Introduction / Context:
Geometric dimensioning and tolerancing (GD&T) supplements size limits by controlling shape and spatial relationships. Symbols such as flatness, perpendicularity, position, and total runout specify how far a real feature may deviate from the theoretically exact geometry and datum references shown on the drawing.
Given Data / Assumptions:
- Features of size and datums are identified on the drawing.
- Functional relationships (e.g., coaxiality, perpendicularity) matter to assembly performance.
- Inspection methods (CMM, gauges) are available to verify geometric controls.
Concept / Approach:
Geometric tolerance zones (planes, cylinders, boundaries) bound allowable deviation of form and position. For example, a position tolerance limits how far a hole's axis may wander from its true position while still ensuring assembly with a mating pin. This framework protects function with fewer overly tight size limits.
Step-by-Step Solution:
Identify critical features and their functional datums.Select appropriate geometric controls (e.g., flatness for sealing surfaces, position for holes).Define tolerance zone size and material condition modifiers (e.g., MMC) when beneficial.Specify inspection plan capable of validating the geometric requirement.
Verification / Alternative check:
Perform an assembly tolerance study to verify that the GD&T scheme ensures fit and function at worst case.
Why Other Options Are Wrong:
Incorrect: Misstates the purpose of geometric tolerances.Applies only to surface roughness / Used only for castings: GD&T is independent of surface finish and applies to all manufacturing processes.
Common Pitfalls:
Using size tolerances to control relationships better handled by GD&T.Omitting datum references, making geometric controls ambiguous.
Final Answer:
Correct
Discussion & Comments