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In CNC machining ISO-2768 standardizes tolerances in order to guarantee quality and precision during manufacturing. This standard helps manufacturers and engineers to improve product reliability, reduce costs and streamline processes as well. That’s why in this blogpost we will cover ISO 2768 standards for linear, angular and geometric tolerances and their significance in manufacturing.
What is ISO 2768?
ISO 2768 is international standard in manufacturing that describes general tolerances for linear and angular dimensions as well as for geometrical features. This not only eliminates the need to specify tolerances on technical drawings for each dimension but also greatly simplifies the production procedures and design. Apart from that, this standard guarantees compatibility and dimensional accuracy in different production processes like CNC machining, sheet metal fabrication and injection molding.
ISO 2768-1
ISO 2768-1 sets general tolerances for linear and angular dimensions. Such dimensions are diameters, lengths, radii, angles and chamfer heights. According to the standard, tolerances are classified into four types, such as
Fine (f): It is the highest precision level.
Medium (m): represents balance between manufacturability and precision.
Coarse (c): It is suitable for less critical parts and permits larger deviations.
Very Coarse (v): The least stringent class which is perfect for non critical dimensions.
Linear Dimensions
Internal sizes, step sizes, distances and external sizes are all linear dimensions. Each tolerance class based on nominal ranges specifies permissible deviations.
Below you can see a table of nominal sizes and tolerance classes as per ISO 2768-1.
| Nominal Size Range (mm) | Fine (f) ± (mm) | Medium (m) ± (mm) | Coarse (c) ± (mm) | Very Coarse (v) ± (mm) |
|---|---|---|---|---|
| 0.5 to 3 | 0.05 | 0.1 | 0.2 | – |
| 3 to 6 | 0.05 | 0.1 | 0.3 | 0.5 |
| 6 to 30 | 0.1 | 0.2 | 0.5 | 1.0 |
| 30 to 120 | 0.15 | 0.3 | 0.8 | 1.5 |
| 120 to 400 | 0.2 | 0.5 | 1.2 | 2.5 |
| 400 to 1000 | 0.3 | 0.8 | 2.0 | 4.0 |
| 1000 to 2000 | 0.5 | 1.2 | 3.0 | 6.0 |
The permissible deviations also widen as nominal size increases. For example, in the medium class the deviations vary from ±0.1 mm for sizes up to 6 mm to ±1.2 mm for sizes from 1000 to 2000 mm.
Angular Dimensions
Angular dimensions include chamfers, angles as well as other angular features. Each tolerance class defines permissible deviations similar to linear dimensions. But in the case of angular dimensions, the deviations are usually expressed in arc minutes or degrees.
Following is table of tolerance classes based on nominal sizes for angular dimensions per ISO 2768-1.
| Nominal Size Range (mm) | Fine (f) ± | Medium (m) ± | Coarse (c) ± | Very Coarse (v) ± |
|---|---|---|---|---|
| Up to 10 | ±1° | ±1° | ±1°30′ | ±3° |
| 10 to 50 | ±30′ | ±30′ | ±1° | ±2° |
| 50 to 120 | ±20′ | ±20′ | ±30′ | ±1° |
| 120 to 400 | ±10′ | ±10′ | ±15′ | ±30′ |
| 400 | ±5′ | ±5′ | ±10′ | ±20′ |
For all sizes, permissible deviations for angular dimensions are specified under each tolerance class. For instance, in the case of the fine class, the deviation for all angular dimensions is ±1° and then for the very coarse class, the deviation increases to ±3°.
ISO 2768-2
ISO 2768-2 defines general geometrical tolerances in terms of form and positional tolerance for features. This standard is intended primarily for parts produced by material removal processes such as CNC machining. It defines tolerances in three precision classes—H (high precision), K (medium precision) and L (low precision).
Orientation, location, runout and shape of a part or feature are controlled by geometric tolerances. They tell how position of a feature can deviate from its intended or ideal form and how a feature is formed. They are used for more complicated geometric aspects of a part, such as straightness, flatness, circularity, perpendicularity, symmetry etc.
Form Tolerances
The shape of individual features and how much a part can deviate from its ideal shape are controlled by form tolerances. Straightness and flatness are included among these geometric tolerances. Straightness makes sure that as a feature deviates from an ideal straight line only within allowed limits and flatness is the allowable variation in a surface’s flatness.
General tolerances on straightness and flatness
| Nominal Length (mm) | H (mm) | K (mm) | L (mm) |
|---|---|---|---|
| Up to 10 | 0.02 | 0.05 | 0.1 |
| 10 to 30 | 0.05 | 0.1 | 0.2 |
| 30 to 100 | 0.1 | 0.2 | 0.4 |
| 100 to 300 | 0.2 | 0.4 | 0.8 |
| 300 to 1000 | 0.3 | 0.6 | 1.2 |
| 1000 to 3000 | 0.4 | 0.8 | 1.6 |
Orientation Tolerances
Orientation tolerances control alignment of features with respect to each other. They are used to make sure that a certain feature of a part is properly orientated to datum points or other features. This includes angularity and perpendicularity.
Deviation from a right angle is controlled by perpendicularity whereas deviation from specified angles other than 90° is controlled by angularity.
General tolerances on perpendicularity
| Nominal Length (mm) | H (mm) | K (mm) | L (mm) |
|---|---|---|---|
| Up to 100 | 0.2 | 0.4 | 0.6 |
| 100 to 300 | 0.3 | 0.6 | 1 |
| 300 to 1000 | 0.4 | 0.8 | 1.5 |
| 1000 to 3000 | 0.5 | 1 | 2 |
Positional Tolerances
Positional tolerances specify the allowable deviation in position of feature (between its actual and intended position on a part) such as slot, pin or hole. These are the tolerances which guarantee that centers, holes or other features are located correctly so that they fit together properly in assembly. This includes symmetry and run out.
Deviations from a central axis or a plane are controlled by symmetry while run out limits variations of a part rotating around reference axis.
General tolerances on Symmetry and Run out
| Nominal Length (mm) | L (mm) | K (mm) | H (mm) |
|---|---|---|---|
| Up to 100 | 0.6 | 0.6 | 0.5 |
| 100 to 300 | 1 | 0.6 | 0.5 |
| 300 to 1000 | 1.5 | 0.8 | 0.5 |
| 1000 to 3000 | 2 | 1 | 0.5 |
Importance of ISO 2768 Tolerance in Manufacturing
Technical Drawings
ISO 2768 eliminates the need to specify tolerances for every individual dimension which simplifies technical drawings. On the drawing, the engineers can directly indicate a general tolerance class like ISO 2768-m. It minimizes errors, reduces complexity and speeds up the design to production process.
Better Efficiency
ISO 2768 reduces the production time by simplifying the production process. It removes the need to specify tolerances at each feature and thereby decreases manufacturing errors and design complexity. Moreover this standardized approach speeds up production cycles and guarantees consistent quality across components which in turn saves both resources and time.
Interoperability
ISO 2768 standardizes tolerances in order to improve interoperability by assuring that parts produced in different locations will fit together in assemblies. Such global compatibility simplifies supply chain integration, minimizes discrepancies and supports collaboration amongst designers, suppliers and manufacturers across industries such as automotive, electronics and aerospace.
Global Collaboration
by standardizing tolerance, ISO 2768 promotes global cooperation. It permits providers from different areas to work together with no problems. This universal framework not only mitigates ambiguity but also guarantees compatibility across borders. Besides that it supports the international supply chain which makes it important in modern manufacturing industries.
To Sum Up
ISO 2768 is important standard which makes the tolerance in linear, angular and geometrical dimensions quite simplified. This standard assures that parts manufactured by different manufacturers are compatible as well as interchangeable.
If you require any kind of CNC machining, injection molding and sheet metal fabrication services with ISO 2768 standards, then RICHCONN is best option. You can contact us at any time.
Related Questions
What is ISO 2768 mk meaning?
ISO 2768-mk includes medium (m) tolerances for linear dimensions and general geometrical tolerance class K. It guarantees balanced precision in manufacturing for both dimensional and geometric features.
What is ISO 2768-fk?
ISO 2768-fk defines fine (f) tolerance for linear dimensions and geometrical tolerance class K. It is for high precision components in which tight geometric and dimensional accuracy is required.
How does ISO 2768 differ from ISO 286?
ISO 2768 specifies general tolerances for geometry and dimensions whereas ISO 286 uses system of limits and fits to provide fits and tolerances for shafts and holes.
Can ISO 2768 be used for 3D-printed parts?
Yes ISO 2768 is applicable to 3D printed parts. But additional consideration may be required because of layer based manufacturing and distinct material properties.
Which industries use ISO 2768 the most?
ISO 2768 is used in industries like automotive, aerospace, medical devices and CNC machining frequently to assure precision as well as compatibility in components manufacturing.
