Chapter 1 Geometric Dimensioning and Tolerancing Essentials 3 Copyright Goodheart-Willcox Co., Inc. machinery, buildings, electronics, infrastructure, and maps. GD&T relates to design applications and processes used in mechanical drafting and manufacturing. Mechani- cal drafting is the form of drafting used by the manufacturing industry. Engineering drafting is another name for mechanical drafting. GD&T offers a comprehensive method to convey dimensions, tolerances, and part requirements that would otherwise require extensive notes and more interaction between designers and manufacturers. Example 1-2 shows the control arm stop from Example 1-1 defined using dimensions, tolerances, and notes. Compare Examples 1-1 and 1-2 to understand how GD&T improves drawing efficiency. Notice that symbols are used instead of notes to specify requirements. Symbols are less prone to misinter- pretation than notes. In addition, symbols are faster and easier to apply to a drawing, and they occupy less space on the drawing area. GD&T defines design requirements in a way that clarifies the amount of accuracy and precision necessary for the desired form, fit, and function of a product. History of Engineering Drawings Some of the earliest engineering drawings depict machines. In the 14th and 15th centu- ries, drawings of machines and mechanical devices were created by hand as pictorial sketches. The drawings included handwritten explanations that provided guidance on how a machine or device was fabricated. Craftworkers used the drawings as a gen- eral reference and applied their technical knowledge and experience to fabricate the product. Dimensions did not appear on the drawings and were unnecessary because each end product was unique. Over time, technological developments brought about greater awareness of the need for creating accurate engineering drawings. The Cartesian coordinate system is named after the French mathematician Rene Descartes, who wrote about the system in the 1600s. Also known as the rectangular coordinate system, the Cartesian coordinate system locates points in space according to distances from the X, Y, and Z axes. Carte- sian coordinates are used to locate points accurately and precisely and have numerous applications in engineering and manufacturing processes. The development of descriptive geometry techniques led to new methods for rep- resenting objects on drawings. In the late 1700s, the French educator Gaspard Monge devised a way to use descriptive geometry techniques to “project” views of objects. Descriptive geometry is the method of technical drawing concerned with using planes of projection to obtain 2D views from 3D geometry. The principles of descriptive geom- etry are the basis behind the techniques used in orthographic projection. Orthographic projection is a method of projection in which features of an object are projected onto an imaginary projection plane located parallel to the object. The accuracy of drawings improved as they evolved from artistic sketches and line drawings to orthographic view drawings. A drawing made up of orthographic views is called a multiview drawing. A multiview drawing is a representation in which two or more 2D views are used to define the size and shape of an object. The drawings shown in Examples 1-1 and 1-2 are multiview drawings. Each drawing has a front view, right-side view, and pictorial view. The views on a multiview drawing are placed in a standard arrangement and are directly aligned with each other. As methods of creating engineering drawings advanced, drawings started to take on greater importance and designers came to realize the need for accurately dimen- sioned drawings. This awareness became more pronounced in the 1800s during the Industrial Revolution when mass production methods emerged and established the need for greater accuracy in design and manufacturing.