Broken Air Ride spindle

[CarlC]

But I saw no indication of any abnormality with the bearing or race.

There will be no indication of insufficient cornerform radius on the bearing rings. The only time it MIGHT show up on the rings is if the cornerform was too big and did not allow them to properly seat against the spindle shoulder.

Do you have an Rmin and Rmax specified for the cornerform radius? Unless both are specified it is left up to the manufacturer to what this Rmin value will be. Given that it is easier to use a simple turning tool with a small-radius cutting face vs. a true Rmax tool, often the manufacturer without having the specification or an inspection process to verify proper sizing is left to do what is the cheapest.

The Rmin value must be chosen by the design engineer to maximize strength within the confines of manufacturing capability. However, cornerform radii is an easy thing to do vs. keeping superprecision tolerances.

Since it was not mentioned in the other posts my concern would be that there may be spindles with an insufficient cornerform radius. Even if the spindle was properly heat treated the possibility of catastrophic failure significantly increases when a high stress-riser is introduced. Crack initiation and propagation can quickly follow even in low-load and low-cyclic conditions.

I can't tell you how many shafts I've seen, and had the displeasure to inform the customer, that this type of situation could have been easily avoided.