What Are Casters?
Most of us use casters every day without being aware of it. They allow your chair to move across the floor in any direction. They are the wheels on the front of the grocery cart that go wherever you point them with just a push. While the wheel gets credit for being one of human kinds best and earliest inventions, the caster was not patented until the late 1800’s by David Fisher. Even today new styles of casters are being developed like the “Omni Directional Caster”.
Early casters were simply u-shaped frames holding a wheel and axle together. The wheel was fixed, it simply went in forward or back, and was not “steerable”. So the next development was to put a bearing on top of the frame to allow the wheel to pivot. This was better than a fixed wheel, but the wheel sometimes skipped sideways without pivoting. There was no reason for a wheel to spin in the direction of the force, especially If the wheel and floor were smooth. What makes the modern caster do its magic is the fact that they are not only easy to pivot but they align and continue in the direction they are pushed. Because of this “self-centering”, or “self-steering” material handling and movement forever.
Fixed & Rotating Casters
Fixed and rotating casters have a common feature. The axle holding the wheel is centered under the mounting or pivot point. A self-steering caster has the mounting point of rotation offset from the axle. It is this offset that gives casters their unique properties. This offset means that the caster can be pointed in any direction and follow the direction of any force on it. The offset of the pivot point means that friction on the side of the wheel pushes it to where rolling resistance is less than the side load. Depending on their diameter casters require very little rotation to align with the direction of force. So, there are hundreds of styles of caster made in different materials, wheel styles, and sizes.
If there is a better example of simple genius in humankind, one would be hard-pressed not to submit the caster as one of them.