Well, using a PC case fan as a freezer blower seemed like a good idea at the time: it worked, moved an adequate amount of air, and was pretty nearly silent. Until, that is, frost built up on the blades, water froze inside the frame, and the thing began sounding like a stick running along a picket fence:
I replaced the first fan with another having slightly more clearance between the blade tips and the frame, but to no avail.
So I dug the OEM fan (a.k.a., the Freezer Dog) from the heap, dismantled it, and discovered why it was howling. Turns out that the shaft nearest the fan blades was scored inside that bearing:
A closer look:
The rest of the shaft looked fine to me, so I put some green Loctite on rotor at the shaft and shoved the long end of the shaft (using the drill press as an arbor press) to put the scored section inside the rotor:
Yes, that’s the same Loctite ridge you saw there…
The shaft has several small grooves that probably held lubricant or acted as alignment guides or something useful, but I’m hoping none of that matters. The rotor is turning backwards now, too, which shouldn’t make much difference: it’s pretty much symmetrical.
While I had the motor apart, I whacked the bearings with a rod to shrink them a bit:
Slobbered more STP on the bronze bearings, reassembled everything again, and it’s been quiet for nearly a week.
Perhaps the combination of new shaft surfaces and tweaked bearings will run for a few more years. I still have the “new” replacement fan in a box…