Parallelism Tolerance : GD&T Basics

Parallelism is a type of orientation control tolerance. It controls parallelism between two lines, surfaces or axis. It does not control the angle of the referenced feature. But it creates a tolerance zone where all points of the feature must lie. 

Read this article to understand the basics of geometric tolerance.

Tolerance Representation

Surface or axis datum is required to represent parallelism Tolerance.

MMC and LMC conditions are also applicable with parallelism tolerance.

Tolerance Zone

Parallelism tolerance can be applied to surface or an axis. When it is applied to a surface it controls the parallelism between two planes. Whereas when it is applied to an axis. It controls how much parallel an axis is w.r.t. reference plane. 

Tolerance zone will be two parallel planes that are parallel to the datum feature or surface. All points on the controlled surface must lie within these parallel planes.

Application

Parallelism Tolerance ensures two surfaces are in synchronized with each other. And constant distance between them is maintained. It also avoids taper in any slot or cylindrical hole.

Measurement

Dial Gauge can be used to measure the parallelism tolerance of a part with respect to datum plane. 

For measurements, part is constrained w.r.t datum plane and gauge is moved across reference surface.

Conclusion

To sum up, Parallelism tolerance is a type of orientation control tolerance.It can be represented with surface or axis as datum.

Got Questions?  We will be happy to help.

If you think we missed Something?  You can add to this article by sending message in the 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Your email address will not be published.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 *