ID Fan Shaft Diameter

If you apply some knowledge and imagination to this "problem," you might think of some possibilities on your own.

You can. The OEM spec it out like that to the motor manufacture. You can do the same.

I know there is a language barrier here at times and it makes it hard to know what is being really ask about. If I read this correctly it seem there is a step in the shaft that your questioning for some reason. Did you have a failure at this step or are you just curious as to why this was done.

In some cases the step is done because the torque on the shaft from motor allows a smaller coupling to be used. The fan or driven unit needs to have the larger shaft due to loads or other issues. This is not un-common to see. Ask the manufacture why they had elected to provide this on that unit. This will give you a much more complete answer to your question.

If ever you've had the misfortune to see the aftermath of a fan shaft shear it becomes obvious.

Maybe one end only supports the radial loads of the impeller (NonDriveEnd) while the oposite (DriveEnd), must take as well the transmision of power from the motor, so it would be the radial loads + torsion. More important during start-up.

Salu2 cordiales,

Abel

The driving end shaft is always bigger diameter for driving the load and the non driving end is usually smaller for cooling fan. Sometime is the shaft is the same and most of the time is not the same size. It depend upon the manufacture and the engineer that design it.