7 Chapter 1 Introduction to Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. A tolerance specifi cation that correctly applies the symbology has a well-defi ned meaning. Where notes are used, the clarity of the meaning may be damaged by a poorly worded note, or the note’s meaning mis- understood by the person who reads it. Application of Computer-Aided Design in Product Documentation In 1967, a high school drafting teacher told a classroom full of students that, in the future, computers would be used to create the drawings that the students were at that time creating manu- ally. Those students had yet to see or use a computer. It was diffi cult for them to fathom the thought of a machine doing what they were doing through the use of manual drafting instruments and application of learned methods. Those who went on to become drafters or engineers saw in their lifetime a monu- mental change in product documentation methods. The use of computers in the design and drafting process began to fl ourish around 1980. As computers became faster and software became more capable, product defi nition started transitioning from man- ually produced two-dimensional (2D) multiview drawings to three-dimensional (3D) models with multiview drawings created from the models. Today, there remains a need in some companies to use multi- view drawings, but many have transitioned to using CAD models as their complete product defi nition. CAD systems are now widely used for creating mod- els, saved views, and multiview drawings. The dimensioning and tolerancing methods defi ned herein are just as important in creation of an annotated model containing the model and annota- tion as they are in creating 2D drawings made up of orthographic views. Dimensions may be displayed on the model, or they may be attributes of the geome- try that can be obtained by a query of model features. Tolerances applied to a model are usually visible in the model, and since the tolerances are associated with features, they become attributes of those features. As software continues to advance, users of the prod- uct defi nition will be able to use model attributes in the fabrication and inspection of produced parts and assemblies. Some companies already use model attri- butes in their analysis processes and in production. As previously mentioned, ASME Y14.41 provides application requirements specifi c to models and illus- trates applications explained in ASME Y14.5. ASME Y14.5 also contains some application examples for models. Whether or not the methods in ASME Y14.41 will eventually be covered in ASME Y14.5 is unknown. It is important to understand that ASME Y14.41 only shows specifi c examples of design applications for models. The absence of a specifi c fi gure or explanation does not prohibit application of the principles. Clearly communicating the dimension or tol- erance requirement is the essential thing to achieve. The methods shown in ASME Y14.41 are to be used on models, but where those methods do not adequately meet the need for clarity, the methods in ASME Y14.5 should be applied in a clear manner. Regard- less of the standard used to guide the application of dimensions and tolerances on a model, the product defi nition should invoke ASME Y14.5 as the basis for the meaning of dimensions and tolerances. Design through Teamwork Product cost can be minimized by involving people from various disciplines in the design process. Many designers are knowledgeable about manu- facturing and inspection processes however, they may not know all the specifi cs about the operations. Teaming with manufacturing engineers, machinists, tool designers, tool fabricators, and inspectors is important in making sure the design can be pro- duced at the lowest possible cost while achieving the intended design function and ease of assem- bly. The ability to produce a product at the lowest possible cost while attaining the desired quality is commonly referred to as producibility. Collaboration with the previously mentioned disciplines can help in many ways. Basic design concepts can often be improved through ideas from people who must operate the machines that produce the parts. These people know the capabilities of the machines. Designers usually have some knowledge of machine capabilities and processes, but it is diffi - cult to be as well informed as the machine operators. Technology changes too fast for one person to remain fully knowledgeable about everything in all fi elds affecting a design. People who work full-time in a discipline can provide accurate and valuable advice. Designers and design engineers must determine how to use the advice of others to create the optimum design that meets the functional requirements of the product. Part of the design process is to make deci- sions about how to show the dimensional require- ments and the tolerances. Once again, input from the previously mentioned disciplines can be very helpful. There are signifi cant advantages to having all disciplines review the product defi nition as it is completed. Comments can be acted upon before the product defi nition is fi nished. This reduces the need for changes after the design is released and produc- tion is started. Another important advantage is the fact that everyone involved in the design process will justifi ably feel the design belongs partly to them.