Shaft design

Home » Mechanical Transmission » Shaft design

A mechanical shaft is a rotating member, usually of a circular cross-section, either solid or hollow, which transmits power and rotational motion.

What are mechanical shafts?

A mechanical shaft is a mechanical power transmission element, usually circular in cross-section, either solid or hollow, which transmits torque and rotational motion from one device to another.

Shaft-design (

Machine elements such as gears, pulleys, flywheels, clutches, and sprockets are mounted on various shaft types and are used to transmit power from the driving device, such as a motor or engine. A vehicle crankshaft is a prime example of a mechanical shaft, as shown in the above figure.

Types of shafts?

Mechanical shafts are broadly categorized into the following four types.

  • Transmission shaft – The transmission shaft is one of the essential machine components that provides the axis of rotation and oscillation and regulates the motion geometry.
  • Axle shaft – An axle is a non-rotating version of a shaft that supports rotating pulleys and wheels but carries no torque. An axle is a static beam and can be analyzed as one supported beam.
  • Spindle shaft – A spindle is a revolving shaft with a fixture for retaining a tool (or workpiece in the case of milling, grinding, or drilling spindle) (in the case of a turning spindle). The spindle shaft is a tool or workpiece support, positioner, and rotational drive.
  • Machine shaft – These shafts are an inherent element of the machine and are located inside the assembly. A crankshaft of an automobile engine is an example of a machine shaft.

Failure modes for shaft design

  • Fatigue failure
  • Force-induced elastic deformation failure
  • Wear failure

Key principles of shaft design

During the design stage of the shaft, the product designer should consider the following key principle.

  • Keep the shaft as short as possible and the bearing supports as close to the load vectors as possible. This will keep the shaft deflection and bending moments and increase resonance and critical speed.
  • Place shaft stress concentration points away from stressed regions of the shaft. Add fillet radii to a smooth surface finish.
  • Only use a hollow shaft if weight is critical.

Shaft design consideration

  • Form, fit, and function, including tolerancing – Within the embodiment of the design during the
  • Shaft material and treatment
  • Shaft deflection and Rigidity – Deflection-based calculation
  • Shaft strength and stress – Strength bases calculation
  • Frequency response and critical speed

Shaft design process

  • Material selection
  • Geometric layout design
  • Stress and strength
    • Static strength
    • Fatigue strength
  • Deflection and rigidity
    • Bending deflection
    • Torsional deflection
    • The slope at bearing and shaft supported elements.
    • Shear deflection due to transverse loading of short shafts
  • Vibrational due to natural frequency
  • Manufacturing method