What Is Idler Gear? Why It Is Important?

Gear mechanisms are one of the most important parts of mechanical design. Designing gear systems is not an easy thing to do. The designed gear system must provide the required input and output torques and velocities. Also designed gear system must comply with constructional restrictions defined by the placements of other mechanical elements such as shafts.

One of these constructional restrictions in the direction of rotation requirements of shafts. When you are designing a gear train system, you must also consider the rotation direction of your output shaft. So, the rotation direction of your input shaft is also very important.

Why Idler Gears Are Used?

Illustration of idler gear(Image Source:

If you use idler gears inside your gear systems, you can also monitor the rotation directions of shafts. As you see in the illustration above, if an idler gear is used between driven and driving gears, the rotation directions of them are the same.

Applications of idler gears in gear trains are very common. In gear train torque and velocity ratio calculations, idlers are not considered. Because you need to add idlers both in numerator and denumerator of teeth number equation.

Construction requirements can also require the use of idler gear. If the distance between two input and output shafts is high, you can use idler gears between driving and driven gears.

Use of idler gear inside a gear train(Image Source:

Because of these reasons, the use of idler gears is very common in engineering practice.

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