Gear-Gearing Types,Speed Calculation
Gear or gears are metallic wheels with teeth used to transmit power or energy from one shaft to another. It is also used to change the speed of shafts to either high or low speed and also the running direction of a shaft.
TYPES OF GEAR
SPUR GEAR : This is used for transmitting drive between parallel shaft.
BEVEL GEAR : This is used for transmitting power/drive between shafts at angles. Bevel gears have conical cross-sections to help them achieve their purpose.
RACK AND PINION GEAR : This gear is used for converting rotary motion of the pinion to linear motion of the rack.
When two gears mesh,one is the driver and the other becomes the driven. A gear is a driver gear because the power to drive the system is generated by it, while the other is the driven because it is only being driven, and does not produce power/energy.
TO DEMONSTRATE GEARING
- Take two bottle caps that have rounded edges (coke or pepsi bottle).
- Place them on a flat surface so that the outer teeth of one mesh into the grooves of the other one.
- Hold the first cap down lightly with a finger of your left hand and rotate the second cap with your right hand. Do it carefully so that the second cap will rotate about the first cap.
HOW TO MAKE A SIMPLE GEAR
A normal gear is a complicated device to make.
- A sheet of cardboard paper
- A razor blade or a penknife
- A mathematical set
- Draw three concentric circles and indicate their vertical and horizontal center lines.
- Mark out the diagonals at 45 degrees.
- Then mark out the shape of the gear.
- Shade the shape of the gear.
- Cut out with the aid of a razor blade to produce the gear.
CALCULATING THE SPEED OF GEARS
The speed of rotation of a gear is directly proportional to the number of teeth of the gear. For example the speed of a 5-tooth gear will be twice the speed of a 10-tooth gear.
CALCULATING GEAR RATIOS
It is possible to calculate gear ratios. It is important to note first, that gear ratios depend on or vary according to the vehicle and engine size. When a small gear drives a larger gear,the result is gear reduction. Gear reduction produces an increase in torque/power and a decrease in speed. On the other hand, when a large gear drives a small gear, the result is decrease in torque/power and an increase in speed.
CALCULATING THE DIRECTION OF DRIVES IN GEARS
Change in direction of movement in machines cannot be avoided. Example,cars,trailers and trains must must move in a reverse direction in situations like parking. This change in direction is made possible by gear arrangements that result in reverse movement. When the drive gear and the reverse gear systems are engaged at the same time, the driving shaft rotates in the reverse direction. Then when the vehicle moves backward, it shows the typical arrangement of gears which results in change in direction of drive. Change of direction in machine movement is always made possible by gear. A lathe also uses the gear arrangement.