One of CouplingCorp’s customers encountered this common problem. Their original shaft attachment device had a set screw to secure it on the shaft. The vibration of the hub on the shaft caused micro-fretting between the set screw and the shaft over time. This small movement created a weak spot on the shaft which eventually caused shaft failure.
Stress Risers in Shafts
In any shafts that carry a high torsional load, a stress riser can be catastrophic. In this particular case, the shaft was also carrying a cantilevered load which added to the stress on the outer surface of the shaft. The micro-cracking that happened at the set screw contact point was enough of a stress riser to cause a full crack even on a shaft running at relatively low speeds.
This is a cautionary tale for any shafts that have surface irritations like this or other intentional features. For example, keyways in shafts are often problematic if the inside corners do not have an appropriate fillet. It’s always good to inspect shaft to avoid surprises.
The customer wanted to find a mechanical device without a set screw which would be easy to install, simple to uninstall, and, most importantly, it had to be customized to fit a unique geometry which supported a bearing. Luckily CouplingCorp was able to create the perfect solution. The Anderson Clamp Hub™ is a mechanical clamping device that has a fully customizable flange which was able to handle a tight tolerance bearing surface.
One distinct advantage of the Anderson Clamp Hub is the ability to access the loading screws from either end as chosen by the user. Sometimes it can be very helpful to access the loading screws from the shaft end side because there is more wrench clearance. With some other keyless devices, loading screws are typically found on the back end of the hub where they can be very close to the bearing housing which leaves very little room for access. In other cases, it can be more helpful to have the loading screws on the other end, which is achievable with the Anderson Clamp Hub. This design freedom gives the user a much more user-friendly device.
By working with CouplingCorp on this application, the customer was able to solve the shaft failure problem. In the process of making that change, they were able to save millions of dollars in warranty parts on their entire installed base.