Overlap ratio or axial contact ratio in helical gears

In summary, the conversation is about the Overlap Ratio (OR) / axial contact ratio of a helical gear pair and the confusion around understanding it. The person is looking for a physical explanation and the effect of OR being less than one. They also request for a PDF copy of QTC's "elements of metric gear technology" and mention that KHK has gear technology references available.
  • #1
k.udhay
160
10
Hi,

I am trying to understand the Overlap Ratio (OR) / axial contact ratio of a helical gear pair. Unlike transverse contact ratio, I am unable to understand OR so easily.
What does it mean if the OR is exactly 1? What will happen practically when it goes less than one? Thanks.
 
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  • #3
Thanks. But this book again tells the OR as a mathematical relation whereas I want to understand it physically. I assume a case where the transverse contact ratio is more than 1 already and want to know the effect when OR is less that one.
 
  • #4
Do you have a pdf copy of the QTC "elements of metric gear technology"
http://www.qtcgears.com/Q420%20PDF%20Files/Tech.pdf
See sections 8.4, 11.4, 17.2.3, 17.4.3 and 21.

KHK have Gear Technology References.
http://www.khkgears.co.jp/en/gear_technology/guide_info.html
 
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Related to Overlap ratio or axial contact ratio in helical gears

1. What is the overlap ratio in helical gears?

The overlap ratio, also known as the axial contact ratio, is a measure of the amount of contact between the teeth of two helical gears. It is calculated by dividing the total length of the contact between the gears by the base pitch of the gear teeth. This ratio is important for determining the load distribution and noise level of the gears.

2. How is the overlap ratio calculated?

The overlap ratio is calculated by dividing the length of the contact between two helical gears by the base pitch of the gear teeth. The length of contact can be determined by measuring the distance between the start and end of the contact area on the gear teeth. The base pitch is the distance between two adjacent teeth on the gear.

3. What is a good overlap ratio for helical gears?

A good overlap ratio for helical gears is typically between 1.2 to 2.0. This means that the length of contact between the gears is 1.2 to 2 times the base pitch of the gear teeth. A higher overlap ratio can improve load distribution and reduce noise, but it can also increase friction and wear on the gears.

4. How does the overlap ratio affect gear performance?

The overlap ratio has a significant impact on the performance of helical gears. A higher overlap ratio can improve load distribution and reduce noise, but it can also increase friction and wear on the gears. On the other hand, a lower overlap ratio can lead to uneven load distribution and higher noise levels. Therefore, the overlap ratio must be carefully considered to ensure optimal gear performance.

5. Can the overlap ratio be adjusted after gears are manufactured?

No, the overlap ratio cannot be adjusted after gears are manufactured. It is determined by the design and manufacturing process of the gears. Therefore, it is important to carefully calculate and consider the overlap ratio during the design phase to ensure the desired performance of the gears.

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