Geometrical product specifications(GPS)—Dimensional and geometrical tolerances for moulded parts—Part 3: General dimensional and geometrical tolerances and machining allowances for castings
GB/T 42124.3-2025 Geometrical product specifications (GPS) — Dimensional and geometrical tolerances for moulded parts — Part 3: General dimensional and geometrical tolerances and machining allowances for castings
1 Scope
This document specifies the requirements for taper, draft angle, tolerance grades, surface mismatch, wall thickness tolerance, required machining allowance, indication on drawings and rejection of castings.
This document is applicable to castings produced by various casting processes and using ± tolerances for indicated dimensions.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 131 Geometrical Product Specifications (GPS) - Indication of surface texture in technical product documentation (GB/T 131-2006, ISO 1302:2002, IDT)
GB/T 1182 Geometrical product specifications (GPS) - Geometrical tolerancing - Tolerances of form, orientation, location and run-out (GB/T 1182-2018, ISO 1101:2017, IDT)
GB/T 4458.4 Mechanical drawings - Dimensioning
GB/T 5611 Foundry terminology
GB/T 24744 Geometrical product specifications (GPS) - Drawing indications for moulded parts in technical product documentation (TPD) (GB/T 24744-2009, ISO 10135: 2007, IDT)
GB/T 42124.1 Geometrical product specifications (GPS) - Dimensional and geometrical tolerances for moulded parts - Part 1: Vocabulary (GB/T 42124.1-2022, ISO 8062-1:2007, MOD)
ISO 21920-1 Geometrical product specifications (GPS) - Surface texture: Profile - Part 1: Indication of surface texture[ ISO 1302 has been cancelled and replaced by ISO 21920-1, and there is no technical difference between the referenced contents.]
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 5611 and GB/T 42124.1 and the following apply.
3.1
draft angle
taper
value of inclination (angle) that is added to a geometrical feature of a pattern or mould to ensure the removal of the pattern or moulded part from the mould
3.2
external draft angle
draft angle on a surface that has no opposite surface in the direction outward of the part
3.3
internal draft angle
draft angle on a surface that has an opposite surface in the direction outward of the part
Note: Figure 1 shows the schematic diagrams of internal and external draft angles.
Key:
L1 — length of the external feature;
L2 — length of the internal feature;
αe — external draft angle;
αi — internal draft angle.
Figure 1 Internal and external draft angles
3.4
nominal dimension of casting
design dimensions of rough casting before machining
Note 1: The schematic diagram for indicate the nominal dimensions of rough casting is shown in Figure 2.
Note 2: The schematic diagram of dimensional tolerance and ultimate dimensions of casting (including required machining allowances) is shown in Figure 3.
Key:
1 — nominal dimensions of rough casting.
Figure 2 Drawing indication
Key:
1 — nominal dimensions of rough casting;
2 — dimensions after machining;
3 — minimum limit of dimension;
4 — maximum limit of dimension.
Figure 3 Dimensional tolerances and limits
3.5
dimensional tolerance of casting
allowable variation of dimension of casting
Note: The dimensional tolerance of casting is equal to the absolute value of the difference between the maximum limit of dimension and the minimum limit of dimension, and it's also equal to the absolute value of the difference between the upper deviation and the lower deviation.
Contents
Foreword II
Introduction V
1 Scope
2 Normative references
3 Terms and definitions
4 Abbreviated terms
5 Taper
6 Draft angles
7 Tolerance grades
8 Surface mismatch (SMI)
9 Wall thickness tolerance
10 Required machining allowances (RMA)
11 Indication on drawings
12 Rejection
Annex A (Informative) Comparison of clause/subclause numbers between this document and ISO 8062-3:2023
Annex B (Informative) Technical differences between this document and ISO 8062-3:2023 and their justifications
Annex C (Informative) Dimensional and geometrical tolerances for castings
Annex D (Informative) Application of general geometrical tolerances for castings
Annex E (Informative) Datums for general geometrical tolerances
Annex F (Informative) Selection of required machining allowance grades (RMAG)
Annex G (Informative) Relation to the GPS matrix model
Bibliography
