symbols are used to define the relationships between a part
features and measurement references.
Straightness control of a feature in GD&T can be surface
Straightness or an axis Straightness of a cylinder. This
is usually called out with an maximum material condition.
Flatness is a common symbol that references how flat a
surface is regardless of any other datums or features.
circularity also called roundness. This symbol is used
to describe the required roundness of an object.
Cylindricity symbol is used to describe an object conforms
to a cylinder axis. a cylindrical feature to ensure that
it is round enough and straight enough along its axis.
Profile of a Line Profile
of a line describes a tolerance zone around any curved
profile or shape. It is usually called out on a profile
surface, like a radius on a part, it specify how much
that cross-section could vary from a true curved radius.
Profile of a Surface Profile
of a surface is similar to the Profile of line, but it
controls the entire 3-Dimensional tolerance zone around
a surface, the entire surface has to fall within the tolerance
is the symbol that control orientation of one feature
to another at a referenced angle.
is a tolerance that controls Perpendicularly between two
90° surfaces, or between a surface and hole axis.
is a tolerance that controls parallelism between two surfaces
is the most commonly used symbol in GD&T, The True
Position is the exact coordinate, or location allowable
in the defined dimensions.
is a tolerance that controls the central axis of the referenced
feature, to a datum axis.
is the tolerance that is used to ensure two features on
a part are uniform across a datum plane.
Circular runout Runout
is the total variation that the reference surface can
have when the part is rotated around the datum axis.
Total runout Total
Runout controls the value of a feature when the feature
is rotated around the datum axis and along the axis. Both
radial variation and axial variation are measured within
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