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Two parts can each be “within tolerance” and still fail to assemble. That is why tolerance stack-up analysis matters. The goal is to understand how individual dimensional variations combine in the final assembly.
Start With the Functional Requirement
Do not begin by adding every dimension on the drawing. Start with the gap, alignment or movement that actually matters to the product.
Build the Tolerance Chain
Trace the dimensions that physically influence the requirement. Keep the chain short and use the actual manufacturing dimensions rather than unrelated CAD measurements.
Worst Case vs Statistical Thinking
Worst-case analysis assumes all dimensions reach their limiting conditions together. Statistical methods consider variation distributions and may predict a different assembly result. The appropriate method depends on the product and quality requirements.
Where Designers Go Wrong
A common mistake is tightening every tolerance instead of understanding the stack. That can increase manufacturing cost without solving the real problem.
Better Design
Use datums, functional dimensions and robust locating features to reduce unnecessary variation. Good tolerance analysis is often a design improvement exercise, not just a calculation.
Keep learning: Explore more practical engineering articles in the GetCADFile Design Guide.