Page:Sheet Metal Drafting.djvu/179

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74. Short Handled Dipper.—The dipper presents a problem in which three right cones are mitered. The elevation, Fig. 236, is drawn and dimensioned. The handle of the dipper is raised about 10° above the horizontal, although there is no set rule governing this feature. The boss is also drawn to suit the ideas of the designer.

Pattern of Boss.—Figure 237 is a reproduction of the elevation of the boss and that part of the dipper that is adjacent to it. The sides of the boss are extended to form a right cone. This right cone is cut by two planes, the surface of the body being one cutting plane, and the line of junction between the boss and the handle, the other. A half-profile is drawn directly upon the base of the cone, and divided into equal parts. These parts are numbered and extension lines drawn from each division, perpendicular to the base of the cone. From each intersection of the base, lines are drawn to the apex.

A half plan of the boss is drawn directly above the elevation. A quarter-profile is attached to the half plan, with divisions and numbers that correspond to the profile in the elevation.

From each point of intersection on the slant height of the body dotted extension lines are carried up to the horizontal center line of the plan. Using the center of the top as a center point, arcs are drawn from each intersection of the dotted lines and the horizontal center line. These arcs intersect extension lines drawn from the base to the apex in the half plan. Perpendicular lines are now carried back to correspondingly numbered extension lines in the elevation. A curved line passing through the points thus obtained will be the developed miter line.

An arc of stretchout is drawn using a radius equal to the distance from the apex to point 4. Upon this arc are placed twice as many spaces as there are in the half-profile, with numbers to correspond. Measuring lines are drawn from each of these divisions, to the apex.

From each intersection of both miter lines, extension lines are drawn parallel to the base of the cone until they intersect the slant height. From each of these points, extension arcs are drawn