Tolerance is an essential concept in engineering, manufacturing, precision cnc machining and quality control,refers to the allowable variation or deviation from a specified dimension, value, or characteristic in a manufacturing or design process,to ensure the proper fit, function, and interchangeability of components and products. Here we introduce ISO 2768 standard and ISO 2768 tolerance chart.
What is ISO 2768?
ISO 2768 is an international standard that provides general tolerances for linear and angular dimensions without individual tolerance indications. It specifies tolerances for the dimensions of linear and angular sizes, as well as for form and position.
ISO 2768 is part of the ISO 2768 series, which includes different parts for different tolerance classes. The parts of ISO 2768 are as follows:
- ISO 2768-1: General tolerances for linear and angular dimensions without individual tolerance indications. It provides tolerance values for the dimensions of lengths, widths, heights, angles, and other linear and angular dimensions.
- ISO 2768-2: Geometrical tolerances for features without individual tolerance indications. It provides tolerance values for the form and position of features such as straightness, flatness, circularity, cylindricity, and profile of a surface.
The tolerances specified in ISO 2768 are intended for general engineering applications where no specific tolerance requirements are given. They provide a standardized set of tolerances that can be used as a starting point when no other requirements are specified or when a general level of tolerance is acceptable.
It’s important to note that ISO 2768 is not intended for critical or high-precision applications where tighter tolerances are required. In such cases, more specific and tighter tolerances should be defined based on the specific requirements of the application.
ISO 2768 provides a common reference for tolerances and helps ensure consistency and interchangeability of manufactured parts across different industries and countries. It simplifies the process of specifying tolerances in technical drawings and promotes international standardization and understanding.
What is ISO 2768-mK Meaning?
ISO 2768-mK is a part of the ISO 2768 standard that specifies a medium tolerance class for linear and angular dimensions with individual tolerance indications. The “mK” in ISO 2768-mK stands for “medium tolerance class with a guarantee of production process capability.”
ISO 2768-mK is used when more specific and tighter tolerances are required compared to the general tolerances provided in ISO 2768-1. It provides a higher level of precision and control over the manufacturing process.
In ISO 2768-mK, the tolerance values for individual dimensions are specified directly on the technical drawing using appropriate symbols and tolerance indications. These tolerance values are based on the specific requirements of the part and are typically tighter than the general tolerances specified in ISO 2768-1.
ISO 2768-mK takes into account the production process capability, meaning that it considers the capabilities of the manufacturing process and ensures that the specified tolerances can be consistently achieved during production.
The use of ISO 2768-mK allows for more precise and accurate dimensioning and tolerancing, which is particularly important for applications that require higher precision, tight fits, or critical functionality.
It’s worth noting that ISO 2768-mK is just one of the tolerance classes specified in ISO 2768, and different tolerance classes may be used depending on the specific requirements and level of precision needed for the part or assembly.
Which Tolerance to Choose?
You can determine the tolerance class based on the production capacity of the manufacturer and the requirements of the parts to be made. Usually, ISO 2768–fH is ideal for CNC machining.
Scope of ISO 2768-1 (General Tolerances for Linear and Angular Dimensions)
The scope of ISO 2768-1, titled “General tolerances for linear and angular dimensions,” is to provide a standardized set of general tolerances for linear and angular dimensions without individual tolerance indications. It covers a wide range of dimensions and features commonly found in engineering drawings and technical specifications.
ISO 2768-1 specifies tolerances for the following linear and angular dimensions:
- Length, width, and height dimensions
- External and internal diameters
- Straightness and flatness
- Perpendicularity and parallelism
- Symmetry and concentricity
- Angular dimensions and angles of inclination
- Positional tolerances
The standard provides tolerance values for these dimensions and features based on the size range of the dimension. The tolerance values are given as a range or limit, typically expressed in units of length or angle, such as millimeters (mm) or degrees (°).
ISO 2768-1 is intended to be used when no specific tolerance requirements are given for a particular dimension or feature. It provides a set of default tolerances that can be applied to engineering drawings and technical specifications as a starting point when no other requirements are specified or when a general level of tolerance is acceptable.
However, it’s important to note that ISO 2768-1 is a general standard and may not be suitable for all applications, especially those with higher precision requirements or critical functional needs. In such cases, more specific and tighter tolerances should be defined based on the specific requirements of the application.
ISO 2768-1 promotes standardization and uniformity in tolerancing practices across different industries and countries, simplifying the process of specifying tolerances for common dimensions and features.
ISO 2768 Tolerance Chart – ISO 2768 T1
Check out the ISO 2768 tolerance tables corresponding to the 4 classes. Please note that all tolerance in ISO 2768 is given in mm (Metric).
- Table 1: Permissible deviations for linear dimensions except for broken edges
- Table 2: Permissible deviations for broken edges (external radii and chamfer heights)
- Table 3: Permissible deviations of angular dimensions
1.General Tolerance Chart 1 – Linear Dimensions
| Tolerance Class | Tolerance Range |
|---|---|
| IT01 | ±0.025 |
| IT0 | ±0.04 |
| IT1 | ±0.1 |
| IT2 | ±0.2 |
| IT3 | ±0.4 |
| IT4 | ±0.8 |
| IT5 | ±1.6 |
| IT6 | ±3.2 |
| IT7 | ±6.3 |
| IT8 | ±12.5 |
| IT9 | ±25 |
| IT10 | ±50 |
| IT11 | ±100 |
| IT12 | ±200 |
2.General Tolerance Chart 2 – External Radius and Chamfer Heights
| Tolerance Class | Tolerance Range |
|---|---|
| IT0 | ±0.1 |
| IT1 | ±0.2 |
| IT2 | ±0.3 |
| IT3 | ±0.5 |
| IT4 | ±0.8 |
| IT5 | ±1.6 |
| IT6 | ±3.2 |
| IT7 | ±6.3 |
| IT8 | ±12.5 |
| IT9 | ±25 |
| IT10 | ±50 |
| IT11 | ±100 |
| IT12 | ±200 |
3.General Tolerance Chart 3 – Angular Dimensions
| Tolerance Class | Tolerance Range |
|---|---|
| IT0 | ±0.05 |
| IT1 | ±0.1 |
| IT2 | ±0.2 |
| IT3 | ±0.3 |
| IT4 | ±0.5 |
| IT5 | ±1 |
| IT6 | ±2 |
| IT7 | ±4 |
| IT8 | ±8 |
| IT9 | ±16 |
| IT10 | ±32 |
| IT11 | ±64 |
| IT12 | ±128 |
General Tolerances for Form and Position (DIN ISO 2768 T2)
1.Straightness and Flatness
| Tolerance Class | Tolerance Range |
|---|---|
| IT0 | 0.02 |
| IT1 | 0.04 |
| IT2 | 0.08 |
| IT3 | 0.15 |
| IT4 | 0.3 |
| IT5 | 0.6 |
| IT6 | 1.2 |
| IT7 | 2.5 |
| IT8 | 5 |
| IT9 | 10 |
| IT10 | 20 |
| IT11 | 40 |
| IT12 | 80 |
2.Symmetry (Position for ISO G&T Standard not ASME or ANSI GD&T)
The ISO standard does not specifically provide a tolerance chart for symmetry. However, symmetry can be considered as part of the positional tolerance in ISO Geometric Dimensioning and Tolerancing (GD&T) standards.
In ISO GD&T, positional tolerance is used to control the location and orientation of features relative to a datum reference frame. It specifies the allowable deviation from the perfect position of a feature. The positional tolerance can be applied to control symmetry by specifying the symmetry requirement in terms of the position tolerance zone.
The position tolerance zone consists of a cylindrical or rectangular boundary that defines the acceptable range for the location and orientation of the feature. By specifying the appropriate positional tolerance value, symmetry requirements can be controlled within the given tolerance zone.
For precise symmetry requirements, it is recommended to consult the specific ISO GD&T standards, such as ISO 1101, and work with design and engineering professionals who are familiar with the ISO GD&T system. They can provide guidance on the appropriate positional tolerance values and application of symmetry controls for your specific design requirements.