Fig. 55.
Bevel-gear wheels are employed to transmit motion from one shaft to another when the axis of one is at an angle to that of the other. Thus in [Fig. 55] is shown a pair of bevel-wheels to transmit motion from shafts at a right angle. In bevel-wheels all the lines of the teeth, both at the tops or points of the teeth, at the bottoms of the spaces, and on the sides of the teeth, radiate from the centre e, where the axes of the two shafts would meet if produced. Hence the depth, thickness, and height of the tooth decreases as the point e is approached from the diameter of the wheel, which is always measured on the pitch circle at the largest end of the cone, or in other words, at the largest pitch diameter.
The principles governing the practical construction of the curves for the teeth of the bevel-wheels may be explained as follows:—
Fig. 56.
In [Fig. 56] let f and g represent two shafts, rotating about their respective axes; and having cones whose greatest diameters are at a and b, and whose points are at e. The diameter a being equal to that of b their circumferences will be equal, and the angular and velocity ratios will therefore be equal.
Fig. 57.