Page:Popular Science Monthly Volume 92.djvu/953

 Popular Science Monthly

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��methods. Fourth, divide the circle into sixteen equal parts. Project lines from these points direct to the base line, then direct to the apex; these are the radial lines. Fifth, from where these radial lines cross the joint line of the cone and cylinder, project lines straight across to

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Developing a pattern for an egg tester which is a truncated cone and round pipe

the line apex-1 to get the true lengths. Do the same with the V-shaped opening at the bottom. Sixth, draw the top and bottom pattern arcs, N-M and 1-9, getting the correct length by transferring the spaces from the bottom view circle. Seventh, from the numbered spaces on the pattern arc, draw lines to the apex. Eighth, take the true length points on line apex-1 and swing them over the pattern until they cross the same numbered line coming up from the pattern arc, making crosses. Connect these crosses with a free- hand curve. Ninth, to get the pattern for the V-shaped opening, get the true height by projecting straight across to the line apex-1, then swing the line over to radial pattern line, 5. To get the true width we must make use of "auxiliary points," as we have done once or twice before. On the front view project lines straight to the bottom view circle (points marked X). With your dividers take the distance on the circle from point 4-X and lay ofif on the pattern arc as shown in the drawing. Do the same for the other distance, 6-X, connect the three points and the one-half pattern will be complete.

��The illustration (Fig. 4) shows the de- velopmentof patternsfor a "Dust collector Intake." The technical description of this problem is "Rectangular four-sided Prism Intersecting a Truncated Cone off Center."

The steps in the development of the pattern are as follows: First, draw front view. A; the joint line cannot be drawn until the points are projected across from the side view, B. In this problem the joint line is absolutely necessary and is obtained by drawing the bottom circle on both front A and side B views (as only one-quarter pattern is needed, only one-quarter circle is drawn). Second, space and number each bottom view quarter circle as in the preceding problems. Be very careful to number these correctly. Notice that 1 is at the right on front view A, but in the side view B it is in the exact center. Third, from these numbered points draw lines straight up to the base line, then straight to the apex. Fourth, on side view B where the lines to the apex cross the end view of the rectangular pipe make marks as in the drawing and draw lines across to the front view, A. Where they intersect the same numbered lines coming up from the bottom make a cross. It will be noticed that if we use only the regular numbered lines coming up from the bot-

���A dust intake collector or rectangular four- sided prism intersecting a truncated cone

tom view quarter circle we shall not have enough points to definitely locate the joint line on front view A, so we must again make use of the "auxiliary lines."

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