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Merits And Demerits Of Spur Gears

September 27, 2022

Merits And Demerits Of Spur Gears

Spur gears are one of the most popular types of gears used in many industries today.  They are used in various applications, from small toys to large machines. Before exploring the advantages and disadvantages of using them, it is important to understand what spur gears are.


What are spur gears?


Spur gears are machine gears that have straight teeth and are parallel to the shaft they are mounted on. These gears are used when speed reduction is necessary and when there is a need for high precision.

This type of industrial gear is simple, efficient, and relatively inexpensive to produce. However, they also have some disadvantages that should be considered before using them in a particular application.

One advantage of spur gears is their simplicity. They consist of a cylindrical shaft with gear teeth cut into the outer circumference. The teeth mesh with corresponding teeth on another gear, which causes the two gears to rotate in opposite directions. They are very efficient in transferring rotational motion and can be used in a wide variety of applications.

Another advantage of spur gears is their low cost. They can be produced quickly and easily with minimal tooling requirements. This makes them a preferred choice for many applications where cost is a major factor.

There are also some disadvantages to spur gears that should be considered before using them. One disadvantage is that they are not well suited for high-speed applications. The teeth on a spur gear tend to wear down quickly when subjected to high speeds, which can cause the gear to fail prematurely. 

How do spur gears work?

A spur gear is one of the most common types of gear used in industry. They are used to transmit motion between two parallel shafts and can be found in a wide variety of machinery. While spur gears are very versatile and widely used, it is important to understand their types before understanding how they actually work.

Following are the main types of spur gear:



External: An external gear has teeth cut on the outside of the cylinder. The teeth of external gears point away from the centre of the gear. One of the best things about an external gear is that it meshes with both external and internal gears.

Internal:  An internal gear has teeth cut on the inside of the cylinder or gear blank and its teeth point towards the centre of the gear. An interesting phenomenon to be noted is that when two external gears mesh together, they move in opposite directions. Meanwhile, when an external gear meshes with an internal gear, they move in the same direction. 

Rack & Pinion: Rack and pinion is a linear variation of a spur gear. The spur racks have an infinite radius and are used for a wide range of applications. The pinion is a circular gear that engages the linear gear (rack). When rack and pinion engage, linear motion is generated from rotational motion. Mountain railways, steering, and stairlifts make use of rack & pinion gears.

Now, to explain how a spur gear works, it is essential to understand that it is a cylindrical gear with parallel and coplanar shafts. The teeth of this gear are involute, making it one of the most popular involute gears used in industries. The teeth of an involute gear have a specific shape, based on the involute curve of a circle.

The involute is defined as a function drawn by the end of a string as it unwinds from a circle. If you were to draw a line along the path of an unwinding string on a circle, you will get an involute curve. Spur gears are designed based on this principle, thus ensuring a smooth transmission. The torque is transferred from the base circle of one gear to the another with the help of gear teeth 

A spur gear’s tooth meshes only one at a time. Based on the application, a small gear will increase the torque and reduce the speed of a bigger gear. Meanwhile, a larger gear driving a smaller gear will decrease its torque and increase the speed. This flexible application makes these gears a part of everything from bicycles and washing machines to train and aeroplane engines.

Overall, spur gears are a versatile and widely-used type of gear. They have some advantages and disadvantages that should be considered before choosing them for an application. They can provide years of trouble-free service when used in the right application.

Advantages of spur gears

  • There are many advantages to these gears over other types of gears. 
  • A spur gear is very strong and durable and can handle a lot of wear and tear. It can be used to transfer up to 50,000 kW of power.
  • They also have a high degree of accuracy, which is important in many applications.
  • Additionally, their simple design makes manufacturing easy. They can also be easily mounted with ball bearings.

Disadvantages of spur gears

  • While they are one of the most commonly used types of gear, they do have some disadvantages. 
  • One disadvantage is that they cannot transfer torque between non-parallel axis. 
  • Another disadvantage is that they can cause vibration, which can be an issue in some applications. 
  • Finally, a spur gear is not ideal for high-speed applications.

Where are Spur Gears Used? 
The simple design and effective torque transfer make this gear ideal for a wide range of applications. Let’s take a look at some of the common applications where this simple gear is used. They are a common part of a wide range of machinery, and they are used in a variety of ways. Here are a few examples of where they are used.

1)In clocks
2)In turbines, they are used to turn the blades
3)In pumps, they are used to move water or other fluids
4)In conveyor systems
5)Machining tools
6)In the steel sector, the spur type of gears are widely used in rolling mills and cement units
7)In engines of ships and airplanes 


Spur Gear Terminologies 


We will touch upon certain prominent terminologies associated with spur gears:

- Pitch circle: The point of contact between two meshed gears
- Gear ratio: The ratio of the number of teeth of the driver gear to the number of teeth in the pinion gear
- Addendum: The radial distance of the tooth above the pitch circle. Basically, it is the distance between the radial circle and the addendum circle (the circle at the tip of the teeth)
- Deddundum: Deddendum is the radial distance between the pitch circle and the deddundum circle. The addendum circle is the circle that passes through the bottom of the gear teeth
- Flank: The surface between the pitch circle and the bottom. It is the area that comes in contact with the teeth of the meshing gear.



A spur gear is one of the most commonly used types of gear and they offer many advantages, such as being able to run at high speeds, strength, and durability. However, there are also some disadvantages to this gear type, such as the potential for noise and vibration. Overall, the spur gear is a versatile and dependable option for many applications but it is important to be aware of both its merits and demerits before making a decision. You can rely on True Gear & Spline Ltd. for all your gear needs. We are one of the leading names in gear manufacturing. Call us today to source the best gear in Canada.