GB/T 4249-2018Geometrical product specifications (GPS) -- Fundamentals -- Concepts, principles and rules (English PDF)

4.4 Functional level of workpiece

It is assumed that the workpiece 100% meets the function within the tolerance

limit; does not meet the function outside the tolerance limit.

5.1 Principle for adoption

Once it adopts one part of ISO GPS system in mechanical engineering product

documents, it is equivalent to adopting the entire ISO GPS system, unless

otherwise stated in the document, for example, "refer to other related

documents".

"Unless otherwise stated in the document" means that if the regional, national

or enterprise standards referred are marked in the document, it shall use those

standards. Do not adopt ISO GPS system to interpret the normative elements

specified in the standard.

If it is unnecessary to adopt ISO GPS system, "noting method is according to

GB/T 4249" may selectively mark within the title bar or near the title bar.

NOTE 1: The most common way to adopt ISO GPS system is to use one or more GPS

specifications in drawing.

NOTE 2: ISO GPS system is an International standard issued by ISO/TC 213, see GB/T

20308.

NOTE 3: "Adopting the entire ISO GPS system" means that unless otherwise specified, if

GPS fundamental standard and GPS comprehensive standard are adopted, then the

reference temperature specified in GB/T 19765-2005 and the rules for determination

specified in GB/T 18779.1 shall be adopted. The purpose of "principle for adoption" is to

provide formal traceability for those GPS standards and rules.

5.2 Principle for hierarchy of GPS standard

ISO GPS system is hierarchical. Its standard variety, according to hierarchy,

contains the following types:

- GPS fundamental standard;

- GPS comprehensive standard;

- GPS general standard;

5.4 Key element principle

One workpiece can be considered to be composed by many key elements that

are limited by natural boundaries. Under the situation of default, each GPS

specification of one key element applies to the entire key element. Each GPS

specification that expresses the relationship between many key elements

applies to many key elements. Each GPS specification is only applicable to one

key element or one relationship between key elements.

If it is necessary to change this default specification, it needs to clearly mark on

the drawing.

NOTE 1: The natural boundaries between key elements usually refer to the boundaries

that sudden change happens on the surface normal. But it is not always true. If one

workpiece is composed of two hemispherical elements that have same diameter and

intermediate cylindrical element, in such case, the surface normal of natural boundaries

between key elements does not have sudden change.

NOTE 2: Some marks do not apply to the entire key element, for example, partial area of

key element is marked with a long thick dotted line or is marked with ACS (any cross

section).

NOTE 3: Some marks apply to many key elements, for example, CZ (combined tolerance

zone) is marked.

NOTE 4: Unless otherwise specified, GPS general specification is considered as a series

of GPS specifications. Each GPS specification is only applicable to one characteristic of

key element or relationship between key elements (see 5.12).

5.5 Independence principle

Under the situation of default, GPS specification of each key element or GPS

specification of relationship between key elements is independent from other

specifications. They shall be met respectively, unless other standards or special

marks are specified in the actual product specification (for example, modifier

symbol oM in GB/T 16671, CZ in GB/T 1182 and oE in ISO 14405-1).

5.6 Decimal point principle

The numerical values after the decimal point of nominal size and tolerance

value that are not indicated shall be zero. This principle is applicable to the

drawing and GPS standard.

Example 1: +/-0.2 is equivalent to +/-0.200000...

Example 2: 2:10 is equivalent to 10.000000...

5.7 Default principle

eliminate any ambiguity of the functional description in the specification.

A complete specification operator defines every important detail to be measured

for the specification. Therefore, it eliminates the ambiguity of the specification.

Inspection of operation is an actual application of specification operator. When

the method uncertainty is zero, inspect the sequences of operator and

specification operator which shall be in one-to-one correspondence. When the

method uncertainty is not zero, there are differences in two operators or the

sequence of two specifications.

Although the inspection operator is not marked in the drawing, it shall get close

to the specification operator during the inspection process, so as to ensure the

method uncertainty within the allowable range.

5.10.2 Description of duality principle

The duality principle points out:

a) the GPS specification operator that is specified by GPS specification is

irrelevant to any measuring procedures or measuring instruments;

b) the inspection operator that is to realize GPS specification operator is

irrelevant to the GPS specification itself; but the relationship between it

and GPS specification operator is mirror correspondence.

GPS specification does not specify which kind of inspection operator is

acceptable. Whether the operator is acceptable or not is inspected by

measuring the uncertainty and specification uncertainty.

5.11 Function control principle

The function of each workpiece is described by function operator. It can be

simulated by a series of specification operators. These specification operators

once again define a series of measuring and relevant tolerances.

When all functional requirements of workpiece have been clearly described and

controlled by GPS specification, such specification is complete. In most cases,

since some functions are described / controlled imperfectly, the specification

might be incomplete. Therefore, the correlation between function and a series

of GPS specifications may be superior or inferior.

Any correlation deficiency between any functional requirements and GPS

specification shall cause the uncertainty of function description.

5.12 General specification principle

For each characteristic that has same type and the relationship between each

When the actual specification of any geometric characteristic in the drawing is

ISO basic GPS specification that is marked according to GB/T 1182, GB/T 131-

2006, GB/T 17851, and when in or near title bar, altered default general GPS

specification is not marked, then ISO default specification operator is required

by a current ISO standard that defines corresponding default specification

operator. When establishing drawing, the ISO standard that specifies

corresponding default specification operator shall be the latest version. If other

earlier versions of ISO standard are required to use, it shall be indicated clearly.

NOTE: At present, ISO GPS standard does not give default provisions on all specification

operations in all specification operators, so some ISO default specification operators are

incomplete.

6.3 Altered default GPS specification

One altered default specification operator shall be defined in relevant document.

As a part of a complete specification operator, altered default specification

operator shall be rigorously, clearly and completely defined.

Altered default specification operator shall be marked in or near title bar of

drawing. When non-ISO GPS standard is applied, it shall at least mark the

following information:

- indicate "marking method" or "marking method is according to GB/T 4249";

- symbol ;

- complete identifier of relevant document and other necessary information

(such as date of release).

NOTE: AD represents "altered default".

If altered default specification operator in drawing is more than one, a number

is needed to add after each symbol.

Some ISO standards provide to adopt altered ISO default mode, for example

"Size ISO 14405 ".

symbol only applies to non-ISO GPS standard.

defined in default specification operator.

NOTE 1: The type of the added supplementary information (requirements) shall be defined

by specification modifier (see GB/Z 24637.2).

According to ISO basic specification, in the marked specific specification

operator, the operator that is not specified by the supplementary provisions

shall be still defined by default specification.

NOTE 2: At present, ISO GPS standard does not give default provisions on all specification

operations in all specification operators, so some ISO basic specifications are incomplete.

The contents specified in 7.2 shall be applied to the marks of the following two

specific specification operators:

- testing key elements that are comply with GB/T 1182, GB/T 131-2006, GB/T

7.2 Additional supplementary information (requirements) of ISO basic

specification

When necessary, the additional supplementary information (requirements) of

ISO basic specification can change the default operation of ISO basic

specification, for example:

a) fitting rule;

b) filter type;

c) transmission band;

d) probe tip;

e) extraction condition.

When these default specifications are changed for specific design needs, ISO

basic specification shall use the following modes to modify:

- for GB/T 1182, add information to the second block of the tolerance marking

box;

- for GB/T 131-2006, add information in a~e areas of graphic symbol that the

surface structure is complete;

- for ISO 14405-1, add modifier to tolerance mark.

See corresponding standards for details.

......