When to Use GD&T

In this Question Line video, Jason discusses the following question and explains when to use GD&T:

I understand the difference between basic dimensions and geometric dimensions, but I am curious how you decide what features should have basic vs geometric dimensions. In the typical case shown of a square block with 4 holes in it, how is it decided to basic dimension the hole locations and geometric dimension the size of the block? Is it based on criticality of the feature, does it have to do with relating back to a datum feature, or something else entirely?

Jason discusses the below drawing referenced in the submitted question:

In this video, Jason explains the difference between locating features using GD&T and doing so with traditional coordinate dimensions. He clarifies that the +/- toleranced dimensions on GD&T drawings, like that above, are size dimensions and are not used for locating features. Therefore, he rewords the above question to answer when and how Geometric Dimensioning and Tolerancing should be used, and walks through a second drawing in explanation.

Looking for answers to your GD&T questions? Submit your question to our GD&T experts at the link below! 

https://www.gdandtbasics.com/share-your-gdt-questions/

If your question is selected, we will notify you when our video answer is posted to our YouTube channel.

* If you are a current student, reach out to us directly and we will get you into contact with your instructor. Active students’ questions receive a direct response within 24-48 hours.