TABLE OF CONTENTS 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.
When a part is to be dimensioned, the value and importance of any dimension will depend upon a variety of factors. These factors will be concerned with such things as the precision needed, the accepted variability, the function and the relationship to other features. In order to dimension correctly, a series of questions will need to be asked about a particular dimension and these will be dependent upon a clear understanding of the terminology associated with dimensions and tolerances. The following dimension definitions are important.
Although every aspect of a component has to be dimensioned, some dimensions are naturally more important than others. Some dimensions will be critical to the correct functioning of the component...
