Page:Popular Science Monthly Volume 92.djvu/311

 Simple Designs for Sheet Metal Working

IX. — Development of patterns for approximate spheres By Arthur F. Payne

Former Director of Vocational Education, Columbia University

��THE name "Approximate Sphere," given to the problem illustrated, will very likely need explanation to some of the readers of this series. The common names for this problem are "Gored Ball" and "Slab-sided Ball." A sphere is an object that presents a perfect circle from all points of view. The sphere, shown in Fig. 1, presents a

���A "slab sided" ball is an appropriate ornament as a finial on top of a flag pole, steeple or turret

perfect circle from the front view only, the top view is an "approximate circle," that is, it is almost a circle, being divided into sixteen parts, which are variously called gores, slabs, panels or sections. In this article, these parts will be called "sections," as this is considered the correct name.

The practical application of the prob- lem would be as a finial on top of a flag pole, steeple or turret, or as an orna- ment on buildings.

The interesting feature about this prob- lem is that the methods used are the same as those used in the elbows and tee joints, illustrated in pre\'ious numbers. In fact, to develop the pattern for one of the sec- tions, we must first of all recognize the fact that each section is merely part of a cylinder or pipe. This may seem some- what difficult to see at first, but as the directions are followed and the pattern

��is developed, it will become clear. This particular point is illustrated by G and H of Fig. 2.

There are several different methods of developing the pattern for this problem. For the sake of better understanding and practice, three methods are illustrated. However, as they are worked out, it will be seen that they are all based on the same principle.

The method of obtain- ing the correct front view of the sphere is shown in Fig. 1. This is not abso- lutely necessary to the development of the pat- tern, but is given because it is often useful in mak- ing a sketch for the cus- tomer. To get the cor- rect front view; first, draw the top view A, which is done by dramng a circle of the size wanted and then dividing the circle into the number of sections de- sired. In this case there are sixteen sec- tions. Second, draw the front view B, This presents the problem of drawing the true picture of the section C. We can very easily get the width at the widest part by dropping down the dotted lines as shown in the drawing, but we have to find some way of drawing in the curved

���A short cut method in which no bottom view is required for obtaining pattern

line to complete the section from the front view. This is done by drawing the arcs D and E on the top view. This is for the purpose of locating points on the

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