Calc Gear Ratio: Helical/Spur Gears

In summary, the conversation discusses how to calculate the gear ratio and overall reduction ratio of a given arrangement of gears. The input gear is helical and the output gear is a spur gear, and the number of teeth for each gear is specified. The gear ratio is an angular rotation ratio and when the gears are on the same axis, the ratio is 1. It is necessary to multiply the individual ratios of the gears to get the overall reduction ratio, which was calculated to be 83 to 1. However, there are some discrepancies with the given information and further clarification is needed.
  • #1
namith11
26
0
http://C:\Documents and Settings\design3\Desktop\piccs
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!
View attachment 66498
 
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  • #2
Gear ratio is an angular rotation ratio.
When on the same axis, rotations are the same and therefore gear ration is 1 .
Numbers of teeth is not useful for this calculation, but should be coherent.
 
  • #3
Hey,
So if i want to calculate the overall reduction ratio of the system, i will have to multiply the individual ratios of the gears won't i? I can then get my overall ratio. I am not if this is the right way of going about it though! This way, i got the overall reduction to be 83 to 1. But i can't be suree :(
 
  • #4
Hey,
So if i want to calculate the overall reduction ratio of the system, i will have to multiply the individual ratios of the gears won't i? I can then get my overall ratio. I am not if this is the right way of going about it though! This way, i got the overall reduction to be 83 to 1. But i can't be suree :(
 
  • #5
Did you draw this or is it a real question?

I'm assuming you have the diameter, but what is i?
 
  • #6
hey Chris,

Its a real Gear box. I drew the sketch up to calculate the gear ratio. Its an old motor. I know what the motor specs are, but i don't have the reduction ratio and hence I am trying to calculate it. i is the number of teeth. In the diagram, the diameter and number of teeth for each gear is specified.
Thanks
 
  • #7
hey Chris,

Its a real Gear box. I drew the sketch up to calculate the gear ratio. Its an old motor. I know what the motor specs are, but i don't have the reduction ratio and hence I am trying to calculate it. i is the number of teeth. In the diagram, the diameter and number of teeth for each gear is specified.
Thanks
 
  • #8
Well something doesn't make sense then, as the i and d should be the same ratio between a gear pair. Or it's a totally unrelated diameter.

For gears to mesh they need to have the same module.
http://www.tech.plymouth.ac.uk/sme/desnotes/gears/nomen1.htm


Each shaft must turn at the same speed, and the 2nd and 3rd inputs are compund gears. This is done to allow larger ratios without having physically huge gears.

There are only 3 ratios:
Input shaft ti layshaft 1
layshaft 2 to layshaft 2
layshaft 2 to output shaft

Ignoting the diameters and using the teeth as correct:

Gear Pair 1: 7:58
Ratio 1 = 8.28
Gear Pair 2: 19:51
Ratio 2 = 2.684
Gear Pair 3: 15:54
Ratio 3 = 3.6

Overall Reduction Ratio = R1*R2*R3 = 80.07
 
Last edited:

1. What is a gear ratio and why is it important?

A gear ratio is the ratio of the number of teeth on two meshing gears. It determines the speed and torque of a gear system and is important because it allows for the transfer of power from one gear to another.

2. What is the difference between helical and spur gears?

Helical gears have angled teeth and are used for high-speed and high-load applications. Spur gears have straight teeth and are used for low-speed and low-load applications. Helical gears also produce less noise and vibration compared to spur gears.

3. How do I calculate the gear ratio for helical/spur gears?

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. For example, if the driven gear has 40 teeth and the driving gear has 20 teeth, the gear ratio would be 2:1.

4. What is the maximum efficiency of a gear system?

The maximum efficiency of a gear system depends on the gear type and the number of stages in the system. For helical gears, the maximum efficiency can range from 94-98%, while for spur gears it can range from 94-97%.

5. How does the gear ratio affect the speed and torque of a gear system?

The gear ratio directly affects the speed and torque of a gear system. A higher gear ratio means a higher speed but lower torque, while a lower gear ratio means a lower speed but higher torque. This relationship is known as the speed-torque trade-off.

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