Thursday, 5 June 2014

There are certain important considerations to be made when selecting a gearbox. Here we reveal what to look out for so you make the right choice.

Gear ratio

This means the correlation between the amount of teeth on different gears. For example, if one gear has 39 teeth while another has 13, the gear ratio would be 3:1. When there are more than two gears, you need to calculate the ratio between each pair and multiply them. So if there were three gears, with 16, 12 and eight teeth respectively, the calculation would be as follows:
16/12 = 1.33
12/8 = 1.5
1.33 x 1.5 = 1.995
Therefore, 1.995 would be the overall gear ratio of this system.

Output torque

If you require a high output torque, select a large gear ratio as this will lower the output shaft speed of the motor. Torque and speed are inversely proportional, so if you’re using a lower gear ratio then a smaller output torque would be achieved.

Speed (rpm)

Speed is proportional to gear ratio, so a higher ratio results in greater rpm and vice versa. To calculate output speed, divide the input speed by the gear ratio.

Gear arrangement

The more efficient the gear arrangement, the more energy it will allow to be transmitted and converted into torque. Different gear arrangements, such as spur, helical, bevel, worm, hypoid and cycloid, offer varying levels of efficiency depending on the application.


Backlash refers to the lost motion in a mechanism caused by gaps between parts, in our case the clearance between gear teeth. Some ‘play’ is required between teeth, to allow for factors such as lubrication and thermal expansion. However, excessive backlash can send shocks through the whole gear system which may damage teeth and other components. In some precision applications such as robotics and automation, achieving the right degree of backlash is essential to guarantee accuracy.
For all the advice and information you’ll ever need, get in touch with the friendly Transmission Systems team here at Gibbons - our expertise will help you make the right choice. Call 01621 868138 or email and we’ll be happy to help.


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