Shaft-Hub Connection

Shaft-hub connections are essential machine elements used to reliably transfer torque and rotary motion between a shaft and a mounted component (hub), such as a gear, pulley, or flywheel. These connections can be categorized into three main types based on how they transmit power: positive-locking (form-fit), friction-locking (force-fit), and material-locking.

Types of Shaft-Hub Connections
Positive-Locking Connections (Form-Fit)
These connections use a geometric fit to prevent relative movement, transmitting torque via surface pressure on the engaging elements.
Key Connection (Keyway): A rectangular or square key sits partially in a slot (keyseat) in the shaft and partially in a keyway in the hub.
Advantages: Cost-effective, standardized (e.g., DIN 6885), easy to assemble and disassemble.
Disadvantages: The keyway weakens the shaft due to a notch effect, can have backlash with tolerance variations, and is limited to medium torques.
Splined Shaft Connection: The shaft and hub have multiple interlocking teeth (splines) around their circumference.
Advantages: Transmits very high torques, allows for precise positioning and excellent concentricity, and can handle axial movement.
Disadvantages: Higher production and tooling costs than keyways.
Polygon Profile: A non-circular (e.g., hexagonal or octagonal) profile that provides multiple contact surfaces to transmit torque with minimal notch stresses and high precision.
Friction-Locking Connections (Force-Fit)
These connections rely on the clamping force and resulting friction between the shaft and hub to transmit torque, resulting in backlash-free operation.
Press/Interference Fit (Shrink Fit): The hub is heated (or the shaft cooled) and then assembled. Upon returning to room temperature, the interference generates high contact pressure and friction to transmit power.
Advantages: Backlash-free, high torque capacity, even load distribution, minimal notch effect.
Disadvantages: Difficult or potentially destructive to disassemble, complex assembly process.
Clamping Element (Keyless Locking Assemblies): Conical rings are pushed together by tightening screws, creating radial forces that clamp the hub to the shaft.
Advantages: Easy assembly/disassembly, no keyway needed, backlash-free, excellent concentricity, and higher transmissible torques than keys.
Disadvantages: Can be more expensive than positive connections.
Taper Connection: An axial force (e.g., by tightening a nut) pushes a tapered hub onto a tapered shaft, creating a secure friction fit.
Material-Locking Connections
This type involves a permanent bond between the shaft and hub.
Welding or Adhesives: The components are joined using welding, soldering, or industrial adhesives. This is less common in power transmission applications due to repair difficulties.
Key Considerations for Selection
Choosing the right connection method involves balancing cost, ease of assembly/disassembly, required torque capacity, and precision requirements. Frictional connections are often used for high torques and precision applications where backlash is unacceptable, while keyways offer a cost-effective, standard solution for moderate loads.