Meaning
A combined international standard specifies general tolerances for linear and angular dimensions and for geometrical features on manufactured parts. The designation iso 2768-mk governs the allowable deviations for features that do not have their own individual tolerance on an engineering drawing. It measures the accuracy level by assigning a tolerance class for linear dimensions (m for medium) and a class for geometry (k).
This standard applies to the simplification of drawings for parts made by various processes, including plastic moulding. It stops applying when a specific dimension is given its own tolerance, which always takes precedence. Designers use this standard to define a baseline of quality that is achievable with standard workshop practices.
Tolerance Level
Selecting this specific classification indicates a requirement for a balanced level of precision that is neither too loose nor excessively tight. The iso 2768-mk group provides a range of allowable deviations based on the size of the dimension. For a linear dimension between thirty and one hundred and twenty millimeters, the medium class allows a deviation of plus or minus zero point three millimeters.
This level is generally suitable for the non-critical features of a plastic component. The geometric class k then defines the limits for flatness, symmetry and run-out. By citing this standard, the designer ensures that the part will have a professional finish and a consistent shape without the need for over-tolerancing.
This approach reduces the complexity of the drawing and the time required for inspection.
Production Baseline
Manufacturers use the general tolerances of the standard to set up their machines and plan their quality checks. When a drawing refers to iso 2768-mk, the moulder knows that the process must be stable enough to hold these standard limits. This involves maintaining consistent injection pressures and cooling cycles.
Because the tolerances are predefined, the moulder can quickly assess whether a new tool is capable of producing acceptable parts. If a feature consistently falls outside the general tolerance, it may indicate a problem with the mould design or the resin flow. The standard provides a common language between the designer and the manufacturer, reducing the risk of disputes over part quality.
It establishes a clear expectation for the quality of the work coming out of the factory.
Deviation Management
Handling parts that do not meet the general tolerances requires a clear understanding of the standard’s rules. If a non-toleranced dimension on a part exceeds the iso 2768-mk limits, the part is technically non-compliant. However, the manufacturer can still use the standard to determine how much the part must be corrected.
For plastic parts, some deviations might be acceptable if they do not affect the function or appearance of the item. In these cases, the designer may choose to override the general tolerance for that specific feature. Regular audits of the production line ensure that the parts continue to fall within the expected ranges.
This proactive management of deviations helps to keep the production costs low and the quality high. The standard acts as a safety net for the overall dimensional integrity of the project.
