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Importance of GD&T for Design, Manufacturing, and Quality


Applied GD&T importance of

Whether your company is a part of the design process or manufacturing or quality, GD&T competency is critical for success.  Regardless of what part of the process you are in, Applied GD&T can help you move forward with a successful implementation of Geometric Dimensioning & Tolerancing.

If you are in design, it's critical that you have a deep enough understanding to properly apply datums and tolerances that reflect the function of the part (while also considering current manufacturing and inspection capabilities). If you are a supplier in manufacturing or quality, I would argue that there is an even greater need to have a broad understanding of GD&T. Read on for more...


If you control the design process, you need to have the knowledge of GD&T to apply datums and tolerancing that accurately reflect the function of the part. A lack of competence in design often leads to tolerancing that does not reflect the function of the part. This may lead to accepting bad parts and rejecting good parts. Also, when a designer/design team lacks an adequate competency in GD&T, oftentimes tolerances are needlessly tightened hoping that it will increase the likelihood of getting functional parts. In both scenarios, cost implications are obvious (and not-so-obvious).

When the GD&T does not correctly convey the function of the part, it cannot be manufactured and inspected with the assurance that conformance to the design equals a functional part. It may be an obvious statement, but for these reasons, it is critical that designers have a good working knowledge of GD&T and how to apply it optimally.


Those in manufacturing need to make parts that conform to the GD&T (at competitive prices and turn-around time). Not understanding GD&T hinders you from being competitive and leads to less profit and more scrap. Properly understanding GD&T will enable you to estimate more accurately, and to establish a manufacturing process that is optimal from the start and that will minimize rejected parts. Again, as with design, there are obvious cost implications to poor GD&T competency in manufacturing.


For the full implementation of GD&T to be successful, we need to determine whether a part actually conforms to the design drawing. That's where quality/inspection comes in. If those in quality/inspection don't understand GD&T (and the proper techniques for evaluating GD&T), the implementation will obviously fail. Understanding how datums constrain degrees of freedom, how features of size are calculated, the rule of simultaneity, and how to report the results clearly are critical concepts for those in dimensional inspection. As with poor design, poor inspection will likely result in rejecting good parts and accepting bad parts.


The reality is that there are various "philosophies" of GD&T that are applied in different organizations and industries. Therefore, as a manufacturing or quality supplier, it's critical to have competency in the full breadth of the GD&T standard and how your customer may be applying it. It's also important to be know the difference between invalid GD&T and non-optimal GD&T. Both are issues but need to be handled differently. In light of that, it is critical to be able to intelligently communicate with the customer when there are legitimate issues with the GD&T on the print. It's never a fun scenario when you go to confront your customer about their crazy GD&T only to find out that the problem is actually a lack of understanding on your part. I know I've been there;)

Good Training is Key

Whether your starting from scratch or looking to fill in some gaps in your GD&T competency, Applied GD&T is here to come alongside you to help you and your team move forward. Contact me for more information.

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