1 Scope
This standard specifies the tolerance grades and required machining allowance grades for the dimensions of castings.
This standard is applicable to the dimensions of cast metals and their alloys produced by various casting manufacturing processes.
This standard applies both to general tolerances and/or general required machining allowances given on a drawing and to individual tolerances and/or individual required machining allowances which are shown immediately following a specific dimension.
This tolerance system shall be applied when the foundry provides the pattern or die equipment or accepts responsibility for proving it.
2 Normative References
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.
ISO 1302: 1992 "Technical Drawings—Method of Indicating Surface Texture"
3 Definitions
For the purposes of this standard, the following definitions apply.
3.1 Basic dimension
Dimension of a raw casting before machining (see Figure 1), the necessary machining allowance being included (see Figure 2).
3.2 Dimensional tolerance
The allowable variation of dimension. The tolerance is equal to the absolute value of the algebraic difference between the maximum limit of size and the minimum limit of size and it's also equal to the absolute value of the algebraic difference between the upper deviation and the lower deviation.
3.3 Mismatch
Relative displacement of surfaces of a casting owing to inaccuracies in the constituent parts of multipart moulds (see Figure 3)
3.4 Required machining allowance, RMA
On raw castings, a material allowance to permit the removal of the effects of casting on the surface by subsequent machining and to allow the achievement of the desired surface texture and the necessary accuracy of dimension.
With cylindrical features or machining on both sides, the RMA is taken into account twice (see Figure 5 and Figure 6).
3.5 Draft angle (taper)
Additional slope of shaping elements (e.g. on enveloping surfaces) parallel to the pattern drawing direction necessary to facilitate the removal of a casting from a mould or die, or a mold core from a core box
3.6 Wall thickness
The wall thickness refers to the thickness of the casting wall constructed between casting moulds, between casting mould and mold core as well as between the mold cores
Contents
Foreword I
ISO Foreword II
Introduction III
1 Scope
2 Normative References
3 Definitions
4 Dimensioning
5 Tolerance Grades
6 Mismatch
7 Wall Thickness
8 Tapered Features
9 Position of Tolerance Zone
10 Required Machining Allowance, RMA
11 Indication on Drawings
Appendix A (Informative) Casting Tolerances
Appendix B (Informative) Required Machining Allowance (RMA)
Appendix C (Informative) Bibliography
GB/T 6414-1999 引用如下标准：
*ISO 1302: 1992 "Technical Drawings-Method of Indicating Surface Texture"
