A wagon axle is a shaft with which one or two of the wagon’s wheels are attached to the wagon itself. Wagons generally have two axles with two wheels each, one axle at the wagon’s front and one at its rear. The rear axle is usually fixed relative to the wagon’s body, but the front axle is sometimes attached via a pivoting joint that facilitates turning. Wagon axles are considered dead or lazy axles — as opposed to live axles — because they’re not used to transmit power to the wheels to move the wagon.
Wheels are very efficient devices used in transportation, but one of the first challenges faced by man in implementing them was the question of how to attach them to platforms or boxes that could carry substantial loads. Axles were developed for this purpose — rods or shafts inserted through the center of a wheel perpendicular to the wheel’s direction of travel. Devices that look like short tubes, called bearings, are attached to the wagon’s body. The wagon axle is fitted through the bearings and then the wheels are mounted on the axle.
A wagon wheel’s hub, located at its center, is an assembly designed to secure the wheel to the wagon axle. At the center of the wheel is a hole, usually lined with steel or iron. The wheel is mounted on the axle’s end, which itself is generally lined with a thin sheet of steel or iron. Collars are then mounted on the inside and outside of the wheel and bolted to the wheel and axle, securing the wheel. This particular axle design, called a wheelset, calls for the wagon axle and both wheels to rotate at the same speed.
Wheelsets have an inherent design problem, however. When the wagon is turning, the wheels on the outside of the turn must travel farther than the inside wheel. The wheels, then, will slip and skip over the surface on a turn, depending on which has the better traction, leading ultimately to structural damage. In powered vehicles, this problem is addressed by the differential gear, which permits two wheels on an axle to rotate at different speeds. More advanced wagon designs address the problem by letting the wheels rotate independently of each other.
Independent wheel rotation can be accomplished by fixing the axle; that is, securing it to the wagon’s body so it can’t rotate at all. The axle then can be a single shaft connecting two wheels, or two short shafts connected to the wagon’s body independently of each other. The bearings are built inside the wheel hubs, so that they rotate around the fixed axle.