How Do You Determine Gear Tolerance and Surface Roughness?

[hanson]

Hi all.
How do one design the gear tolerance and the surface roughness of a gear?
I know there are some quality numbers in AGMA, but is quotaing the number is enough for specifying the tolerances of a gear?

about the surface roughnessm i saw many things like remove mostly 3.2mm etc...How do i decide all these?

 

[FredGarvin]

I know you're not going to like this answer, but ...it depends. This is a pretty specialized field that has a lot of independent research conducted. You really need to be around someone experienced in the specification of gears.

Let's put it this way...you have a general area that the gears are going to operate in as far as speed, load and possibly accuracy of loaction (i.e. stepper motors, motion control). Things like AGMA quality will be referenced off of your judgement of how imprtant these things are. Obviously, the balance is going to be the requirements of the design and the cost of making the gears. If you are running low speed and relatively low power, then something off the shelf, forged/cast would probably do you just fine. However, if you start to have to look into actually specifying a gear for manufacture, there's a lot that has to be considered.

You, as the designer, have to look at the overall design. Can you live with a lower tolerance in the gear, i.e. can your stack ups, etc... handle having a less controlled profile? Can you handle possibly greater runout and backlash? Things like surface roughness will effect the effectiveness of the lubrication as well as the noise generated by the gears. It can also effect the strength of the gear teeth and their longevity. Can you live with a bit more noise? Do you have sufficient cooling? It goes on and on.

I can tell you that, in my applications, we don't look below AGMA 7 and more frequently specify 10. However, we do high speed applications with extremely tight tolerances. We also have to have a long lasting gear so that also includes a lot of secondary machining and possibly plating processes.

Are you in the position to sit down with someone who has experience with gears, that can take a look at what you are doing? If not, can you post what your objectives are?

 

[ravenprp]

Designing gear tolerance and surface roughness is a critical aspect of gear design that requires careful consideration and understanding of the application and manufacturing process. The AGMA (American Gear Manufacturers Association) provides guidelines and quality numbers for gear tolerances, but simply quoting these numbers may not be enough to specify the tolerances for a gear.

When determining gear tolerances, it is important to consider factors such as the gear's function, the expected load and torque, and the manufacturing process. For example, if the gear will be used in high-speed applications, tighter tolerances may be necessary to ensure smooth operation and reduce noise and vibration.

Similarly, the surface roughness of a gear is also dependent on the application and manufacturing process. The AGMA provides guidelines for surface roughness, but it is important to also consider factors such as the type of material used and the type of gear tooth profile. For example, gears with involute tooth profiles may require a smoother surface finish compared to gears with cycloidal tooth profiles.

To decide on the specific tolerances and surface roughness for a gear, it is best to consult with a gear design engineer or a manufacturer who has experience in designing and manufacturing gears for similar applications. They can provide valuable insights and make recommendations based on their expertise and knowledge of the manufacturing process.

In addition, it is important to conduct thorough testing and inspections of the gears to ensure that they meet the specified tolerances and surface roughness requirements. This will help ensure the gears perform as intended and have a longer lifespan.

In summary, designing gear tolerance and surface roughness requires a combination of understanding the application, consulting with experts, and conducting thorough testing and inspections. Simply quoting numbers from AGMA may not be enough to specify the tolerances and surface roughness for a gear.