This class provides permissible deviations based on the nominal size of the dimension. Nominal Length Range (mm) Tolerance (± mm) over 3 to 6 over 6 to 30 over 30 to 120 over 120 to 400 over 400 to 1000 over 1000 to 2000 over 2000 to 4000 ISO 2768-1 Tolerance Chart ISO 2768-2: Geometrical Tolerances (Class K)
Despite its utility, 'mk' is not a universal solution. Do not rely on this standard in the following scenarios:
Therefore, when you see in a drawing title block, it means the component must be manufactured to Medium linear tolerances and Medium geometric tolerances . ISO 2768-m (Part 1): Linear and Angular Dimensions general tolerance iso 2768-mk
Before focusing on the "mk" classification, it is essential to understand the parent standard. ISO 2768 is an international standard titled "General tolerances for linear and angular dimensions without individual tolerance indications."
Provides a baseline for quality inspection across different suppliers and manufacturing facilities. General Tolerance - ISO 2768 1 & 2 - ZEISS Quality Forum This class provides permissible deviations based on the
| Standard | Description & Application | | :--- | :--- | | | The 'f' (fine) class for linear dimensions and 'H' class for geometry is significantly tighter than the mK combination. It is the standard choice for most CNC-machined metal parts, especially where precise mating features are critical. For example, for a dimension between 30 and 120 mm, ISO 2768-f would specify a tolerance of ±0.15 mm, while ISO 2768-m allows ±0.3 mm. | | ASME Y14.5 | This is the primary Geometric Dimensioning and Tolerancing (GD&T) standard in the United States. Unlike ISO 2768, which sets default general tolerances, ASME Y14.5 is a comprehensive system using a library of symbols to define specific geometric controls on a feature-by-feature basis. For parts being manufactured to US standards, ASME Y14.5 is the relevant framework. |
If a shaft length is specified as 50 mm with no individual tolerance, ISO 2768-mk permits a length between 49.7 mm and 50.3 mm. ISO 2768-m (Part 1): Linear and Angular Dimensions
ISO 2768 is an international standard that defines general tolerances for linear and angular dimensions, as well as geometric tolerances for features without individual tolerance indications. It simplifies technical drawings by eliminating the need to specify tolerances for every single dimension. is a combination of two parts of the standard:
| Range of Nominal Length (mm) | Straightness / Flatness (mm) | Perpendicularity (mm) | Symmetry (mm) | Runout (mm) | | --- | --- | --- | --- | --- | | 10 to 30 | 0.05 | 0.1 | 0.2 | 0.1 | | >30 to 100 | 0.1 | 0.2 | 0.3 | 0.2 | | >100 to 300 | 0.2 | 0.4 | 0.6 | 0.4 | | >300 to 1000 | 0.3 | 0.6 | 1.0 | 0.6 | | >1000 to 3000 | 0.4 | 0.8 | 1.5 | 0.8 |
Section D — Problem solving & design considerations (40 marks) 13. (10) You are designing a bracket with multiple features. Explain, with brief justification, which features you would: a) apply ISO 2768‑m to (3 examples), b) require specific tighter tolerances (3 examples), and c) select ISO 2768‑k for (2 examples). 14. (8) Calculate cumulative tolerance stack-up for three aligned features in series: A, B, and C, nominal lengths 15 mm, 25 mm, and 40 mm respectively, all unspecified on the drawing and ISO 2768‑m applies. Use the simplified table above to compute worst‑case total length tolerance and resulting possible total length range. 15. (8) For the same features as Q14 but B is specified with a tighter machining tolerance of ±0.05 mm (explicit), while A and C remain under ISO 2768‑m, compute the worst‑case total length range. 16. (6) Explain how note “ISO 2768‑m unless otherwise specified” can reduce drawing clutter but also identify two risks associated with relying on general tolerances. 17. (8) A customer requires interchangeable parts with consistent function across suppliers. Propose a concise set of drawing practices (6 actionable items) to ensure interchangeability while using ISO 2768‑m where appropriate.