The tolerance range for sand casting is primarily governed by international and national standards, which define systematic grades rather than a single universal value. The achievable tolerance depends heavily on the chosen grade, the specific dimension of the cast part, and the casting process details.
Here is a summary of the key international and national standards that specify these tolerances:
| Standard Number | Title (English) | Key Scope & Relevance |
| ISO 8062-3:2023 | Geometrical product specifications (GPS) – Dimensional and geometrical tolerances for moulded parts – Part 3: General dimensional and geometrical tolerances and machining allowances for castings | The primary international standard. It specifies tolerance grades for linear dimensions and geometric features (straightness, flatness, etc.) for castings in all metals. |
| GB/T 6414-2017 | Castings – Dimensional tolerances and geometrical tolerances and machining allowances | The previous Chinese national standard (in Chinese and English), functionally aligned with ISO. |
| 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 | The new Chinese national standard (in Chinese and English) effective Dec. 2025, replacing GB/T 6414-2017. |
📏 Understanding Tolerance Grades and Values
These standards use a tolerance grade system (typically designated as CT1, CT2, CT3… up to CT16). A lower CT number indicates a tighter, more precise tolerance.
Typical Sand Casting Grades: For conventional sand casting processes, the typical tolerance grades usually fall between CT8 and CT12, with CT9 to CT11 being very common. More advanced processes like 3D printed sand molds can achieve significantly tighter tolerances (e.g., CT4 to CT6).
How Tolerance Value is Determined: The actual tolerance value (in millimeters) is not a fixed number. It is determined by two factors:
The chosen CT grade.
The basic size of the dimension in question.
The standards provide detailed tables where you look up the basic size range and the CT grade to find the corresponding bilateral tolerance value (e.g., ±0.5 mm).
Example from Standards: For a casting dimension of 100 mm:
At CT10, the standard tolerance might be approximately ±0.9 mm.
At CT12, it would be wider, perhaps around ±1.5 mm.
