Chapter 1 Geometric Dimensioning and Tolerancing Essentials 25 Copyright Goodheart-Willcox Co., Inc. Computer-Aided Design and Drafting (CADD) Computer-aided design and drafting (CADD) is the process of using a computer with CADD software to design and produce drawings and models. Today, most designers use CADD software to produce drawings and models according to specific indus- try and company standards. The terms computer‑aided design (CAD) and com- puter‑aided drafting (CAD) refer to specific aspects of the CADD process. The most common CADD formats used in the manufacturing industry are 2D multiview draw- ings and 3D solid models. See Example 1-22. 3D surface models are also common, but they are often used for specific applications such as forming complex boundaries. A solid model is the most complex type of 3D model, and it contains information about object edges, vertices, surfaces, and mass. Solid models enclose a volume. A surface model is a 3D model that contains information about the object edges, vertices, and outer boundaries of the object, known as surfaces. Surface models have zero thickness, lack mass, and may not enclose a volume. Orthographic View Meaning 0.25 Diameter cylindrical tolerance zone at MMC 15 40 Basic dimension symbol Position geometric characteristic symbol 0.25 Diameter geometric tolerance Maximum material condition (MMC) symbol Feature control frame Two 14±0.2 diameter holes 13.8 Diameter at MMC Goodheart-Willcox Publisher Example 1-21. Geometric tolerancing uses basic dimensions and positional tolerancing with a cylindrical tolerance zone to overcome tolerance buildup.