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Geometric dimensioning and tolerancing

Geometric Tolerancing

By STG Machine

Geometric Dimensioning and Tolerancing, which is also known as GD&T can be considered as the standards and symbols that are being used by manufacturers and engineers to describe a specific product. In other words, they use this as a language to facilitate communications and end up with precise results at the time of production.

Geometric Tolerance Should Never be Ignored 

Tolerance refers to the variation that is allowed in technical drawings. When you isolate tolerance, you will notice that it is small and negligible. However, tolerance is still powerful, and it has the ability to give life to numerous negative consequences. 

At first glance machined parts may look straight and flat. If you measure these parts with an indicator or a caliper, you will be able to discover numerous imperfections all around it. If these imperfections fall within the limits of tolerance then the part is in compliance.

Consequences of Geometric Dimensioning and Tolerancing

Tolerancing refers to imperfections. These imperfections can lead you to numerous struggles with manufacturing a product. In other words, the presence of tolerance can make the process of manufacturing complex and difficult. Due to the same reason, it has the ability to affect the price as well as the lead time. Hence, it is important to have a complete understanding on how to minimize the effects of tolerances.

Base Material can Affect Tolerance in Different Ways 

Another important thing to keep in mind about tolerancing is the material. Aluminum is associated with a lower tensile strength. For the same reason, it is possible to alter aluminum quite easily. However, stainless steel and steel are associated with higher tensile strengths. Hence, it would cost more time, effort and money to achieve tight tolerances.

What is Geometric Dimensioning and Tolerancing? 

Geometric Dimensioning and Tolerancing can be considered a new standardized method for engineers. Traditional linear tolerancing was associated only with plus and minus calculations and it is quite ineffective. Utilizing tolerances with GD&T, eliminates many inefficiencies.

As such, an engineer will go ahead and design a part while ensuring perfect geometry. However, the manufactured part will never be perfect in the real world. This is where Geometric Dimensioning and Tolerancing comes into play. It helps identify and ensure that critical dimensions are held in order to ensure the design meets all necessary requirements.

Geometric Dimensioning and Tolerancing is essentially a design language. It offers a precise and clear way to communicate between suppliers, customers, and the production teams. This method can also be used to calculate worst-case mating limits. Furthermore, it offers a common language that can be used to express the intent of the design and critical features in an effective manner. Common GD&T callouts include:

  • Straightness
  • Flatness
  • Circularity
  • Cylindricity
  • Profile of a surface
  • Perpendicularity
  • Angularity
  • Parallelism
  • Position
  • Concentricity
  • Circular run-out
  • Total run-out

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