THRUST OF STRAIGHT–TOOTH BEVEL OR MITER GEARS
When a pair of straight tooth bevel or miter gears runs together, they have a tendency to push each other apart.
This pushing action – thrust – is always backward toward the hub. (See Figure 5.7A)
THRUST OF SPIRAL–TOOTH BEVEL AND MITER GEARS
Thrust is a very important consideration when it comes to the operation of spiral miter gears. Why? With spiral miter gears there is a backward thrust on one gear and a forward thrust on the mating gear (depending upon the rotation direction and gear hand). The sudden stopping of a pair of spiral miter gears causes a momentary reversal of thrust.(See Figure 5.7B)
To prevent the hub of the gear from rubbing against an adjoining surface, thrust bearings or washers should be mounted on the shaft – in back of the hub – to absorb the thrust load.
Since spiral miter gears have both forward and backward thrust – depending upon the direction of rotation – provision must be made to absorb this thrust. Often this is accomplished through the use of combination radial-thrust bearings.(See Figure 5.7C)
