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Overview of Spur Gears – Everything You Need to Know

In their most simple form, a spur gear is a circular steel disc with teeth around the perimeter.  Spur gears are probably the most common gears. These teeth work in conjunction with other gears to create a rotation.  The “toothed” edges cause these gears to look like a spur on the back of a cowboy’s boots. The gears are mounted on shafts that stand parallel to another, and this allows the spur of the first gear to interlock with the spurs of the second and create a rotation.

Spur gears are used in many industries, from the tiny gears in an analog watch, to the complex assortment in a car or aircraft engine, and up to the mechanics behind the world famous Big Ben in London.  These types of gears are all around us.

Definitions and Terms Associated with Spur Gears

Ratio: the ratio is determined by the number of teeth in a pair of gears.  For example, a 2:1 ratio exists if a device contains two gears, and one gear has two times the teeth of the other.  

Gear Trains: gear trains are made of multiple gears. Gears run together in multiple sets to reduce or increase the speed of the drive.

spur gears in a machine

Gear reduction: this is an arrangement of gears in which the speed can be lowered for a slower output.

What Does A Spur Gear Do? 


As mentioned earlier, spur gears are used in a myriad of industries, and at IPG we manufacture a wide range of spur gear types and sizes for various industries including agriculture, automotive, automation, robotic, food processing, and 3D printer equipment, just to name a few.

Anywhere you see a motor or some type of rotation, there are likely spur gears involved. Common applications for these gears are to increase or decrease the speed of the rotation, to reverse the direction of the rotation, to maintain a synchronized rotation between two axes, and to move rotational movement from one axis to another.

Understanding the concept of the gear ratio mentioned before is important.  If one gear is spinning at a rate that is twice as fast as the second gear, this is a result of the ratio between the gears.  In the example given above, if the diameter (the measurement from one side of the gear straight across to the other) is twice the size of the diameter of the second gear, then this is a 2:1 gear ratio.  The industry calls this a “two to one.”  In application, what this means is that each time the larger gear makes a full rotation around once, the smaller gear makes a full rotation around twice. [1]

How Spur Gears Help Alter Operating Speeds

If both gears had the same diameter, they would rotate at the same speed but in opposite directions. However, to increase or decrease speed, gears are often connected together in gear trains.

In a gear train, multiple gears of various ratios are joined together. Each gear turns at a higher rate than the gear before it.  This enables rotations in your designated time to increase at incredible speeds in a relatively simple process. 

For example, in the diagram below, four gears are in a gear train. In this gear train, the smaller gears are one-fifth the size of the larger gears. So, if you connect the second gear to a motor (1st gear) spinning at 100 revolutions per minute (rpm), the third gear will turn at a rate of 500 rpm and the last and smallest gear will turn at a rate of 2,500 rpm. Similarly, you could attach a 2,500-rpm motor to the smallest and last gear to get 100 rpm on the second gear. [2]

4 Advantages of Spur Gears

Simple and Cost-Effective: Spur gears have a straightforward design with straight teeth, making them easy to manufacture and install, resulting in cost-effectiveness for various applications.

Efficient Power Transmission: The direct meshing of teeth in spur gears ensures efficient power transmission between parallel shafts, minimizing power losses due to friction and providing reliable motion transfer.

Precise Speed Ratio: Spur gears offer a constant speed ratio between the driving and driven shafts, making them ideal for applications requiring precise speed control and synchronization, such as in clocks and precision machinery.

Wide Range of Sizes and High-Speed Capability: Available in various sizes and tooth counts, spur gears can handle high rotational speeds, making them suitable for applications requiring fast and reliable rotational motion.

Disadvantages of Spur Gears

There are some disadvantages to spur gears.  The teeth endure stress, they cannot transfer power or energy over long distances, they are typically very noisy, and they require parallel axes to function. [3]

IPG’s Superior Customization Capabilities

Our goal at Illinois Pulley & Gear is to provide you with professional, high-quality, reliable services.  We manufacture a large variety of high-quality, made on demand, timing pulley stock and all the necessary spur gears. We are virtually unlimited in the variety of services we can provide from gears to your full-functioning pulley system.  IPG can produce stock or made-to-order timing pulleys with any of the tooth profiles listed here. Note: HTD, GT, and GT2 are registered trademarks of the Gates Mectrol Corporation.

We want to be your go-to resource for all of your customization needs, and we want you to have the peace of mind that your projects are in good hands.  Click here to contact us with more information about our complete offerings or to receive a quote for your next project.