What is the primary purpose of a woodruff key?

The primary purpose of a woodruff key is to provide a method of securing components, such as gears and pulleys, onto a shaft while allowing for a minimal amount of material removal from the shaft itself. By using a woodruff key, which has a semicircular shape allowing it to fit into a machined recess on the shaft, the design minimizes stress concentration on the shaft by avoiding excessive machining. This helps to maintain the integrity of the shaft and provides a secure fit for the attached components.

While it is true that woodruff keys help in aligning and securing components (which touches on other aspects of the options), the primary benefit they offer is related to reducing the need for extensive machining of stressed areas, thereby preserving the overall strength and performance of the shaft. This unique design helps to distribute the forces more evenly and reduces the likelihood of failure due to stress concentrations.