 9


15

Annex B(informative)

Casting general dimensional and geometrical tolerances

According to the principle of independency (see ISO 8015), casting general dimensional and geometricaltolerances apply independently of the extracted local size of the casting features. Accordingly, the generalgeometrical tolerances may be used even if the features are everywhere at their maximum material size(see figure B.1).

General tolerancesISO 8062-2 CT10-CTG 6

Figure B.1 — Principle of independency; maximum permissible deviations on the same feature

NOTE The dimensional tolerance is taken from CT 10 and the geometrical tolerances are taken from CTG 6.When the envelope requirement E according to ISO 8015 is individually indicated adjacent to the size dimensionthe envelope requirement shall also be complied with.

Annex C(informative)

Required machining allowance grades (RMA)

RMA grades recommended for particular metals and alloys and manufacturing methods are presented in tableC.1.

Table C.1 — Typical required machining allowance grades for raw castings

Method Required machining allowance gradeCasting materialSteel Grey

ironS.G.iron

Malleable iron

Copperalloys

Zincalloys

Lightmetalalloys

Nickel-basedalloys

Cobolt-basedalloys


G to K F to H F to H F to H F to H F to H F to H G to K G to K


F to H E to G E to G E to G E to G E to G E to G F to H F to H


16

Metallicpermanent mould(except pressuredie casting)

- D to F D to F D to F D to F D to F D to F - -

Pressure diecasting

- - - - B to D B to D B to D - -

Investmentcasting

E E E - E - E E E

NOTES

1) This International Standard can also be applied to processes and materials not cited in this table byagreement between the producer and the user of the castings.


17

Annex D(informative)

Symmetry (see clause 4.2) - Examples

a) Datum: longer feature (l2)

b) Datum: longer feature (l1)

c) Datum: longer feature (l2)

d) Datum: longer feature (l1)

Figure D.1 — Examples of general tolerances on symmetry (datum specified in accordance with clause4.2)


18

Annex E(informative)

Concepts for general tolerancing of characteristics

E.1 General tolerances should be indicated on the drawing by reference to this part of ISO 8062 in accordancewith clause 10.The values of general tolerances correspond to grades of customary foundry accuracy, the appropriate tolerancegrade being selected and indicated on the drawing.E.2 For certain tolerance values, which corresponds to the customary foundry accuracy, there is usually no gainin manufacturing economy by enlarging the tolerance. In any event, foundry machinery and the usual foundry skillnormally do not manufacture features with greater deviations. For example, a feature of 150 mm ± 1,8 mmdiameter by 350 mm long manufactured in a foundry with a customary accuracy equal to or finer than CTG 7contains the geometrical deviations well within 4,6 mm for circularity, 3 mm for straightness of surface elements(the values given have been taken from Tables 3 and 4). Specifying larger tolerances would be of no benefit inthis particular foundry.However, if, for functional reasons, a feature requires a smaller tolerance value than the ”general tolerances”, thenthe feature should have the smaller tolerance indicated individually adjacent to the particular feature. This type oftolerance falls outside the scope of general tolerances.In cases where the function of a feature allows a casting tolerance equal to or larger than the general tolerancevalues, this should not be individually indicated, but should be stated on the drawing as described in clause 10.This type of tolerance allows full use of the concept of general tolerancing.There will be ”exceptions to the rule” where the function allows a larger tolerance than the general tolerances, andthe larger tolerance will provide a gain in manufacturing economy. In these special cases, the larger castingtolerance should be indicated individually adjacent to the particular feature, e.g. the circularity tolerance of a largeand thin ring.E.3 Using general tolerances leads to the following advantages:

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 detailed tolerance calculations as it is sufficient only toknow that the function allows a tolerance greater than or equal to the general tolerance;c) the drawing readily indicates which features can be produced by normal process capability, which alsoassists quality engineering by reducing inspection levels;d) those features remaining, which have individually indicated casting tolerances, will, for the most part, bethose controlling features for which the function requires relatively small tolerances and which therefore maycause special effort in the production - this will be helpful for production planning and will assist quality controlservices in their analysis of inspection requirements;e) purchasers can negotiate orders more readily since the ”customary foundry accuracy” is known before thecontract is placed; this also avoids arguments on delivery between the buyer and the supplier, since in thisrespect the drawing is complete.

These advantages are fully obtained only when there is sufficient reliability that the general dimensional as well asgeometrical tolerances and RMA will not be exceeded, i.e. when the customary foundry accuracy of the particularfoundry is equal to or finer than the general tolerances indicated in the drawing.The foundry should, therefore,

- determine by measurements what its customary foundry accuracy is;- accept only those drawings having general tolerances equal to or greater than its customary foundryaccuracy;- determine by sampling that its customary foundry accuracy does not deteriorate (it is not the intention ofthe concept of general tolerancing to check every feature on every casting).

Relying on undefined ”good foundry” with all its uncertainties and misunderstandings is no longer necessary withthe concept of general tolerances. The general tolerances define the required accuracy of ”good foundry”.E.4 The tolerance the function allows is often greater than the general tolerance. The function of the parts is,therefore, not always impaired when the general tolerance is (occasionally) exceeded at any feature of the casting.Exceeding the general tolerance should lead to a rejection of the casting only if the function is impaired.E.5 It is not the intention of the concept of general tolerances, according to this standard, to inspect each generaltolerance on each casting because it is unlikely that the general tolerance will be exceeded.


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Annex F(informative)

Former praxis (Tapered features)

In ISO 8062:1994 the following clause concerning tapered features was included. It is replaced by thecorresponding clause in ISO 8062-1.Where a design requires a tapered feature (e.g. feature with a draft angle), the tolerance shall be appliedsymmetrically along the surface (see figure 4).

Figure F.1 — Tolerance zone on tapered featuresThe drawing shall specify generally whether the taper shall be added to, subtracted from or averaged to thematerial, e.g.

taper +, figure 4 a)taper -, figure 4 b)taper ±, figure 4 c)

Tapers for particular surfaces arranged differently from the general arrangement of taper of the drawing shall beindicated individually at the surface, e.g.For dimensions to be machined, ”taper +” shall be applied, irrespective of the general drawing specification fortaper, in order that the finished dimensions can be achievable.


20

Annex G(informative)

Relation to the GPS matrix model

For full details about the GPS matrix model see ISO/TR 14638.

G.1 Information about the standard and its useISO 8062-2 is a revision of ISO 8062:1994 and with an addition of values for geometrical tolerances for castings.

G.2 Position in the GPS matrix modelThis International standard is a General GPS standard, which influences the chain link 2 of the chain of standardson datums in the General GPS matrix, as graphically illustrated on figure G.1.

GLOBAL GPS STANDARDS

FUNDA- GENERAL GPS MATRIX

MENTAL Chain link number 1 2 3 4 5 6

Size

Distance

GPS Radius

Angle

STAN- Form of line independent of datum

DARDS Form of line dependent of datum

Form of surface independent of datum

Form of surface dependent of datum

Orientation

Location

Circular run-out

Total run-out

Datums

Roughness profile

Waviness profile

Primary profile

Surface defects

Edges

Figure G.1 G.3 Related standardsThe related standards are those of the chains of standards indicated in figure G.1.


21

Annex H(informative)

Bibliography

[1] ISO/TR 14638:1995, Geometrical Product Specifications (GPS) - Masterplan[2] ISO 2768-2:1989, General tolerances - Part 2: Geometrical tolerances for features without individual

tolerance indications

Documents

casting ISO8062