54 Welding Print Reading Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. To obtain the views, think of the object as being enclosed in a hinged glass box. Study Figure 5-5 carefully. Imagine that the views are projected on the sides of the box. The top view of the object is seen on the top of the box, the front view on the front of the box, and so on for the remaining views. This tech- nique is called orthographic projection. It permits a three-dimensional object to be described on a flat sheet of paper having only two dimensions. As can be seen, at least six views will be devel- oped. Not all of them, however, are needed. Only those views required to give an accurate shape description of the object are included on the print. A view that repeats the same shape description as another view is not used, Figure 5-6. The principal views commonly shown on a print are the front view, top view, and right side view. In the United States and Canada, all engineering drawings are drawn in third angle projection, with the object drawn as viewed in the glass box and the views projected to the six sides of the box. The pro- jected views are drawn to resemble views when the box is opened out. The top view is always directly above the front view. The right side view is to the right of the front view and in line with it. The left side view is to the left of the front view. Drawings used in European countries are some- times drawn in first angle projection, with the object drawn as if it were placed on each side of the glass box. Figure 5-7 shows both third angle and first angle projection. Compare the two. The main differences include how the object is projected and the arrange- ment of the individual views on the drawing. The type of projection angle is usually identified on the drawing by ISO (International Organization for Standardization) symbols, Figure 5-8. Auxiliary Views The true shape and size of objects having angu- lar or slanted surfaces cannot be shown using the principal (top, front, side) views, Figure 5-9. The true length of the angular surface in Figure 5-9 is shown on the front view, but this view does not show its width. The true width of the angular surface is shown on the top and side views but neither view shows its true length. Figure 5-5. Note relationships among views by thinking of the object as enclosed in a hinged glass box.