The Enermax UC-12EB 120mm 1000RPM "Enlobal" fan:
I used the two-thumb procedure in the Phoronix review to remove the fan assembly:
The ring magnet dimensions are 2.5mm thick by 12mm high.
This last photo is where it gets interesting. The "D" shows a foriegn object on the ring magnet. This proved removable. There's a gouge above "G". And the two "X"s call your attention to a neck in the center post, about 75% of the way down from the top. This neck obviously fits into the collet-like object in the center of the previous photo.
When I put the fan back together, I thought for a moment that the vibration had dropped a lot, but I was wrong. I spent an hour messing with the fan, trying different positions, flexing the fan case, even introducing an external magnet (which did
influence the fan's rotation).
But mostly the story was the vibration, and the vibration coming and going. Setting the fan down on the table top was guaranteed to set off very audible vibrations as the fan apparently almost bounced up and down on the table!
Worse: as the vibration mode changed, the RPM changed! The worse the vibration, the slower the RPM. This sort of makes sense, the more vibration the more friction.
And compounding my frustration was the fact that the fan performed very well during the brief periods without vibration, only slightly louder than a Yate Loon at the same RPM.
I finally came to the conclusion that the fan was permanently unusable and hence suitable for some possibly destructive experimenting. For my first experiment, I decided to use 3in1 oil on that neck on the center spindle. I meant to only use a drop, but I guess it was a large drop - the oil flowed completely around the neck and down into the bottom. I turned the fan assembly upside down, hoping the excess would flow back onto the spindle. With nothing to lose, I refitted the fan assembly and tested the fan again.
The vibration was gone! Set the fan on the table, no vibration! The fan was now reliably quiet and constant-RPM... and still only a little noisier than the Yate Loon at the same RPM.
I think I'll give this a try as an exhaust fan, and see how long it takes for the oil treatment to wear off and the vibration to return. I had turned off the test setup while I typed this up, and when I turned it back on just now the vibration was still gone.
If you're a fan of fans, I recommend you give this fan a try. You should get $11 worth of entertainment from messing with it, and you might learn something that will benefit the SPCR community.