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286 22.1 Two-Dimensional Irregular Shapes Most of the scenic units discussed in the previous chapters on shop drawings have had rectilinear shapes. For the most part, however, scenery does not fit into this convenient world of right angles. For purposes of discussion, we refer to these nonrectilinear forms as “irregular shapes,” due to their free-form or nonperpendicular profile lines. (A profile, of course, is an outline shape, drawn either with a straight edge or freehand, two examples being the skyline view of a group of buildings, and the leaves on a tree.) The development of useful shop drawings for irregularly shaped units requires a knowledge of, and confidence in, actual construction practices. It is important to recognize that in a scenic studio it is difficult to accurately project angles other than right angles. The carpenter can make use of a tape measure, framing square, and the “3-4-5 triangle” axiom for 90° angles, but there is no such ready combination of tools to develop other angles. (Based on the Pythagorean theorem, the “3-4-5 triangle” axiom states that any triangle with sides in proportions 3, 4, and 5, or their multiples [9, 16, 25, etc.] is a right angle.) Given the long distances that need to be projected in the construction of scenery, it is necessary to examine other methods of dimensioning oblique and acute angles, noting that the increased availability of laser shop tools has signifi­ cantly enhanced the accuracy of results. 22.2 Dimensioning TwoDimensional Irregular Shapes One way to provide the information necessary for the construction of irregular units is to surround the object with a grid of right-angle dimensions, that is, with a system of coordinate points (fig. 22.1). These points are developed by placing the unit within a rectangular envelope, equal in size to the object’s extreme outside dimensions. One corner of the rectangle is selected as the 0,0 point of intersection on an X,Y grid. Once this is done, all significant points are located within an imaginary envelope drawn with measurements that emanate from the base lines. This technique is useful when dimensioning an object with oblique straight lines. 22. Profile Units, Soft Goods, and Similar Design Elements A second method of describing the layout of a unit with oblique angles is through the use of triangulation. In this procedure, an irregular flat is subdivided into triangles, using temporary diagonals (fig. 22.2). The object can then be reconstructed readily by using a compass and the process of triangulation. This operation is easily repeated in the scenic studio using a set of trammel points. Once a base line and its perpendicular have been established on the studio floor, the outline of the flat is determined using triangulation (see section 5. 8). 22.2 Triangular dimensioning of an irregular shape 22.1 Perpendicular dimensions of an irregular shape 287 Triangulation is usually faster than developing a rectangular grid, but when working with extreme distances it is not as accurate. Unless working in a CAD application, you should not use the actual angle measurements with either of the above methods unless the precise length of the sides and degrees of the angles have been checked mathematically. No hand drafter, regardless of experience or skill, can work in small scale with enough precision to determine this information solely by graphic means. On the other hand, CAD solves this dilemma, since the program lists the properties of each line, citing its precise length and angle (up to 8 decimal spaces) with respect to the established coordinate system. 22.3 Profile Flats Many carpenters find profile flats among the most fascinating scenic units to build. With good painting techniques, a flat piece of wood and canvas can be made to seem perfectly threedimensional when viewed directly from the front. The fabrication of profile flats, however, requires a different approach to framing and handling than that applied to conventional flats. A rear elevation shop drawing of the desired framing should be developed by the drafter to reduce the decisions required of the carpenter and to make the most efficient use of time and materials (fig. 22.3). Using a mirror image of the designer’s front elevation , framing is applied to adequately support the irregular shape and to divide the unit into smaller pieces if necessary for easier handling or storage. When using CAD to redraw a hand-drafted profile, one straightforward approach is to scan the scaled image and...

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