Saturday, September 23, 2023

# GD &T Definitions

GD &T Definitions

Flatness: It defines how much a surface can vary from its perfect plane.

Straightness:It defines how much a line element can vary from a straight line.

Circularity:It defines how much circular element can vary from a perfect circle.

Cylindricity:It defines how much surface can vary from a perfect cylinder.

Perpendicularity: It is the condition that results when a surface, axis or center plane is exactly 90° to a datum.

Angularity: It is the condition of a surface, center plane or axis at a specified angle.

Parallelism: It is the condition that results when a surface, center plane or axis is exactly parallel to a datum.

Position: True position is the theoretically exact location of a FOS as defined by basic dimensions.

Concentricity: It is the condition where the median points of all diametrically opposed elements of a cylinder (radially disposed features like a hexagon or a surface of revolution) are congruent with axis of a datum feature. A median point is the mid-point of a two-point measurement.

Symmetry: Symmetry is similar to concentricity. The only difference is that, while concentricity is used on surface of revolution, symmetry is used on planar features of size. Symmetry is the condition where the median points of all opposed elements of a feature of size are congruent with the center plane of a datum feature.

Circular runout: It is the composite control that affects the form, orientation and location of a circular element of a part feature relative to a datum axis.
Total runout: It is composite control that affects the form, orientation and location of all surfaces relative to a datum axis.

Least Material Condition (LMC): The condition where a feature of size contains the least amount of material within the stated limits of size.

Ex: maximum hole diameter and minimum shaft diameter.

Maximum Material Condition (MMC): The condition where the feature of size contains the maximum amount of material permitted within the stated limits of size.

Ex: minimum hole diameter and maximum shaft diameter.