Geometric Dimensioning and Tolerancing (GD&T) is a symbolic language, crucial for defining the geometric characteristics, and tolerances on a part and assemblies. It provides standardised symbolic language to the designers, manufacturers and inspectors to convey the necessary information in the designing and manufacturing process to eliminate mistakes that could appear during the process.

2D technical drawing on background. White GD&T title with a control frame in the center. Kreon logo

What is GD&T?

GD&T ensure clear-cut communication using technical terminology of geometric characteristics, such as flatness, concentricity, cylindricity, profile of a shape, true position and runout despite country location and different methods of communication.

This language is encoded in symbols and annotations indicating some specific rules- describing its tolerances, references, and the relationship between features to ensure the manufactured part meets the desired specifications. It helps to make sure that the different parts of a product should be shaped and positioned relative to each other, and that they fit together correctly to perform their intended functions. This improves the consistency and quality of manufactured products.

2D technical drawing with gd&t basics annotations

Understanding each term in GD&T

The (GD) Geometric Dimensioning in GD&T refers to the process of stating explicitly and controlling the geometric dimensioning of features of a part. It illustrates clearly the geometric elements (plane, circle, line, etc…) on a specific zone relative to a particular part.

Tolerancing (T) in GD&T involves specifying the allowable variation that can be done in dimensions and other characteristics of a part. It makes sure that the part will function correctly corresponding with the relative parts and within its tolerance zone specified by GD&T.

Part with gd&t symbols of flatness, of position, of cylindricty, of perpendicularity and coaxiality

How does GD&T function: step by step explanation

To manufacture a part with its required features, GD&T express the geometric characteristics, dimensions and specified tolerances by using symbols and notations to form the blueprint for subsequent manufacturing steps. In the past, information was typically conveyed using 2D technical drawings. Nowadays, modern GD&T software integrates this information directly into the 3D CAD model (Computer-Aided Design), eliminating the need for traditional 2D technical drawings in design.

For each feature, it then creates a control frame containing all information such as symbol, tolerance, material, and datums like planes, cylinders and circles to ensure consistent measurement references.

After manufacturing the parts, and to ensure compliance of the entities with GD&T specifications, precise control must be carried out. The process then employs measuring arms, Coordinates Measuring Machines (CMMs), 3D Scanners and other metrology tools for quality control and inspection.

The measured data (obtained by scanning or probing) and GD&T tolerance are further applied to compare to the nominal (theoretical) CAD model to identify any variations in the manufactured part and validate if the inspected features of the part are within the acceptable limits. All inspected data including the 3D scans and reports are documented for traceability and future reference to understand the manufacturing process, identify trends and improve the overall quality.

Description of GD&T control frame: leader arrow, symbol, tolerance zone, tolerance value and datum reference

GD&T symbols and characteristics

GD&T example: flatness

Let’s say you have a metal plate with a specified flatness tolerance of 1.00 mm. If the flatness is called out on a drawing using GD&T, it might be represented as follows:

Flatness: 1.00 mm

This means that the entire surface of the metal plate must not deviate from a true flat plane by more than 1.00 mm. Inspectors would use measurement tools such as surface plates, straightedges, or specialized equipment to check and verify that the actual surface conforms to the specified flatness tolerance. If the measured deviations exceed the tolerance, it would be considered non-conforming.

Example of flatness tolerancing

Why GD&T is important?

Technological and manufacturing advancements in engineering patterns and designs are evolving into complex and sophisticated structures. To understand these structures, the machinist requires the most precise and trustable method of communication. It is where GD&T’s role comes into play, it allows manufacturing experts to communicate clearly in a universal language that everyone agrees resulting in saving more time, lessening costs and making the production process efficient.

Manufacturing a complex part demands a great effort from the very initial stages of designing. The more composite the design of the product gets, the more compact the tolerances are. If the specification of the parts is conveyed appropriately in the process it can avoid the scrappages. Hence, it requires high-level metrological tools such as 3D scanners, measuring arms, and CMMs for quality control and inspection. These tools help to meet the quality control requirements of any project and in any circumstances.

zoom on an engine

GD&T Standards

Engaging in Geometric Dimensioning and Tolerancing (GD&T) inspections presents certain challenges, with some issues being the potential for misinterpretation. Despite the clarity in annotations and definitions, there exists a need for comprehensive training for both designers and inspectors to accurately apply and understand GD&T principles.

There are presently two primary sets of standards governing Geometric Dimensioning and Tolerancing (GD&T). The Geometrical Product Specifications, referred to as ISO GPS Standards, is a collection of standards published by the International Organization for Standardization (ISO). Concurrently, the American Society of Mechanical Engineers (ASME) issues the ASME Y14.5 Standard, shaping the landscape of GD&T standards in the United States.

ASME and ISO logos

Discover how Kreon’s 3D measurement tools are perfectly adapted solutions for the GD&T verification

Unmatched accuracy and portability

Kreon’s measuring arms offer unparalleled flexibility, allowing inspections to be carried out in diverse settings, whether in workshop environments, measuring laboratories, or even outdoor facilities. These versatile arms maintain exceptional measurement quality while ensuring portability and ease of use. Particularly, the Onyx arm stands out for its precision, enabling seamless inspection of parts through probing to verify tolerances stipulated by GD&T, thereby ensuring that components meet exacting specifications.

Onyx Skyline scanning arm

Integrated scanning solutions for enhanced productivity

Skyline 3D Scanners are perfectly integrated with measuring arms to provide scanning solutions to any complex part in the blink of an eye regardless of their size, shape, or material.

Kreon’s high-performance Skyline range of 3D scanners are tailored for all kinds of applications in any industry such as automobile and aerospace. Depending on the model, Skyline’s proficiency in scanning intricate parts with its large laser width of 200 mm, lightning-fast speed at 600,000 pts/sec and accuracy of 9 μm is crucial for precise measurements. It enhances quality control, where manufacturing variations can have significant implications on product performance and compliance.

Skyline range: Skyline EYES, Skyline WIDE and Skyline OPEN 3D scanners

CMM scanning for accuracy and automation

Kreon’s most accurate scanning range of 3D Scanner Zephyr III delivers an unrivalled accuracy of 5µm with an advanced scanning speed of 600,000 pts/sec. Zephyr III is the epitome of accuracy in 3D Scanners to meet rapidly growing productivity needs in the industry.

Embedding more than 30 years of expertise in 3D Scanning, Zephyr III 3D Scanner sets a standard of the high level of scanning technology making it possible to perform numerous operations such as GD&T analyses and color mapping, with complete confidence.

Zephyr III 3D Scanners are fully automatised and integrated on CMM to scan automatically in multi-oriented positions, constantly improving the control time while controlling the full part. Zephyr III has a lot to offer when it comes to capturing meticulous details – high acquisition frequency (300hz) and 300 mm wide line (Zephyr III 300). With CMM, Zephyr III streamlines the inspection process, improves efficiency, and ensures accurate GD&T assessments.

Zephyr III scanners are not limited to a specific platform; they can be used with robots, portable CMMs, and CNC machines to provide more precise scanning.

Zephyr III 3D scanner and CMM

Patented probe under the Kreon 3D scanners

The integration of probes under the scanners on the measuring arm is a patented solution by Kreon. This innovation enables seamless scanning and probing within the same measurement range, eliminating the need for disassembly and saving valuable time. This unique combination enhances versatility, allowing for precise probing of geometric entities, such as verifying GD&T specifications, and swift scanning of entire parts to detect surface deformations or defects.

From automotive to aerospace, these advanced metrology tools empower manufacturers to deliver superior products that meet customer expectations and regulatory requirements.

Probe connection under a Kreon 3D scanner

Meet our metrology software solution for 3D scanning: Zenith

Kreon’s commitment to performance and innovation provides Zenith, with a software designed for Kreon measuring arms and easily manageable for scanning and probing any industrial parts for quality control. Zenith’s extended capabilities not only provide fast cloud acquisition but also deliver a CAD comparison through extraction from CAD and color mapping.

GD&T system is incorporated within the Zenith software making it well-suited for demanded parts. Zenith is configured to handle key GD&T aspects such as form tolerances (flatness, cylindricity, circularity), orientation tolerances (perpendicularity, parallelism, angularity), and position tolerances (coaxility, concentricity). Moreover, Zenith’s advanced sectioning functions allow users to create sections of both nominal and measured parts, enabling distance analysis and angles, for in-depth GD&T tests.

Position tolerance example with Zenith software

In conclusion, Kreon’s measuring arms, 3D scanners, and software solutions emerge as indispensable assets in the realm of GD&T verification and quality control. By seamlessly integrating advanced technology with precision engineering, Kreon empowers manufacturers to uphold rigorous GD&T standards, enhance productivity, and deliver products of exceptional quality across various industry sectors.

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