Spur Gear

When two spur gears of different sizes mesh together, the larger gear is called a wheel, and the smaller gear is called a pinion. In a simple gear train of two spur gears, the input motion and force are applied to the driver gear. The output motion and force are transmitted by the driven gear. The driver gear rotates the driven gear without slipping.

 Bevel Gears

Bevel gears have teeth cut on a cone instead of a cylinder blank. They are used in pairs to transmit rotary motion and torque where the bevel gear shafts are at right angles (90 degrees) to each other.

Why Do Clocks Have Brass Gears?

Brass gears are often used in clocks where they work well without any lubricant. Oil causes dust to adhere to the gears and this causes gear-tooth wear. An advantage of brass gears is that constant meshing work hardens their teeth. Because of this, the brass gears in well used old clocks often show little sign of wear.


Worm and Wormwheel

A gear which has one toothe is called a worm. The tooth is in the form of a screw thread. A wormwheel meshes with the worm. The wormwheel is a helical gear with teeth inclined so that they can engage with the thread-like worm. The wormwheel transmits torque and rotary motion through a right angle. The worm always drives the wormwheel and never the other way round. Worm mechanisms are very quiet running.

 Rack and Pinion

A rack and pinion mechanism is used to transform rotary motion into linear motion and vice versa. A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack.

 Internal Gear

Internal gears have better load-carrying capacity than external spur gears. They are safer in use because the teeth are guarded.


Photo Credits: Mechanisms, by Oliver & Boyd; Publisher, SCDC Publications, Copyright 1993

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