Why Do Direct Drive Motor Shafts Have a Flat Side

February 7, 2022

Motor Minute™ Technical Tip – Why Do Direct Drive Motor Shafts Have a Flat Side?

Hi, Chris from Regal Rexnord here with your Motor Minute technical tip. Helping you become an HVAC motor pro one minute at a time.

Today’s Motor Minute technical tip is “Why do direct drive motor shafts have a flat side?”

I am sure that most of you know the answer to this question. But I have removed enough blower wheels and fan blades with my pulling tool to know that there are at least a few people that do not.

Blower wheels and fan blades are secured to the motor shaft of a direct drive motor with the set screw in the hub of the wheel or fan.

When this set screw is tightened to the shaft, it displaces metal on the shaft leaving an impression and a burr. The tolerance between the inside diameter of the hub and the outside diameter of the shaft is very small.

If this occurs on the round area of the shaft, this burr will make it very difficult to remove the shaft from the hub.

The flat area of the shaft allows the set screw to secure the hub to the shaft without disturbing the hub.

The previously mentioned wheel or fan blade puller, in my opinion, is an essential tool for all technicians. When properly used, it can remove almost any wheel or blade with a burr on the round area of the shaft or other conditions caused by age and rust.

And that’s a wrap on this segment of Motor Minute technical tips. Remember that we provide motor training and product information in multiple formats including videos, literature, podcasts, articles, of course Motor Minute technical tips and classroom education both online and face to face. All of this industry leading training is available at no charge to HVAC professionals at regalmmu.com. Thank you for taking the time to build your motor knowledge.