Tolerance Stack up Analysis

Calculation Method

Worst case scenarios are evaluated by summing the maximum and minimum limits of every individual component in the chain. The tolerance stack up analysis often uses the root sum squares method to provide a more realistic statistical prediction of the variation. This statistical approach assumes that it is unlikely for every part in an assembly to be at its extreme limit simultaneously.

Designers use these results to adjust the nominal dimensions or tighten the tolerances of specific features.

Mechanical Reliability

Precise alignment of critical components depends on the outcome of this study during the design phase. If the tolerance stack up analysis reveals a high probability of failure, the engineer might change the assembly sequence or add shims to the design. This prevents costly rework or the scrapping of parts on the production line.

It is particularly important for high precision mechanisms like optical sensors or engine components.

Documentation Requirement

Quality control teams use the results of the study to define the inspection plan for incoming parts. The tolerance stack up analysis provides the justification for the choice of critical to quality dimensions that must be measured on every batch. It ensures that the manufacturing process is capable of producing parts that will fit together consistently.

This formal record remains a vital part of the technical data package for the life of the product.