17 Chapter 1 Introduction to Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. The minimum requirements for any CAD sys- tem are a computer and CAD software. The capabili- ties and prices of CAD software vary. CAD software ranges in cost from free 2D packages to highly advanced and expensive 3D design systems. A CAD system usually includes more than just the computer and CAD software. It may include out- put devices to make hard copies (paper copies) of the CAD design fi les. Additionally, many companies use 3D printers to produce full size or scaled prototypes of CAD models. Some companies use 3D printing processes to make production parts. Variation analysis software may be integrated with the CAD software or operated as a stand- alone system. The variation analysis software can be used to simulate the 3D variation effects, within an assembly, that result from detail part tolerances, tooling tolerances, assembly sequences, and assem- bly constraints. Software for creating the computer fi les for running CNC machines is commonly known as computer-aided manufacturing (CAM) software. CAM fi les can be generated from CAD fi les. The designer may create a CAD design fi le that defi nes part requirements, and a manufacturing engineer or machine planner may use the CAD fi le and special- ized software to create a CNC machining program. Some companies are now greatly reducing or eliminating the need for hardcopies. The intent is to have the designer create an annotated model that provides complete product defi nition. The annotated model fi le is then used to create the CNC machin- ing program that runs the production machines. The CNC machining program can be created with- out the use of a paper drawing. An annotated model can also be used to create a computer fi le to operate an inspection machine. One type of inspection machine is called a coordinate measuring machine (CMM). One type of CMM is driven by a computer fi le called a CMM fi le. The CMM fi le is created from the annotated model and no paper drawing is needed. Creation of the annotated model, machining program, and inspection fi le can be completed with- out the generation of any paper. When the design fi les, manufacturing fi les, and inspection fi les are all created without any need for paper documents, this type of operation is commonly referred to as the paperless factory. The effect of being able to directly utilize an annotated model is that many companies now place their requirements directly in an annotated model and no drawing is created. Although some people still desire to see a hard copy in the form of a 2D drawing, the cost savings of directly applying requirements as annotations in the model appears to be a driving factor. Manufacturing teams are learning to work directly from the annotated models and the trend is toward the elimination of 2D drawings. Many companies that have the ability to create annotated models, drive CNC machines with CAM fi les, and complete inspection of parts with CMM fi les no longer need to have dimensioned multiview orthographic drawings. Any detail requirements that need to be shown can be documented in a saved view that is defi ned and stored in the annotated model fi le. The dimension values are defi ned by the model geometry attributes, and only the tolerances are applied graphically. Some CAD software can be used to apply the tolerances graphically on the model geometry or in a saved view and also associate the tolerances to the features such that other programs can access the information. Regardless of whether the CNC and CMM machines are programmed using dimensions directly generated from an annotated model or manually input from a drawing, there must be a method for “telling” the machines, or the people running them, how much variation is permitted. This means that tolerances must be applied on the model geometry or drawing views in some manner so that downstream users of the design data know the part requirements. The correct way to apply the tolerances is through the practices defi ned by the applicable ASME stan- dards and as explained in this book. CAD capabilities have already greatly reduced the number of paper drawings created. For many companies, these technologies have eliminated the need to show the dimensions on the model geome- try, but they have not eliminated the need to indicate tolerance requirements. The changes that the future holds will require a continual learning process for people to remain com- petent in their professions. Learning the information in this book will provide the knowledge necessary to work to the requirements defi ned by the cur- rent dimensioning and tolerancing standard and to prepare for the future.