What’s Radial Force?

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Radial force is a force acting in a straight line perpendicular to the centerline of an object traveling in an orbital path, keeping it on a uniform orbit. It is important for designing tools and objects with rotating parts, such as bearings and power tool bits. Excessive radial force can lead to wear and failure. Radial force variation occurs when the momentum of the object changes during operation, presenting challenges for designers.

Technically, a radial force is any force acting in a straight line. In physics, it is often used to describe the influence exerted perpendicular – at right angles – to the centerline, or axis, of an object traveling in an orbital path. Simply put, a ball swung in an arc at the end of a piece of string will experience this force, keeping the string taut. Several other predictable forces work in different directions to keep the ball spinning through the arc, but the radial force is responsible for pulling it away from the string hand.

While the exact origins and nature of radial forces are highly complicated, they can be seen at work in many everyday processes, such as in power tool bits, rotating car tires, and bearings. In machining, this force is explained as the influence that pushes a cutting tool away from the surface to be cut. Correctly calculating radial force specifications is a critical step in the design of tools and other objects with rotating parts.

What does the radial force do?
Radial forces are an important component of the process that keeps any object traveling in a circular orbit. When a known mass (such as a ball) rotates in a circle a predetermined distance (the radius) from the center point at a constant speed, radial force pushes the mass out, away from the center. The force keeps the rotating mass the same distance from the center point, maintaining a uniform orbital path: a circle or an ellipse. Without the action of this force, the course would be irregular and unpredictable.

This is true for all objects in orbit, whether they are physically attached to the center or not. A loose ball spun inside a bucket is also pushed against the inside wall of the container by a radial force. Radial forces, for example, are also responsible for holding a roulette ball against the edge of the wheel’s slot as the wheel spins.

Why are radial forces important?
Accurate calculation of radial forces is a critical design consideration of anything that exhibits orbital motion. For example, accurately establishing the magnitude of this variable plays an important role in the overall efficiency, safety and life of an equipment. It also allows designers to understand what the practical limitations will be for a given item.

For example, bearings are widely used in many different types of equipment to support, guide, and reduce the friction of motion between the stationary and moving parts of the machine. They are often exposed to radial forces which create internal stresses in the material which can lead to wear and eventual failure if the force and associated stresses become excessive. Bearings must be strong enough to withstand the pressures that are regularly applied to them. For this reason there are types of bearings specifically designed and calibrated for mechanical applications characterized by high radial forces.
Another example of this phenomenon in the workplace is the force a cutting tool experiences when it removes material from the surface of a workpiece. The force acts on the tool to move it away from the workpiece. The amount of force acting on the cutting device will depend on the characteristics of the tool itself and the properties of the material being cut. If the tool is poorly designed and experiences excessive radial force, it could make it very difficult to drive the cutting edge into the workpiece, resulting in sub-standard results or even potentially injuring the operator when the tool is pulled away.

Radial force variation
A variation of this phenomenon occurs when the momentum of the traveling object changes or evolves during operation. Known as a change in radial force, it can be illustrated using the example of an automobile tire. The tire will experience a radial force in a direction perpendicular to the wheel axis which, if the tire were perfectly round and the road surface perfectly smooth, would remain the same as the wheel rotates. However, this is not the case, so the radial force exerted on the tire changes each time it rotates. This presents designers with challenges when designing the equipment, as they must be able to operate safely in constantly changing environmental conditions.

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