Dimensioning is necessary to define the shape and form of an engineering component. The basic principle of dimensioning has been covered already in Chapter 3 with respect to line types and thicknesses. This chapter continues the subject of dimensioning but considers some of the more fundamental principles of dimensioning and the implications with regard to inspection.
One of the problems of manufacture is that nothing can ever be made exactly to a size, even to atomic proportions. The surface of any component, even the smoothest, will vary. Thus, an inherent part of dimensioning must be a definition of the allowable variation. The permissible variation of a dimension is termed the tolerance. So, not only must dimensions be defined on a drawing but also tolerances.
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