Spur Gears

MECHANISMS GEARS 1. SPUR GEARS - SIMPLE GEAR TRAIN

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A simple gear train uses two gears, which may be of different sizes. If one of these gears is attached to a motor or a crank then it is called the driver gear. The gear that is turned by the driver gear is called the driven gear. Gears are used to increase or decrease the speed or power of rotary motion.

2. SPUR GEARS - IDLER GEAR

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When a simple gear train has three meshed gears, the intermediate gear between the driver gear and the driven gear is called an idler gear. The driver gear and the driven gear will now rotate in the same direction. An idler gear does not affect the speed between the driver gear and the driven gear.

3. MITRE GEARS • •

Mitre gears work in pairs. They are bevel gears of equal size, with the same number of teeth. Mitre gears transmit rotary motion and torque through 90º without producing any change in rotary velocity.

4. RACK AND PINION •

A rack and pinion is used to transform rotary motion into linear motion and vice versa.

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The pinion is a round spur gear fixed to a shaft. The rack is a spur gear with teeth set in a straight line.

PULLEYS AND BELTS 1.VEE PULLEY AND BELT •

One method of transmitting force and rotary motion from one shaft to another is by using pulleys and belts.

2. STEPPED CONE PULLEYS • •

Machines such as pillar drills and centre lathes operate with a variety of output shaft speeds. One way of achieving this is by using stepped cone pulleys. Speed settings are changed by altering the position of the Vee belt. This is done manually with the machine isolated (disconnected) from the mains electricity supply.

SPROCKETS AND CHAIN 1. SPROCKETS AND CHAIN • • • •

Sprockets and chains are used when no slip, i.e. direct positive drive, is essential. E.g. on a bicycle or motor bike. Sprockets are toothed wheels attached to the driver and driven shafts. Chains consist of many loosely jointed links which engage with the sprocket teeth. It is important that the chain is tensioned correctly to prevent it becoming disengaged from the sprockets. The speed of a sprocket and chain system is determined by comparing the number of teeth on each sprocket.

CAMS AND FOLLOWERS 1. PEAR SHAPED CAM • •

A cam is a specially shaped piece of metal or hard wearing plastic, which is usually fixed to a rotating shaft. As the cam rotates the follower moves up and down in a reciprocating motion.

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The distance and speed at which the follower moves depends on the shape of the cam.

LIFTING SYSTEMS 1. SINGLE & MULTIPLE PULLEYS •

By increasing the number of pulleys in the animation you will see that it is possible to lift heavier weights using the same amount of effort.

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This is useful as it is easier to lift something by pulling downwards rather than upwards. In order to raise the load the effort force has to be equal to or just greater than the load. There is no mechanical advantage when a single pulley is used.

LEVERS 1.CLASS 1 LEVER •

This type of lever has the fulcrum positioned between the effort and the load. The effort force can be magnified or diminished depending on the position of the fulcrum between the effort and the load.

2. CLASS 2 LEVER •

This type of lever has the load positioned between the effort and the fulcrum. A Class 2 lever always magnifies the effort force because it is always positioned at the opposite end of the lever from the fulcrum.

3. CLASS 3 LEVER •

This type of lever has the effort positioned between the load and the fulcrum. When this form of lever is operated the effort force always diminishes but the distance moved is magnified.

Exercise Read and understands the notes and textbooks from page 55 to 59. Referring to your notes and textbooks, for each of the mechanisms (i.e a. VEE PULLEY AND BELT b. STEPPED CONE PULLEYS

c. d. e. f.

SPROCKETS AND CHAIN CAMS AND FOLLOWER LIFTING PULLEYS CLASS 1, CLASS 2 AND CLASS 3 LEVERS

Sketch at least one real life application/usage and explain how it works pertaining to the sketch you’ve shown.