78 Print Reading for Industry Copyright Goodheart-Willcox Co., Inc. to understand the principles of orthographic pro- jection. Through this unit, other principles will be examined. Understanding these principles will help an individual develop the visualization and interpretation skills necessary to read and interpret prints. Selection of Views Since there are three dimensions in space, an object can be viewed from the right or left, top or bottom, and front or back, resulting in six principal views. In the past, the term normal has been applied to describe these views. In this text, the term prin- cipal is used to mean “main” or “primary,” as defined by the Y14.3 standard. However, only those views necessary to clearly describe the object need to appear in the drawing. Seldom is an object so complex that all six principal views are required. Usually, the necessary details can be shown in two or three views. Three views will almost always fully describe an object, but more views can be used if there is a lot of detail on the opposite sides of an object. Directions other than the six principal directions are defined as auxiliary views, which are discussed in Unit 7. In educational settings, the front, top, and right side views are typically used to describe an object, and may be referred to as the three regular views. This type of drawing can also be referred to as a three-view drawing. Of course, in industrial applications, there is nothing that mandates the three regular views. As well, many objects made of flat sheet metal may only require one view, while cylindrical objects may only require two views. The following rules will help in the selection of views. • Only views clearly describing the shape of the object should be drawn. • Views containing the fewest hidden lines should be selected. Compare the two side views in Figure 5-7. • If practical, the object should be drawn in its functioning (operating) position. • If practical, the view best describing the shape of the object should be selected as the front view. Dimensions of an Object One of the keys to reading a multiview drawing is familiarity with the terminology used for the dimensions of an object. Each projected view is two dimensional, even though the object is three dimen- sional. It is critical to discuss the dimensions of an object using standard terms. Throughout the field of drafting, the three terms predominantly used for the three dimensions of an object are height, width, and depth. Height is defined as the top-to-bottom mea- surement for an object, from the vantage point of the front view, which may or may not be the “front” of the object. Width is defined as the left-to-right measurement of an object, also from the vantage point of the front view. Depth is defined as the front-to-back distance of the object, as based on the orientation of the object for the views. Even though the object described by a print is three dimensional, each projected view is only two dimensional. The height and width of the object are shown in the front view, but not the depth. The width and depth of the object are shown in the top view, but not the height. The height and depth of an object are shown in the right side view, but not the width. See Figure 5-8. Standard- izing the terms used for the dimensions is critical to studying print reading and completing the exercises in this unit. Visualization of Objects Another useful tool in studying projection theory is identifying particular “rules” of behavior for surfaces and edges as they project onto pro- jection planes. This section examines how flat, or Goodheart-Willcox Publisher Figure 5-8. The three standard terms for the dimensions of an object are height, width, and depth. Top Front Right Side