Page:Popular Science Monthly Volume 92.djvu/474

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��Popular Science Monthly

��find the correct length by stepping oflf one of the bottom view spaces sixteen times and we will have the pattern for

���Megaphone

Pattern for a mega- phone which con- sists of two cones with ends cut off

��the complete cone. Fourth, to obtain the pattern line for the part that is cut off, set the pencil dividers at F and then along the line F-G at the point where the small cone is joined to the large cone, draw the arc H-K and the pattern is complete. For the small cone, the method is the same, the apex of this cone being marked L and the bottom view marked M.

In the illustration for the funnel, Fig. 4, the methods of developing the patterns are the same as for the megaphone. However the following helpful short cut has been introduced. In all of the patterns demonstrated so far, a full bottom view has been drawn. This is not always necessary and it saves time if one half the bottom view is drawn from the center of the base line, as shown at A. We know that the other half is exactly the same. When this pattern is devel- oped, we also know that the other half of the pattern is the same. The apex of the large cone is marked B and that of the small cone C.

In the last article of this series a method of developing an approximate sphere by means of parallel lines was shown. In that sphere the sections were vertical, in the sphere shown in Fig. 5 the sections

��are horizontal, and the patterns are de- veloped by means of radial lines. The method followed is exactly the same as for the megaphone and funnel. Only the half pattern is shown for segment A and B. The entire pattern is given for C. This sphere may be made of any number of segments, the greater the number of segments the rounder the sphere, and the more difficult the prob- lem will be.

In Fig. 6, the "hopper," we have a real demonstration of development by radial lines. The other problems in this article have been given as a preparation for this one. Suppose w^e need a pattern for a hopper through which miaterial is shoveled into a machine as is roughly indicated in sketch A. The first thing we must do is to see that the hopper is part of a cone. We must then draw the complete cone as is shown, getting the base, apex and altitude. Second, we must draw the full cone and lay out the part needed for the hopper as shown at B. Third, draw the bottom view C, divide into sixteen parts and draw the lines straight up until they strike the base of the cone. Then draw them converging to the apex. Fourth, draw the arc D-E with the apex as the center. Get the true length of the arc by stepping off the sixteen spaces of the bottom view. Fifth, from each of

���Funnel t Fig. 4

A pattern for a funnel is the same as for a megaphone but a short method is used

these numbered points draw a line to the apex. Sixth, comes a part that is some- what difficult to understand. It con- cerns the true and the apparent or false length of some of these lines. The explanation is this: if we measure the

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