Introduction / Context:
Tolerancing is the bridge between design intent and manufacturability. Engineers select specific dimensional and geometric tolerances so that parts assemble and function as intended across real-world variation. The claim that tolerances are based on the part's function and fit is a foundational principle in GD&T and traditional limit-dimensioning.
Given Data / Assumptions:
- The part must mate with other components in an assembly.
- Functional performance, safety, and durability are primary goals.
- Manufacturing capability and inspection method influence feasible tolerances.
Concept / Approach:
Functional dimensioning assigns tolerances that guarantee performance. Fit classes (clearance, transition, interference) define how shafts, holes, bearings, and fasteners interact. Geometric controls (flatness, perpendicularity, position) manage form and location so assemblies work despite variation. Cost rises as tolerances tighten; therefore, designers choose the loosest tolerances that still satisfy function and fit.
Step-by-Step Solution:
Identify critical interfaces (e.g., hole–shaft, seal–bore) and define the required fit type.Translate functional needs into size limits (upper/lower) and geometric controls (e.g., position at MMC).Check manufacturing process capability; adjust tolerances to match proven capability while preserving function.Define inspection strategy to verify that the assigned tolerances can be measured reliably.
Verification / Alternative check:
Run a tolerance stack-up on the assembly to confirm that all worst-case combinations still meet the functional requirement.
Why Other Options Are Wrong:
Incorrect: Ignores the core purpose of tolerancing—ensuring function and fit under variation.Applies only to aerospace parts / Used only for threads and shafts: Functional tolerancing applies to all industries and components, not a limited subset.
Common Pitfalls:
Overtightening tolerances without functional justification, driving cost needlessly.Omitting geometric controls and relying only on size limits, which may not protect functional relationships.
Final Answer:
Correct
Discussion & Comments