Calculate Gear Ratio - Helical/Spur Gears

In summary, the gear ratio for the given arrangement in the picture is 80.066 : 1. The ratios of gear pairs are 0.12069, 0.3725, and 0.2777, and the result is (7 * 19 * 15) / (58 * 51 * 54) = 0.0125. The input gear is helical and the output gear is a spur gear, and the helical gear is used for the high speed, low torque input shaft. The slight difference in ratio between tooth count and diameters is due to the use of tip diameters instead of pitch circle diameters in the diagram.
  • #1
namith11
26
0
Hey,
I want to know how to calculate the gear ratio of the given arrangement in the picture. I am not sure of how to calculate the gear ratio of two gears on the same shaft. Also the input gear is helical and the output gear is a spur gear. I have mentioned the number of gear teeth, i hope that is enough. I am very confused. Please help!
gearbox1.jpg
 
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  • #2
If I read it correctly, the ratios of gear pairs are;
driver : driven
7 : 58 = 0.12069
19 : 51 = 0.3725
15 : 54 = 0.2777
The result is ( 7 * 19 * 15 ) / (58 * 51 * 54 ) = 0.0125
or 80.066 : 1

Helical gears behave the same as spur gears. Helical gears are quieter at high speeds so they are used here for the high speed, low torque, input shaft.
 
  • #3
The diameters in your diagram appear to be tip diameters not pitch circle diameters which explains the slight ratio difference between tooth count and diameters.
 

What is gear ratio?

Gear ratio is the ratio between the number of teeth on two gears that are meshed together. It represents the number of revolutions the smaller gear must make to complete one revolution of the larger gear.

How do I calculate gear ratio?

To calculate gear ratio, divide the number of teeth on the driven gear (smaller gear) by the number of teeth on the driving gear (larger gear). For example, if the driven gear has 20 teeth and the driving gear has 40 teeth, the gear ratio would be 20/40 or 0.5. This means the smaller gear must make two revolutions to complete one revolution of the larger gear.

What is the difference between helical and spur gears?

Helical gears have angled teeth that are cut at an angle to the gear's axis, while spur gears have teeth that are cut perpendicular to the gear's axis. This results in helical gears producing less noise and smoother operation, but they also have a lower load carrying capacity compared to spur gears.

How do I calculate gear ratio for helical gears?

To calculate gear ratio for helical gears, the helix angle must be taken into account. The gear ratio can be calculated by dividing the number of teeth on the driven gear by the number of teeth on the driving gear, multiplied by the cosine of the helix angle. This will result in a slightly different gear ratio compared to spur gears due to the angle of the teeth.

Can gear ratio be changed after gears are manufactured?

No, gear ratio cannot be changed after gears are manufactured. The number of teeth on the gears is fixed and cannot be altered. However, the gear ratio can be changed by using different sized gears with different numbers of teeth.

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