Page:Sheet Metal Drafting.djvu/55

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23. The Garbage Can.—In developing the patterns for large objects such as a garbage can, Fig. 59, it is necessary to make the drawings to scale. Drawing to scale means making each line on the drawing one-half, one-third, one-quarter, or other fractional part of its true length. Scale rules are provided to assist the draftsman in this work. In order to understand the principles of the scale rule, the student should construct a model of one according to the following directions:

Suppose we wish to make a drawing to a scale of three inches to the foot (3&Prime;=1&prime;0&Prime;). This would call for the use of a rule having a three-inch scale. We will proceed to construct such a scale. Procure a strip of thin cardboard twelve inches long and one inch wide. Lay off along one edge spaces three inches apart. Each of these spaces will represent twelve inches on the finished article. How many feet of the finished product are represented by the entire rule? Mark these divisions 0, 1, 2, and 3. Divide the first space into twelve equal parts. Each new space represents one inch. Mark the third, sixth, and ninth spaces as shown. Each space representing one inch can now be divided into four, eight, or sixteen equal parts, in order to represent ¼ in., ⅛ in., or $$\scriptscriptstyle{\frac{1}{16}}$$ in. respectively. The rule shown in Fig. 60 is measuring a distance of three feet, four inches (3&prime;-4&Prime;). Notice that the feet are read to the right of the zero mark and the inches to the left of the zero mark.

The elevation of the garbage can. Fig. 61, should be drawn according to the dimensions shown. This elevation shows two O-G beads on the body of the pail. The size of these beads is not given, because the equipment of beading rolls varies with different shops. The necessary rigidity will be obtained regardless of the size of bead used. Bail ears are used on this job. The student's attention is called to the location of these ears. This can is designed for a cover that has a rim fitting inside of the body. If the cover rim were fitted over the outside, the ears would have to be placed below the bead and the bail lengthened to correspond. The development of the patterns is similar to the preceding problem and needs no additional description. All dimensions on the elevation and the patterns should be full size. These are