30 Geometric Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. Digital Product Definition Data A product definition data set is a set of model documentation used to define the phys- ical and functional requirements of a product. Also referred to as a data set, a product definition data set is a complete set of computer files documenting the model. The ASME Y14.41 Digital Product Definition Data Practices standard establishes required documentation practices for digital product definition. The standard provides guide- lines for applying annotations to 3D models created in CADD modeling programs. The content in a data set can include a model and its annotations, material data, notes, and any related documentation. The ASME Y14.41 standard establishes two methods of data set preparation: model only and model and drawing. In a model only data set, annotations defining dimensions and GD&T information are applied directly to the model. An associated drawing is not required. In a model and drawing data set, a model and drawing are used to define product requirements. A limited dimension drawing (LDD), also known as a critical feature drawing (CFD) or reduced dimension drawing (RDD), is an engineering drawing that relies on an associated model to define features. The drawing includes notes that direct the reader to the model for additional requirements and definition data. See Example 1-25. When a drawing is included in a data set, drawing views and title block ele- ments are to be created in compliance with applicable ASME standards. ASME Y14.41 specifies additional required practices for digital drawings, including requirements defining the relationship between a model and an associated drawing. For example, dimensions shown on the drawing must match the model geometry. Any models defined by the information on the drawing must be referenced on the drawing. When the model or drawing does not provide a complete definition of the product, this must be specified with a note. Computer-Aided Manufacturing (CAM) Computer-aided manufacturing (CAM) refers to the use of computer-controlled machine tools to automate manufacturing processes. Programmable machines such as milling machines, lathes, and laser cutting machines are used in CAM. This method of manufacturing is widely used in industry. Parts designed for production in a CAM system are normally created in CADD. To prepare the part for manufacturing, the CADD file is imported into CAM software to create a program for machining. In CAM, a program is a set of instructions in code form that define the actions and movement of machine tools to produce the part. In some applications, CADD and CAM tools are integrated into the same software. The combination of CADD technology with CAM processes is referred to as computer-aided design and drafting/computer-aided manu- facturing (CADD/CAM). Machine tools used in CAM are operated using computer numerical control (CNC). Computer numerical control (CNC) is the computerized control of machine tools by means of encoded instructions. The instructions defined in a CNC program establish the tool movement and speed, feed rate, tool changes, and coolant flow. The CNC program is used by a CNC machine to perform the necessary operations to pro- duce the part. This process allows for reliable and efficient production of parts.