Shafts: Definition, Types, And Application

What is a Shaft?

A shaft is a fundamental rotating component found in many machines, typically featuring a circular cross-section. Its main role is to transmit power from one section of a machine to another, or between two separate machines—one generating and the other consuming power.

Shafts play a crucial role in machinery by supporting other rotating elements, such as gears and pulleys. These shafts, in turn, are held in place by bearings mounted within the sturdy frame of the machine. In practice, shafts not only transfer power between connected components but also withstand torque from the power flow and bending forces arising from the weights and reactions of the parts they support.

It’s important to differentiate shafts from axles. While both support rotating members, only shafts are designed to transfer power along their length.

Shafts are always manufactured with a circular cross-section and may be either solid or hollow, depending on the application. They come in several varieties—straight, cranked, flexible, or articulated—though straight shafts are by far the most common choice for power transmission.

In many cases, shafts are designed as stepped cylindrical bars, meaning their diameter changes at various points along their length. Although it might seem simpler to produce shafts with a uniform diameter, stepped designs are necessary to account for the differences in stress experienced along the shaft.

Additionally, shafts with a constant diameter can create complications during assembly, disassembly, or routine maintenance. In particular, they can make it more difficult to secure attached parts—especially bearings—since these parts need to be fixed against any movement along the shaft.

When deciding on the dimensions of each step in a shaft, designers ensure that every attached component has proper access to its designated position. This careful consideration helps streamline both the assembly and the long-term maintenance of the machine.

The Material Used for the Shafts

In most cases, ordinary shafts are manufactured using mild steel. However, when the application calls for greater strength, manufacturers turn to various alloy steels, such as those containing nickel, nickel-chromium, or chromium-vanadium. The initial shaping of shafts typically involves hot rolling, after which they are brought to their final dimensions through processes like cold drawing, turning, or grinding.

When selecting materials for shaft production, several key properties are essential. The material must offer considerable strength and allow for efficient machining. It is also important that the material exhibits a low notch sensitivity, responds well to heat treatment, and resists wear over time.

For standard shafts, carbon steels are most often chosen—particularly grades such as 40C8, 45C8, 50C4, and 50C. These materials provide a reliable balance of strength, machinability, and durability for a wide range of mechanical applications.12.

Manufacturing of Shafts

Shafts are commonly manufactured through hot rolling, with their final form refined by methods such as cold drawing, turning, or grinding. Notably, shafts that undergo cold rolling tend to exhibit greater strength compared to those produced by hot rolling, although this process also introduces higher levels of residual stress.

It is important to consider that residual stress may lead to deformation during subsequent machining operations—this becomes particularly evident when features like slots or keyways are added. For shafts with larger diameters, forging is typically the preferred approach, after which the workpiece is further shaped using a lathe.

Types of Shaft

Shafts are mainly classified into two types:

• Transmission shafts are used to transmit power between the source and the machine absorbing power. e.g., countershafts, line shafts, and all factory shafts.
• Machine shafts are an integral part of the machine itself. e.g., crankshaft
• Axle shafts are used in vehicles.
• A spindle shaft is a rotating shaft with a fixture for holding a tool or a workpiece.

The Standard size of shafts are:

The standard sizes of transmission shafts are:

• 25 mm to 60 mm with 5 mm steps
• 60 mm to 110 mm with 10 mm steps
• 110 mm to 140 mm with 15 mm steps and
• 140 mm to 500 mm with 20 mm steps
• The standard length of the shafts is 5 m, 6 m, and 7 m.

The standard sizes of Machine shafts are:

• Up to 25 mm steps of 0.5 mm

Advantages of Shafts:

• The shaft system is less likely to jam.
• Less maintenance than a chain system when a tube is attached to the drive shaft.
• A hollow shaft is a low weight than a solid shaft for the same torque transmission.
• In the hollow shaft, the internal shape is hollow so the materials required are less.
• The shaft is strong and it has a low failure chance.
• High polar moment of inertia
• High torsional strength

Disadvantages of Shafts:

• The power loss is due to loose coupling.
• Shafts can vibrate during rotation.
• Produced a constant noise
• Maintenance and manufacturing costs were high.
• The manufacturing process is difficult.
• The downtime was longer due to mechanical problems.
• The use of flexible couplings, such as a leaf spring coupling, can cause a loss of velocity between shafts.
• Changing the speed was not so easy.
• Oil dripping from overhead shafting.

FAQs.