Geometric modeling provides graphic representations of real or abstract objects. Realistic representation requires three dimensional (3D) attributes since natural objects have three principal dimensions. CAD software gives the user the ability to construct realistic 3D models of objects, but often prints of these models must be generated on two dimensional (2D) standard-sized sheets. The transformation of 3D objects into 2D representations on standard-sized sheets requires one to use a proportional relationship called a scale, which is defined by a scale factor (SF). Two mathematical models for a scale factor, one for reduction scaling and the other for enlargement scaling, are presented for standard orthographic views. The models are based on the sizes of standard drawing sheets and the principal dimensions of the object. The application of the models is demonstrated with two illustrative examples, one for reduction scaling and another for enlargement scaling. The scale factors selected on the basis of the models were used to prepare detail drawings for the examples. In each case, the scale factor appeared satisfactory. It is shown that the models are tolerant of error in the only parameter that is assumed when applying them, suggesting that they are robust. This robust feature is an advantage, because in real design drafting situations, one must often make assumptions about sizes. The models can thus accommodate some erroneous assumptions. (Contains 4 figures and 5 tables.)