Why do We Need GD & T?

GD&T,short for Geometric Dimensioning and Tolerancing, is a system for defining and communicating the design intent that helps designers to communicate to the manufacturer how much geometrical imperfection is tolerable without compromising the intent of the component.

What do GD and T mean?

Geometric tolerances and tolerancing is a language of symbols used to describe a part of nominal geometry and the allowable tolerance. When applied properly, the design engineer can define the size, shape, feature, location and orientation of the part. GD&T is introduced as an addition to the coordinate dimensioning system, not as a replacement. The GD&T methodology takes into consideration the function of the part and how it functions at the assembly level. Therefore, for the proper application of GD&T, the designer engineer should have a clear understanding of the function of the part.

GD&T concept was founded by a Scotland engineer Stanley Parker from the Royal Torpedo factory working on naval weapons during world war II. He came up with true position or position tolerance in 1938.GD&T standard is defined by the American Society of Mechanical Engineers(ASME Y 14.5 - 2018 ) for the USA and ISO 1101-2017 for the rest of the world.

The Drawback of using traditional dimensioning and tolerancing is that they denote individual part and part feature information. It does not guarantee how well the part fits and functions at the assembly level, as most parts are not useful by themselves. It is important that parts must fit well with each other. This is why we must be 100% certain to ensure that the part will fit and function at the assembly level. The 

The precise relationship between the geometrical feature of parts is achieved by the application of the following geometric characteristics : 

• Flatness
• Straightness
• Circularity 
• Cylindricity
• Angularity
• Perpendicularity
• Parallelism
• Position
• Symmetry
• Concentricity
• Profile of surface
• Profile of Line 
• Circular runout and total runout

What are the Benefits of GD&T?

The key benefits of GD&T are as follows :

• Enhanced communication - The single and standardized GD&T language ensures cross-functional teams communicate clearly and accurately with each other. This helps reduce confusion and misunderstanding, leading to delay and rework.  
• Improves reliability and Quality- By using GD&T, manufacturers can ensure that parts are manufactured to precise specifications and that they meet the requirement of the end user. This helps ensure that products are of high quality and will function properly. 
• Increased Flexibility -  General rule of thumb, designers should keep the tolerance as large as possible while maintaining the design intent. Small or tight tolerances can increase the cost of manufacturing, inspection and tooling for manufacturing parts.
• Saving Money- By applying GD&T, designers can provide appropriate tolerance that maximizes production and helps manufacturers make the most efficient use of materials and resources. This reduces waste and increases productivity, leading to lower costs and improved efficiency. 

In conclusion, GD&T is an essential tool for ensuring that the parts and assemblies are manufactured and assembled to the correct specifications and tolerances. It allows for Clear communication Between engineers, designers and manufacturers, allows for greater flexibility in the manufacturing process, improves the overall quality of the final product and helps to reduce costs and improve efficiency in the manufacturing process. Without GD&T, the manufacturing and assembly process would be much more difficult and prone to errors, leading to increased costs and decreased efficiency.