In designing a shaft, hub, and key for a system, which is typically the weakest member?

• A. Shaft
• B. Hub
• C. Key
• D. All are equally strong

Answer: (C)

In mechanical systems involving shafts, hubs, and keys, the key is typically designed to be the weakest member. This choice is intentional, as the key serves a specific function: it is responsible for transmitting torque between the shaft and the hub while allowing for easier failure or replacement in the event of overload situations.

The design philosophy behind this choice is that if one component must fail due to excessive loads or stress, it should be the key rather than the more critical components like the shaft or hub. The shaft and hub are generally designed to withstand higher loads and stresses because they play a vital role in maintaining the integrity and functionality of the whole assembly. When a key fails, it prevents damage to the more substantial components and allows for simpler repair without the need for complete system disassembly.

In summary, the design engineers prioritize protecting the integrity of the more critical elements of the assembly by allowing the key, which is intended to be weaker, to fail first. This ensures that maintenance and repairs can be carried out conveniently while preserving the overall system's reliability.