Unit 5 Multiview Drawings 83 Copyright Goodheart-Willcox Co., Inc. A multiview line can also simply represent an intersection—an edge where two surfaces meet and nothing more. In drawings of objects with curved lines, a third meaning a multiview line can have is the maximum contour element of a curved surface. In some views, this will be represented by a line. As with the other principles of projection discussed pre- viously, understanding these principles will enhance both your visualization and interpretation skills. First-Angle and Third-Angle Projection The system of projection explained earlier in the unit is common throughout the United States. The projection of a view is basically what the viewer sees when looking at the object through the glass projection plane. The glass box is unfolded in such a way as to place the top view above the front view. This is known as third-angle projection. In many countries, especially in Europe, a slightly dif- ferent projection system is used that results in the views being located differently. The two projection systems used in industrial drawings are identified as third-angle projection and first-angle projection. These two types result from a theoretical division of space into four quad- rants by vertical and horizontal planes, Figure 5-18. The viewer of the four quadrants is considered to be in front of the frontal plane and above the hori- zontal plane. The views are arranged by folding the two planes into one by collapsing the second and fourth quadrants and the views are then seen from the front. As a result of this, there are no second or fourth angle projections. If there were, the views would overlap. Goodheart-Willcox Publisher Figure 5-17. This figure shows how to interpret several lines on a multiview drawing. A = Edge view of a flat or curved surface B = Intersection of two surfaces only (just an edge) C = Maximum contour of a curved surface B C C A A B A A C A C A C A B Goodheart-Willcox Publisher Figure 5-18. The two types of projection are based on a theoretical division of space into four quadrants. Quadrants two and four are not used. V i ewe r Viewer Hori zonta l Frontal 1 2 4 3