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Old 22nd Jul 2017, 10:21 am   #1
BulgingCap
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Default Small desk fan motor vibration

My friend is renovating a vintage desk fan (not sure how vintage as I haven't seen it yet.)
He called me to ask my opinion on the motor which is a small squirrel-cage type with self-centering sintered bearings. It makes a noise when running and vibrates, even if the fan blades are removed. The shaft is not bent, but he says that the end float is about 10mm, which seems a lot.
I suppose that it can only be mechanical balance, and maybe has always been like this.
Any ideas before I call in to pass my judgement?
Regards, BC
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Old 22nd Jul 2017, 10:37 am   #2
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Default Re: Small desk fan motor vibration

Hi BC, You say shaft not bent, to rule this out has your friend tested on parallel, level, knife edge's?


John.
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Old 22nd Jul 2017, 11:14 am   #3
Skywave
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Arrow Re: Small desk fan motor vibration

Occasionally I get that problem with a small 3-blade fan bearing the name GET. Periodically cleaning the entire fan (mainly dust removal) and lubricating all moving metal parts with light machine oil & ensuring all securing screws are tight solves the problem.

Al.
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Old 22nd Jul 2017, 11:28 am   #4
mike_newcomb
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Default Re: Small desk fan motor vibration

Hi BC, the end float seems excessive.

Generally such motors there is a slightly bent, thin spring washer, that stops this but allows for slight expansion. Wonder if it has been lost during dismantling.
Sometimes a paxoline type Washer is used instead of or in addition to.

Can any side movement be felt?
If so, could mean Bearing wear and would explain vibration.

Regards - Mike
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Old 22nd Jul 2017, 11:37 am   #5
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Default Re: Small desk fan motor vibration

10mm is a lot of end float. I wonder if it's been reassembled incorrectly?
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Old 22nd Jul 2017, 3:26 pm   #6
BulgingCap
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Default Re: Small desk fan motor vibration

Thanks everyone-
My friend is an accomplished mechanical bod, but turns to me when confronted with electrical or electronic issues. He reports that the armature shaft seems true but he is going to put it on his lathe with a DTI to check. He has checked, on my advice, that it is not the laminations or windings that are 'rattling', and there is no play in the bearings (apart from the end-float.) The noise is still present with the fan removed. I am to visit tomorrow so will report back. He is a bit of a perfectionist (not a fault...) so it may be a mild noise! I suspect that it was not dynamically balanced from new.
Incidentally- I recently had a Dremel-clone universal motor that had been balanced by dobbing green epoxy blobs on the windings, one at either end. One of these had flown off (it turned at a fearsome RPM when flat-out) and the resultant vibration was very bad.
BC
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Old 22nd Jul 2017, 5:09 pm   #7
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Default Re: Small desk fan motor vibration

Ive had drumming caused by excessive end-float with fan motors when they're very worn. I've never worked out why, unless its missing felt washers that are sometimes used to keep the bearings 'moist'. I cured the last one with a pair of very light springs which overcame the float but enabled the rotor to self-centre.
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Old 23rd Jul 2017, 10:54 am   #8
BulgingCap
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Default Re: Small desk fan motor vibration

Hi Kevin,
I had a look and listen at the motor today. I was surprised that the motor pulled forwards and took up the end float with the fan attached- I had assumed that it would push backwards with the fan reaction. The motor without the fan blades makes a growly-rattling noise that is quite loud. We tried to push the armature each way with a stick which lessened the noise but it was still there. On removal of power the armature still made a bit of noise as it slowed to stop. The shaft is true, and there is a tiny amount of play in the oilite bearings. He has decided to live with it as the unit will be purely decorative. He has other units restored to a high standard.
For info- it is branded as 'Eskimo', made in Australia by 'Jeffries Pty' (I didn't read this myself so spelling?). A nice unit with sculpted cast iron base. No idea of the date but it has a cotton-covered rubber insulated lead with an old Aus plug.
BC
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