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Gears transmit the motion by engaging each other. If the gears are not in mesh properly, they
cannot convey the rotation and power, disabling the work of the mechanism itself. Here, you
can learn how to engage the gears properly.
・
The distance between gears
Since gears are used in mesh, more than two gears are necessary to transmit the rotating
power. They need to be located at the best positions to engage properly. Though a gear has
teeth with tips and depths, just think about it as a circle to make it simple.
It can be easily imagined that the circle is rotating and transmitting the power to the next circle
it touches. The gears just have the teeth on these circles to avoid slipping. Therefore, the
sizes of these circles will show the proper distance between the gears to engage well. This
circle is called the pitch circle and used to indicate the size of the gear. To calculate the
distance, the pitch circle and the module are needed. The module is another way to tell the
size of the gear.
・
The size of gears
The module indicates a size of a tooth. The larger the module is, the bigger the tooth
becomes. If the gears have different sizes of teeth, they cannot mesh each other well. To
make gears work, you need to use the gears with the same module.
The gears shown in figure A have the same pitch circle but a different module. Also the gears
in figure B have the same module but a different pitch circle. From these figures, you can see
that if the pitch circle is same, the gear with a larger module has less teeth, and that if the
module is same, the gear with larger pitch circle has more teeth. The number of teeth, the
pitch circle and the module are all related. This relationship can be expressed by the following
equation.
MODULE
＝
DIAMETER OF PITCH CIRCLE (mm)
÷
NUMBER OF TEETH
The range between gears and module are very important factors for the function of gears.
・
Designing gears
Let’s try to design the gear mechanism using the pitch circle and the module.
First, you need to decide the number of teeth and the module of gears that you will use. You
can just count the teeth, but you need to check the module on the specification manual of
gears.
Here, let’s use the module 0.5 gears with 40 teeth and 60 teeth for instance.
The pitch circle of 40 teeth gear will be: 0.5
×
40 = 20 (mm), and 60 teeth gear will be: 0.5
×
60 = 30 (mm).
The axis must be at the center of the gear, so that the distance between the axes of two gears
can be calculated by adding each radius. 10 + 15 = 25 (mm).
Place the posts for gears at the calculated range and install gears on them. Applying the
machine oil will make gears run smoothly.
2. Mechanism of Gears
