1 Copyright Goodheart-Willcox Co., Inc. CHAPTER 1 Introduction to Dimensioning and Tolerancing Technical Terms annotated model annotation attributes computer-aided design (CAD) dimension dimension value fi rst angle projection geometric dimensioning and tolerancing (GD&T) model model geometry model value nominal size orthographic projection positional tolerancing producibility product defi nition data product defi nition data set projection lines query resolved value Royal Cubit saved view SI system supplemental geometry third angle projection tolerance US Customary system Objectives Information in this chapter will enable you to: → Explain the importance of specifying dimensions and tolerances in compliance with applicable standards. → Recall the history and development of dimensioning and tolerancing methods. → Explain how teamwork can result in better defi nition of the dimensions and tolerances in the design process. → Recall the job titles of those who can assist on the design process team. → Recall the dimensioning and tolerancing skills needed for success in design- or production- related occupations. → Identify and explain the types of documentation included in a product defi nition data set. → Understand the relationship between 2D orthographic views and how they are created using orthographic projection. → Explain some possible industrial changes and the impacts of these changes on dimensioning and tolerancing. This highly competitive, industrial world requires full advantage be taken of all methods that help improve effi ciency and reduce product cost. Current dimension- ing and tolerancing standards defi ne methods for increasing clarity of requirements and specifying the needed accuracy. A good knowledge of dimensioning and toler- ancing methods is needed to ensure clear specifi cation of part requirements. Clarity in specifi cation ensures the design intent is communicated to manufacturing. Allowable manufacturing variation may be maximized through careful tolerance calculations and proper application of the calculated tolerance values using standardized methods. Proper application of dimensions and tolerances enables maximizing tolerance zones without reducing product quality. Where clarity in tolerance specifi cation is achieved, that clarity benefi ts the manufacturers of parts because they can determine from the product defi nition exactly what is required. This enables the manufacturer to match the appropriate and least costly processes to the specifi ed requirements. Introduction