Geometric Dimensioning and Tolerancing (GD&T) is used on engineering drawings and 3D models to unambiguously communicate acceptable limits of geometric variation for a part to function in the product(s) where it’s used. GD&T is a language, and like most languages, it may seem complex when first learning to read and write it. The requirements GD&T defines depend upon the context in which it is applied. Everyone using a drawing or some representation of an annotated 3D model – design, manufacturing, inspection, supply chain, etc. – must achieve a common understanding about the information it intends to convey. If the written specifications contain errors, the rest of the organization will struggle to understand the intent.
Many organizations perceive standardizing on the language of GD&T isn’t worth the investment, but their return-on-investment (ROI) evaluations often overlook the hidden costs of ambiguous requirements resulting from using only traditional +/- tolerances on their drawings. Not using GD&T forces manufacturing and inspection personnel to guess what the drawing specifications mean. Hoping that downstream personnel guess correctly is not an acceptable business strategy. Management should ensure that any designs released for production have tolerances determined and documented to ensure their products assemble and perform as expected by customers. If not, problems only become more expensive to resolve the later they are found.
Sigmetrix is dedicated to help everyone in the design, manufacture, and inspection groups understand the language of GD&T, and its application, through our series of courses. Realize, though, that training is just the first step in getting the full benefits GD&T has to offer. Sigmetrix personnel, with many years of practical experience in a variety of industries, are also dedicated to helping your employees transition the concepts from the classroom to your production environment. GD&T doesn’t have to be applied in a complicated manner, nor should it be. Our goal is to help your personnel find the optimal solution that leads to the lowest-cost functional parts.
Sigmetrix GD&T Consulting Services include:
- Ensure validity of GD&T
- Specifications may be permissible per ASME or ISO, but still not address part function
- Ensure your use/interpretation of GD&T is supported by ASME or ISO standards
- Functional GD&T Assessment
- Are the datum features identified able to perform the anticipated function?
- Do the tolerances indicate the same function you intend?
- Do the selected tolerances control all applicable variation?
- Determination of Datum Feature selection based on part functionality
- Can the selected datum features sufficiently constrain the part?
- Does the assembly reflect the selected datum features?
- Identify datum features and tolerances that may be adding unnecessary cost
- Additional datum features may clarify inspection/function requirements
- Profile may be used in place of other tolerances, but may be overkill and confusing
- Concentricity, while its name implies one thing, actually does something else.
- Symmetry, when a functional necessity, is not best controlled by “Symmetry”
- Conversion between ISO and ASME standards on your definitions
- Coaching the application of GD&T in inspection methods
- Clarify requirement changes when shifting from 2D drawings to MBD
How GD&T consulting works:
- Can be performed virtually, on-site, or a mix of both
- Can be part of a more comprehensive dimensional management effort
- Non-Disclosure Agreement is established
- Definitions are submitted for evaluation
- Marked-up versions returned per agreed scope
- Summary documents may be provided if consulting is not performed “live”
- Coaching is done “live” based on input from consulting participants
- Projects during product design before tooling phase
- Benchmarking current user understanding
- Teams new to GD&T
- Programs where GD&T is not a formal part of the design, manufacturing, and inspection processes
For best results, GD&T Consulting should be used in conjunction with tolerance analysis, either through our Tolerance Analysis Consulting or by your project personnel.