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Splined Shafts Versus Keyed Shafts

December 31, 2018

Splined Shafts Versus Keyed Shafts

Splines are typically used in mechanical drive systems and can be located in rotating devices in our everyday life. Splines are elevated ridges that mesh with grooves in a connecting component resulting in the transfer of torque. Shafts that are splined are usually one component in a number of mechanisms working in a linear motion. Keyed shafts are defined by two features: the shaft and the rotating element which has a key seat. Keyed shafts are usually one system in a number of mechanisms working in rotating motion.


Unlike keyed shafts, splined shafts can reduce torque transmission capacity. Splines also offer a more uniform transfer of torque and provide equal distribution of a load along the teeth sides of the gear. The result is that the splined shaft experiences a longer fatigue life and is more likely to shield against wear and tear. Additionally, different forms of spline ridges or spline teeth can result in a variance in the strength of drive, the capacity to slide, the rotational transmission concentration, and the capacity for misalignment. For these reasons, shafts that are splined are preferred over key shafts.


Splines are usually composed of both internal and external spline. External splines are cut through a milling machine and internal splines are cut through a type of slotting machine. Manufacturing internal splines is limited in comparison to external splines, as accessibility restrictions tend to be more limited. External splines can be manufactured utilizing a range of processes.


Depending on the specificity of the application, splined shafts come in different types:


Helical splines

These splines have equal groove space between teeth forming a helix with the sides parallel or involute. This design is ideal at allowing rotary and linear motion between parts as well as minimizing stress concentrations under a high load.


Crowned splines

Like helical splines, crowned splines also have equally spaced grooves that are involute. However, crowned splines have modified teeth that act as allowance for potential misalignment.


Ball splines

This splined shaft has outer teeth part that have a ball bearing, enabling free linear motion despite high torque.


Parallel key splines

As the name suggests, the equally spaced grooves are parallel in both radial and axial directions.

Parallel key splines can be cut or cold roll formed. Of these two methods rolled splines are 35% stronger, making them suitable for applications requiring accuracy, high strength, while still offering a smooth finish.