What Is a Shaft?

A shaft is basically a rotating part of any machine, having a circular cross-section, which is used to transmit power from one part to another or from a power generating machine to a power absorbing machine. To transmit power, one end of the shaft is connected to the power source and the other end is connected to the machine. Shafts can be solid or hollow as per requirement, hollow shafts help in reducing weight and provide advantages.

Shafts are one of the very important components used in machines. They are used to support rotating parts such as pulleys and gears, which are supported by bearings located in rigid machine housings, and gears and pulleys located on the shaft help to transmit motion.

Many other rotating elements are mounted on shafts by means of keys. They are subjected to bending moments and torques due to the reaction forces of the members supported by the shaft and the torque generated by the power transmission.

Shafts always have a circular cross-section and can be hollow or solid. Shafts can be crank, linear, articulated or flexible, but linear shafts are usually used for power transmission.

Shafts are usually designed as steeply stepped cylindrical rods, so they have different diameters throughout their length, although shafts with constant diameters are easy to produce.

The amount of stress in a stepped shaft varies with its length. Shafts with a uniform diameter are not suitable for disassembly, assembly, and maintenance, and these shafts create complications in fastening the parts mounted on them, especially bearings.

1. Types of shafts

01、 Drive shafts

Drive shafts are stepped shafts used to transfer power from one source to another in machines that absorb power. They are mounted on stepped sections of shaft gears, hubs or pulleys for transmitting motion. Such as overhead shafts, line shafts, sub shafts and all factory shafts.

02、Mechanical shaft

Mechanical shafts are located inside the component and are an integral part of the machine, e.g. the crankshaft in an automobile engine is a machine shaft.

03、Axle shaft

axle shafts shafts support rotating elements, e.g. wheels, and can be mounted in housings with bearings, but the shafts are non-rotating elements and are mainly used in vehicles, e.g. axles in automobiles.

04、Spindle

A spindle is the rotating part of a machine that holds a tool or workspace and is used as the short axis of a machine, e.g. the spindle in a lathe.

2. Materials used for shafts

Shafts are usually made of mild steel. If high strength is required alloy steels are used, such as nickel-chromium, nickel, and chrome-vanadium steels. They are formed by hot rolling and cold drawing and grinding. The materials normally used for conventional shafts are carbon steels of grades 50C12, 50C4, 45C8, 40C8.

The material used for shafts should have the following properties:

The material should have high strength .
 The material should have high wear resistance.
 The material shall have heat treatment properties.
 The material shall have good mechanical properties.
 The material must have a low notch sensitivity factor.

3. Standard dimensions of shafts

Mechanical shafts up to 25 mm in 0.5 mm steps.
 Standard dimensions for transmission shafts - step length:
 25 mm to 60 mm - 5 mm step .
 60 mm to 100 mm - 10 mm steps.
 110 mm to 140 mm - 15 mm steps .
140 mm to 500 mm - 20 mm steps.

For machine shafts, standard sizes are up to 25 mm with 5 mm step lengths. For shafts, standard lengths are 5m, 6m and 7m, but generally 1m to 2m is taken.

4. Stresses in shafts

The stresses induced in the shaft are:

Shear stresses due to torque transmission (torque due to torsional loading) .
 Bending stresses due to forces acting on mechanical elements (e.g. pulleys and gears) and the self-weight of the shaft, which are compressive or tensile in nature.
 Combined stresses due to bending and torsional loads.

The maximum allowable shear stress for design stress is:

56000KN/m2 for the shaft, with allowance for keyway.
 Shaft 42000KN/m2 without keyway allowance.

The maximum allowable bending stress is:

112000 KN/m2 for shaft with keyway allowance.
 84000 KN/m2 for shafts without keyway allowance.

5. Manufacturing of shafts

The shaft is manufactured by hot rolling. The strength of the shafts is higher in cold rolling as compared to hot rolling, but cold rolling leads to high residual stresses which cause deformation of the shafts during machining. The forging process is used to manufacture shafts of larger diameters.

After rolling is completed, the shafts are end-machined, with one end of the shaft mounted on a check and the other end of the shaft supported by a lathe turret. For finishing the shaft, the tool is fixed in the tool holder and when the power is turned on, the chuck starts rotating the shaft.

Micrometer is used to check the concentricity of the shaft before machining and customize CNC turning, facing, grooving, taper turning and many other operations according to the usage. Applications such as high volume and CNC are best suited for final machining processes. Machining can also be done with CNC double-ended machines where the shaft is clamped between the tool rotation and the fixture.

To achieve concentricity and roundness, the rotating tools should be opposite each other at the centerline. Drive shafts and motors are usually manufactured using this process.

6. Shaft Transmission

We know that shafts are used for power transmission, so the equation used to calculate power transmission is: P = 2πnT/ 60 . Where P is the power transmitted (W); n is the revolutions per minute (RPM); and T is the torque in Nm.

Speed of shafts used for various applications:

Mechanical : 100~200
 Woodworking machinery: 250~700
 Textile: 300~800
 Light machine shop: 150~300
 Sub-shafts: 200 to 600

7. Shaft design

Shafts can be designed through two different processes depending on the loads to be considered:

01. Strength-based shaft design Transmission shafts are usually susceptible to bending moments, torsional moments, axial tensile forces and their combinations. Typically, bearings are subjected to combined loads of torsional and bending stresses.

Bearings are subject to tensile stresses: tensile stress = P/A. where A = (π/4) x D2 and D is the diameter of the shaft in mm.

Bearing subjected to bending moment: Bending stress = (MbxY)/ I. Where, Mb = bending moment; Y = D/2, where D is the diameter; I = moment of inertia = (πxD4)/ 64

Bearing subjected to torsional moment: Torsional stress = Mt x R/J. where, Mt = torsional moment; R = D/ 2, where D is the diameter; J = polar moment of inertia = (πxD4)/ 32

02. Shaft design based on rigidity

A drive shaft is said to be rigid on the basis of torsional stiffness if the shaft will not twist too much.

{Mt/J} = {(G x ө)/ L}. Where, Mt = torque in N in mm; J = polar moment of inertia = (πxD4)/32; D = diameter of the shaft in mm; ө = angle of torsion; G = modulus of stiffness N/mm2

8. Advantages and disadvantages of shafts

Advantages of shafts:

They are less likely to jam .
 They require less maintenance than chain systems.
 They have high torsional strength.
 They have high values of polar moments of inertia.
 They are very robust and unlikely to fail.
 Hollow shafts have a hollow internal shape, so they require less material.
 Hollow shafts are lighter than solid shafts for the same torque transmission value.
 They have a high radius of rotation.

Disadvantages of shafts:

They have power losses due to loose coupling.
 They vibrate during rotation.
 They generate constant noise.
 Higher manufacturing and maintenance costs.
 Manufacturing is difficult.
 It is not easy to change the speed of the shaft.
 Downtime is long due to mechanical problems.
 Oil dripping from elevated shafts.
 The use of flexible couplings (e.g. leaf spring couplings) results in a loss of speed between shafts.
 If the shaft fails, it takes a lot of time to repair.

In today's article, we take an in-depth look at the different types of shafts, materials, stresses, manufacturing and design, and their importance in machinery and industry. Shafts play a key role in connecting and transmitting power as the rotating part of a machine, so they must be designed and manufactured with careful consideration and engineering practices.

As a precision manufacturing company, Richconn specializes in providing high quality precision CNC milling services and custom sheet metal services. Our team of professionals has the experience to meet your specific needs and ensure that the shafts provided meet the highest standards. If you're looking for a reliable partner for your fabrication needs, consider Richconn and we'll be happy to provide you with exceptional service.

If you have any questions about shafts or other fabrication services, or are interested in our services, please feel free to contact us. We look forward to assisting you and working together to drive your project to success. Thank you for reading this article and we wish you success in your future manufacturing endeavors!