Shaft failure

[RuralSpaceman]

Been there too. Seems to be a design problem - happens often on small bore shafts with long spans. Shaft will "whip" with the smallest amount of fan unbalance.

If you can't have the fan (shaft, sheave and fan, all together) sent in for dynamic balancing you can try lock-tite (the red stuff) between the shaft and the bearing - then set the grub screws down like described above.

Done both repairs like this; both worked.

[jovusun]

I have seen that before on an air handler back around 1990 where everything "seemed" to be correct. They said blower was out of balance, we replaced shaft, bearings and blower. It didn't repeat itself. We never used loctite back then either, but it sounds like a good idea....

[Octopus]

what i have done was after everything is lined up i would removed the set screw and run a drill down where the set screw goes and drill into the shaft. do not drill the thread for the set screw. I would go no more than 1/8th inch deep. blow out shavings and reinstall setscrew with lock tight. never had one come loose doing this.

Bingo