Fig. 24.

Rule For Striking Out A Cone Or Frustum 24

In a conical surface, there may be economy, sometimes, in having the slant height 6 times the radius of base. For a Circle may be wholly cut into conical surfaces, if the angle is 60°, 30°, 15°, etc.

But there is a greater simplicity in cutting it, when the angle is 60°. For instance, take AC equal to the slant height, describe an indefinite arc AO; with the same opening of the dividers measure from A to B; draw BC and we have the required sector. This would make the angle C equal 60°. This angle may be divided into two or four equal parts, and we should thus have sectors whose angle would be 30° or 15°, which would not make the vessel very flaring. The accompanying figure gives about the shape of the flaring vessel when the angle of the sector is 30°.

Fig. 25.

Rule For Striking Out A Cone Or Frustum 25