Introduction / Context:
GD&T uses geometric concepts to define allowable variations in manufactured parts. “Geometric” covers idealized elements—planes, cylinders, lines, points—and their relationships (orientation, location, runout), which are essential to how parts assemble and function.
Given Data / Assumptions:
- Features of size (holes, pins) and surfaces (faces) are modeled by geometric elements.
- Function requires controlling form (flatness, cylindricity) and relationships (position, perpendicularity).
- Datums define reference frames for measurement.
Concept / Approach:
The geometric controls in GD&T correspond to deviations from these ideal shapes and relationships. For instance, cylindricity limits how much a shaft can deviate from a perfect cylinder; position limits how far a hole axis may stray from its true location relative to datums.
Step-by-Step Solution:
Identify the geometric element that models the feature (plane, cylinder, line).Choose the control that protects function (e.g., flatness for sealing, perpendicularity for alignment).Apply datum references as needed to relate features consistently.Specify a tolerance zone that balances function and manufacturability.
Verification / Alternative check:
Use CMM simulation to confirm that the selected geometric control maintains assembly performance across variation.
Why Other Options Are Wrong:
Incorrect: “Geometric” is not a generic label; it specifically references ideal shapes and relationships.Refers only to square profiles / Limited to threads and gears: GD&T applies broadly to many shapes and features, not just a narrow subset.
Common Pitfalls:
Equating “geometric” with only size tolerances.Choosing inappropriate controls (e.g., straightness when flatness or profile is needed).
Final Answer:
Correct
Discussion & Comments