ISO 8062-3:2023

Overview

ISO 8062-3:2023 is an ISO Geometrical Product Specifications (GPS) standard that defines general dimensional and geometrical tolerances and machining allowance grades for castings specified with ± tolerances for indicated dimensions. It applies to cast metals and alloys produced by all casting processes and is intended for use when tolerances are referenced in or near the drawing title block (general tolerancing). The standard does not apply to 3D CAD models without indicated dimensions and excludes angular tolerances, cylindricity and other position tolerances not listed.

Key topics and technical requirements

• Scope of tolerances: Linear dimensional tolerances and a focused set of geometrical tolerances - straightness, flatness, roundness, parallelism, perpendicularity, symmetry and coaxiality.
• Tolerance grades and selection: System of dimensional casting tolerance grades (DCT/DCTG) and geometrical casting tolerance grades (GCT/GCTG) to select appropriate tolerance values for cast parts.
• Machining allowances: Required machining allowance (RMA) grades and guidance (RMAG) for finishing castings as delivered to the purchaser.
• Draft angles (taper): Definitions and tables for draft angles (external and internal), plus rules for indicating taper on drawings (taper plus/minus) and how taper affects tolerance zones.
• Parting surfaces and surface mismatch (SMI): Requirements for indicating parting lines and evaluating surface mismatch between mating mould halves.
• Wall thickness and rejection criteria: Guidance on wall thickness considerations and when castings are to be rejected based on the specified tolerances.
• Drawing indications: How to reference the document and use general tolerancing in technical product documentation (title block or specific references).
• Informative annexes: Practical tables and explanatory annexes (e.g., Annex A on achievable tolerances by process, Annex B on machining allowances, Annex E examples of application).

Applications and users

Who uses ISO 8062-3:2023:

• Foundries and casting suppliers - to define producible tolerances and required machining stock.
• Design and R&D engineers - to specify realistic tolerances at the design stage that influence casting method and cost.
• Drawing authors and technical drafters - for consistent general tolerancing and taper/parting line notation on engineering drawings.
• Manufacturing and quality engineers / inspection - to establish acceptance/rejection criteria and inspection plans.
• Purchasers and contract manufacturers - to communicate clear tolerance and machining allowance expectations in purchase orders.

Practical uses:

• Selecting tolerance grades for individual features or general title-block tolerances.
• Determining required machining allowance and planning finishing operations.
• Coordinating part design with foundries to balance cost, manufacturability and function.

Related standards

• ISO 8062 series (Part 1 vocabulary; Part 2 application guidance)
• ISO/TS 8062-2 (delivery and application guidance)
• ISO 10135 (drawing indications for moulded parts)
• ISO 1101 / ISO 21920-1 (geometrical tolerancing)
• ISO 5459 (datums and datum systems)
• ISO 129-1 (presentation of dimensions and tolerances)

Keywords: ISO 8062-3:2023, geometrical product specifications, castings tolerances, machining allowances, draft angles, dimensional casting tolerance, GPS standard.