vibration at shut off???

After turning off my bandsaw and it is slowing down, a point is reached when I hear a clicking sound at the motor. Immediately the motor shudders and sets up a noisy vibration, like it is a brake or something. It lasts for about two seconds. The motor is a 1 1/2hp leeson 230v cont duty. I have no idea what causes it or how to fix it. Help will be appreciated.

Reply to
Doug Olsen
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Seems like the armature is becoming excentric (out of balance). The noise could also be a problem with a centrifugal switch.

Dave M.

Reply to
Dave M.

On Sat, 29 Nov 2003 03:48:26 GMT, "Dave M." Gave us:

One side closes before the other does, hence the momentary imbalance.

Use some dry silicone lube spray on it.

Reply to
DarkMatter

If it is an induction motor with a switch or even a starting relay, then the MOST likely cause of problems is a bearing failure cause by lack of lubrication or use of a oil which messes up the passage of lube through the sleeve bearings.

Abearing failure often lets the motor start (and, sometimes, come up to speed) but then the oil film fails and the rotor and the stator come into contact and the motor slows down.

The cure? MAYBE you can find a matching end cap (worked for me once) but most likely you will replace the motor.

I don't know a motor problem that silicone would "cure."

Reply to
John Gilmer

That's what it sounds like to me too, John. The motor shaft goes into asynchronous whirl mode(i.e. the motor shaft starts to walk around the now-oversized bushing bore instead of just spinning concentrically in it) as it passes through some critical angular velocity for the given load condition. The motor accelerates very quickly upon start-up so it has no chance to go into asynchronous whirl; as it slows down, it has plenty of time to do it. Once it starts, it won't stop until the rotor stops turning. What an awful noise that can make!

Reply to
Nukie Poo

On Sat, 29 Nov 2003 04:54:10 -0500, "John Gilmer" Gave us:

Well, are you sure that 1 1/2 HP 230 volt AC motors have mere sleeve bearings? Also, if you read the original post, you'll find that he describes a clicking sound. That sounds like a centrifugally operated switch to me. If one side stays flapped open and the other side closes, an imbalance occurs that has the exact parameters he describes. The mechanism is supposed to open and close symmetrically, and the design should only allow that, but it could have a failure mode introduced into it. A missing spring or something.

Reply to
DarkMatter

message

Vibration time (speed at which vibration starts) could be coincidental with the time when the switch closes ?!?!?! Art.

Reply to
art

I agree with Dave here, it sounds like a dynamic balance problem. Sometimes balance problems only exihibit themselves at a certain RPM's. Maybe an old bearing?...Not sure of the age of this saw...Have you tried a second blade...maybe the blade is the problem...Hope that helps....good luck with the saw...Ross

Reply to
Ross Mac

the problem described by the OP imbalance after hearing centrifugal switch contacts caused by one pendulum sticking

Reply to
Someone

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