A tolerance establishes the permitted variation of a finished feature. Set it from the function of that feature and confirm it against the intended process. Applying the tightest available tolerance everywhere can increase cost without improving the product, while leaving a critical interface unspecified can create an avoidable fit or performance failure.
Distinguish nominal data from acceptance limits
CAD dimensions describe the intended geometry, but the drawing should identify the finished acceptance requirement where it matters. Clarify hole diameter after plating, finished board thickness and profile location. Use explicit units and datums so measurements are repeatable.
Review related variations together
Connector fit can depend on board thickness, hole position and component placement. Controlled impedance depends on a combination of conductor and dielectric dimensions. Evaluate the complete requirement instead of tightening one dimension while ignoring larger contributors.
Agree achievable process limits
Ask the fabricator and assembler to review the actual feature, material and construction. A tolerance quoted for one thickness or process may not apply elsewhere. Resolve exceptions before release and preserve the approved limits with the project documentation.
Choose a meaningful verification method
Define where and how a critical dimension is measured, the sampling plan and the required record. Consider the measurement capability and fixture influence. A nominally precise number is not useful if the inspection method cannot distinguish acceptable from unacceptable product reliably.
Release checklist
- State finished dimensions, units and datums.
- Tie tolerances to actual functional requirements.
- Review interacting variations across the assembly.
- Agree measurement, sampling and reporting.