Straightness Tolerance : GD&T Basics

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.

You can refer this article to understand the basics of geometric tolerance.

Surface Straightness

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.

Representation

Datum plane is not required to define surface straightness.

Tolerance Zone

Tolerance Zone will be two parallel lines equally apart by a distance equal tolerance value, from controlled surface in 2D Plane.

Measurement

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.

Representation

Datum plane is not required to define straightness of an axis. LMC and MMC modifiers can be used with straightness axis tolerance.

Tolerance Zone

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.

Conclusion

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.

Got Question?  We will be happy to help.

If you think we missed Something?  You can add to this article by sending message in comment box. We will do our best to add it in this post.

Add a Comment

Your email address will not be published. Required fields are marked *