Straightness is a type of foam control tolerance in GD&T. It controls a condition where all element of a surface or an axis lies in a straight line. Datum plane is not required to define straightness. LMC and MMC modifiers can be used to define straightness of an axis. It can defined to control the line on surface or feature or an axis.
It creates a 2-Dimensional tolerance zone and ensures the part is uniform across a surface or feature. It can be applied to a flat surface of a cylinder or block.
Datum plane is not required to define surface straightness.
Tolerance Zone will be two parallel lines equally apart by a distance equal tolerance value, from controlled surface in 2D Plane.
To measure straightness of a surface, Dial gauge is fixed and part is moved over the surface plate.
Straightness tolerance value will be equal to variation observed in dial gauge reading.
Straightness of an Axis
Straightness of an axis controls the central axis of any part. It defines how the axis of any part can deviate from straightness.
Datum plane is not required to define straightness of an axis. LMC and MMC modifiers can be used with straightness axis tolerance.
Axis Straightness tolerance creates a 3D tolerance zone. It helps in controlling the bending or twisting of a part. Tolerance Zone will be a cylindrical boundary around the true central axis of the part.
To sum up, Straightness is a type of foam control tolerance in GD&T. It controls a condition where all element of a surface or an axis lies in a straight line.
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