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

[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,

 

[Navin A S]

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.