Straightness : GD&T Tips SMLease Design

Straightness tolerance in GD&T, controls a condition where all element of a surface or an axis lies in a straight line.

Application of Straightness

  • To control the foam of a line on the surface / feature
  • Straightness of an axis

Note : Datum plane is not required to define straightness and to define axis straightness LMC and MMC modifiers can be used.

1. Surface Straightness

Surface straightness is a 2-Dimensional tolerance used to ensure, a part is uniform across a surface or feature. It can be applied to a flat surface of a cylinder or block

Representation Of Surface Straightness

Tolerance Zone For Surface Straightness

Tolerance Zone will be 2 parallel lines 0.1 mm apart in 2D Plane

Measurement Of Surface Straightness

For surface straightness measurement, Dial gauge is fixed and part is moved over the surface plate . Variation observed in the reading of dial gauge is the value of straightness tolerance.

2. 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.
Axis Straightness tolerance makes a 3D tolerance zone. It helps in controlling the bending or twisting of a part. LMC and MMC modifiers can be used with straightness axis tolerance.

Representation Of Surface Straightness

Tolerance Zone for straightness of an Axis

Tolerance Zone will be a cylindrical boundary around the true central axis of the part.

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