10 Questions
What is concentricity in GD&T?
A 3-Dimensional cylindrical tolerance zone defined by a datum axis
What must be true for a cylindrical feature to meet the concentricity tolerance?
All median points along the entire feature must be within the tolerance zone
What is the primary purpose of position tolerances in GD&T?
To locate features from datums or establish coaxiality or symmetry
What does a position tolerance define?
The maximum allowable deviation from the true position of a feature
What is the 'true position' in GD&T?
The theoretically exact position of the feature
What is symmetry in GD&T?
A condition where the median points of opposed feature surfaces are coincident with a datum axis or center plane
If a feature meets the symmetry tolerance, what can be inferred?
The opposed elements of the feature are aligned with the datum axis or plane
What is the relationship between concentricity and symmetry tolerances?
Concentricity controls circularity, symmetry controls opposed element alignment
If a position tolerance is given, what does it NOT control?
Size of the feature
What tolerance would be used to ensure two holes are coaxial?
Position
Study Notes
Geometric Dimensioning and Tolerancing (GD&T)
Form and Profile Controls
- 14 characteristics that may be controlled, including:
- Flatness
- Straightness
- Circularity
- Cylindricity
- Line Profile
- Surface Profile
Form Controls
- Flatness: a perfectly flat surface must contain all elements in one plane
- Straightness: an element of a surface or an axis is a straight line
- Circularity (roundness): all points of the surface intersected by any plane perpendicular to a common axis are equidistant from the axis
- Cylindricity: controls the surface of a cylinder, including parallelism of the sides
Profile Controls
- Line Profile: controls single line elements on a feature, each element is independent of all others
- Surface Profile: controls all elements on a feature, simplest level of control, controls form only
Orientation, Runout, and Location Controls
- 14 characteristics that may be controlled, including:
- Perpendicularity
- Angularity
- Circular Runout
- Total Runout
- Concentricity
- Position
- Symmetry
Orientation Controls
- Perpendicularity: two parallel planes of cylindrical zones that are perpendicular to a datum plane
- Angularity: a surface, center-plane or axis at a specified angle (other than 90°) form a datum plane or axis
- Parallelism: two parallel planes of cylindrical zones that are parallel to a datum plane
Runout Controls
- Circular Runout: controls circularity and concentricity, measured by rotating the part 360°
- Total Runout: controls cumulative variations of circularity, straightness, coaxiality, angularity, taper, and profile of a surface
Location Controls
- Concentricity: a 3-Dimensional cylindrical tolerance zone defined by a datum axis
- Position: locates features from datum’s or establishes coaxiality or symmetry
- Symmetry: median points of all opposed or correspondingly-located elements of two or more feature surfaces are coincident with the axis or center plane of a datum feature
Test your knowledge of Geometric Dimensioning & Tolerancing (GD&T) concepts with this quiz. Explore topics such as form, profile, characteristic controls, feature types, and tolerance symbols.
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