# Gear Sizing - So that two different size cylinders have matched surface speeds

• mselak500
In summary: This is because the surface speed of a gear is determined by its pitch diameter and the speed of the gear it is meshing with.
mselak500
I have an application where I need to size gears for a set of cylinders with different diameters, and the surface speeds of the cylinders need to match.

Does the ratio between gears have to equal the ratio between pitch diameters?

This is our first application where the diameters of the cylinders are different. For our application, we need to be able to adjust the space between the cylinders, so we typically subtract .010 from the pitch diameter. Since the pitch diameters are the same, the ratio between the pitch diameters will equal the gear ratio. But when I follow this for cylinders with different diameters, the ratios are no longer the same.

Here is some other information:
Helical Gears
Ratio between the cylinders - 1.200 (22.776 & 27.3312)
Pressure Angle - 20 deg.
Normal diametrical pitch - 8

Thanks,

In this case, the ratio between the gears does not need to equal the ratio between the pitch diameters. Instead, you need to ensure that the surface speed of the two cylinders match. To do this, you will need to calculate the gear ratio based on the desired surface speed. This can be done by taking the ratio of the circumference (or speed) of the two cylinders and then finding the gear ratio between them.

## 1. How do you determine the gear size for matching surface speeds of two different size cylinders?

The gear size can be determined by calculating the gear ratio, which is the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. This ratio should be equal to the ratio of the surface speeds of the two cylinders.

## 2. Can the gear size be calculated using the diameter of the cylinders?

Yes, the gear size can be calculated using the diameter of the cylinders by first calculating the circumference of each cylinder (π x diameter). Then, the gear ratio can be determined by dividing the circumference of the larger cylinder by the circumference of the smaller cylinder.

## 3. How does gear size affect the surface speed of the cylinders?

The gear size directly affects the surface speed of the cylinders. The larger the gear size, the faster the surface speed will be for both cylinders. This is because a larger gear has more teeth, which means it can rotate faster than a smaller gear with fewer teeth.

## 4. Is it necessary for the gear size to be exactly matched for the cylinders to have the same surface speed?

While it is ideal for the gear size to be exactly matched, it is not always necessary. As long as the gear ratio is equal to the ratio of the surface speeds, the cylinders will have matched surface speeds. However, having an exact match will ensure the most precise results.

## 5. Are there any other factors that should be considered when sizing gears for two different size cylinders?

Yes, there are several other factors that should be considered, such as the type of gears being used (spur, helical, etc.), the material and strength of the gears, and the torque and load requirements of the cylinders. It is important to consult with a professional or use gear design software to ensure all necessary factors are taken into account for optimal gear sizing.

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