What is Gear Drive, Gear Train & Spur Gear Drive

In this article, we learn what is gear drive, spur gear drive, and gear train.

What is Gear Drive?

In the case of belt drive, there is a slipping phenomenon that reduces the speed ratio of a system.

In precision machines or mechanisms like the watch gear mechanism, a definite speed ratio is required which is obtained by gear drive or gear wheels.

Gear drive is a positive drive and it is provided when the distance between the driver and follower is very small.

Gears are defined as toothed wheels which can transmit power and motion from one shaft to another shaft by means of successive engagement of teeth.

It is important to note that, both the gears which are engaged, always rotate in opposite directions.

The gear drive consists of two wheels. The smaller wheel is called a pinion and the larger wheel is called a gear. 

Speed ratio or gear ratio

Speed ratio or gear ratio is defined as the ratio of pinion speed to the gear speed.

It is also defined as the ratio of the number of teeth on the gear to the number of teeth on the pinion or it is the ratio of the diameter of the gear to the diameter of the pinion.

Let, ng and np = Gear and pinion speeds in r.p.m.

dg and dp = Diameter of gear and pinion in mm

Zg and Zp = Number of teeth on gear and pinion

Gear ratio or speed ratio = np/ng = dg/dp = Zg/Zp

Spur Gear Drive

Spur gears are used to transmit motion between two parallel axes shafts.

They are the simplest of all gears and the easiest in production.

The teeth of spur gears are cut along the periphery and parallel to the axis of the gear.

Spur gears can be made of steel, brass, other metals, and plastics.

Advantages of Spur Gear Drive

Spur gears are easy to manufacture.

They are made in a variety of sizes from less than 25 mm to several cm in diameter.

These gears are less expensive.

The efficiency of spur gear is high (up to 98 %)

Disadvantages of Spur Gear Drive

Spur gears are not used for high-speed applications.

The operation of the spur gear is noisy.

Applications of Spur Gear Drive

Spur gears are commonly used in machine tool gearboxes, automobile gear boxes, watches, etc.

Gear Train

A gear train is a combination of two or more gears that are used to transmit motion from one shaft to another shaft.

The gear train is necessary when it is required to obtain a large speed reduction within a small space.

The nature of the gear train used depends on the required velocity ratio and the relative position of the axes of shafts.

Gear trains are commonly used in various machines (lathe, milling, drilling, etc.), automobiles, clocks, ships, watches, etc.

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