HELP!: Thunk, thunk, thunk....

Huh.
Mounted my sanding disc to my table saw yesterday to ease the edges of some 1/4" thick mounting brackets for a new top for my mobile workbench. Started up the saw, everything sounded/seemed fine.
Put my ear protection in. Started to grind a coupla pieces. Weird noise, but I thought that the sanding disc at work was the cause. Finished easing the edges and pulled my ear protection outta my ears. THUNK THUNK THUNK (at 3400 bpm)!
Frick. Something stuck in the saw? Open the cabinet. Nothing. Fire up the saw again. THUNK THUNK THUNK. Weird. Huh. Take the belt off. Spin the arbor. Smoooooth. Spin the motor. Smoooth....
Remove belt, try to move pulleys on arbors. Nope. Not by hand.
Put the belt back on. Slowly spin the motor. Thunk. Thunk. Thunk. Take belt off. Noise gone again. Put belt back on. Thunk. Spin motor backwards. *Very* light thunk. Check alignment of belt ribs with pulleys. Adjust so there is 'misalignment' of belt (shift ribs over 1 slot on one pulley). Thunk disappears briefly, comes back.
Observe both pulleys relative to thunk timing. Hmmm... perfectly synced with the motor. Damn. Frick. Thing is like maybe a year old. Well, got a five year warranty. Thank god for that.
So, I have very little desire to remove the motor from this puppy - three horse's gotta weigh like 150 pounds.... Gonna be a giant PITA for sure. Maybe it's fixable without removing the motor?
Anyone have a suggestion that isn't gonna make me cry?
TIA
D'ohBoy
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Before you dismount the motor, take a real close look at the belt(s). If there is a crack, or an internal cord problem, it might make noise. Couple of thoughts:
1. Mark a spot, on the belt, with magic marker, drop of paint, etc. Watch the spot as it passes over the pulleys to see if the thunk occurs as it goes around a pulley 2. Even before 1, lightly (and carefully) touch a bar of soap to the belt surfaces that contact the pulleys. Belt dressing is better but soap works. If it is a belt problem the noise will probably stop or change instantly.
If these work, you might need a belt. If not, start thinking bushings or bearings in the motor or arbor.
simple and worth a try. RonB
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D'ohBoy wrote:

I'm sure that you've done this, but since you don't say so explicitly I think it worth mentioning--have you carefully inspected the belt?
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Actually, no. I looked at it briefly, but nothing really jumped at me....
And there was a post (here or there or someone) a while back from someone reviewing or talking about their steel city ribbed single belt and putting it on wrong originally and messing it (the belt) up....
I have a hard time believing that it could turn so smoothly and thunk- free by hand *without the belt* but be so messed up *with it* if the bearings were bad.
Gonna poke at it some more... updates as things change. I'm betting I hosed that belt by installing it wrong initially. Or the belt was defective.
Thanks to all! Man, if it ain't my jointer (see my earlier whiny posts about a twisted fence), it's my table saw, or my bandsaw.
With the bandsaw, I had to mill the lower bearing assembly in order to pull the bearings back far enough to accommodate a 1/8" blade (within the specs for the saw) but at least I figured that one out on my own. Thanks, Rikon!
My brothers and I have a saying (apropos to Mother's Day): If it's not one thing, it's your mother ;)
D'ohBoy
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D'ohBoy wrote:

I think it's belt related for sure. Bushings and bearings spinning around 3400 rpm don't go thunk, thunk, thunk, more like screeeech.
The only thing going around slow enough to go thunk, thunk, thunk is the belt? That's my take.

Yes, something like that... have you found the problem yet?

I remember that post, don't remember seeing the actual fix. My guess on that was technique until you said it happened on edge jointing rather than face jointing...

I like that one, already stuck it in my quotes file...
--
Jack
GO PENNS!
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Hi, Jack -
I actually did solve this one - and posted the issue. But for you, as you missed it, it was the set screw in the pulley mounted to the motor shaft. Bout 3/4 turn loose. Surprisingly loud thunk for what it was.
As for the jointer, I have not had the time to solve that one. But I will attack it at some point...
You're welcome for the quote. That's shareware, free to use but no distribution without a license....
;)
D'ohBoy
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Sounds like the bearing are shot.
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If the clunk is there when turning by hand, I seriously doubt that the belts would make any noise if they were bad.
Something else to consider and this has happened to me in the past, If the set screw/key loosen you can hear a clunking sound as the pulley wiggles under the pressure of an up to speed motor. I'd check to make sure the set screw is tight.
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On Sun, 10 May 2009 10:00:41 -0500, "Leon"

Also check the fan, I've had it rub against the fan cover.
-Kevin
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DING DING DING! We have a winner! Leon was right. Thanks! The set screw in the pulley attached to the motor was loose. Weird that such a tiny screw could make any difference at all - or would be considered sufficient to the task, given the forces on that piece.
Okay, so now that I have identified/repaired the source of issues, is there any possible complications due to that set screw having been loose? There was also a wedge driven into a keyway that locked the pulley in place.
Anyhoo... thanks again, Leon.
D'ohBoy
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"D'ohBoy" wrote
DING DING DING! We have a winner! Leon was right. Thanks! The set screw in the pulley attached to the motor was loose.
Don't tell anybody, but Leon is psychic. That is how he figured it out.
He "saw" the problem. <G>
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D'ohBoy wrote:

Make sure that the pulleys are aligned properly. It could have wiggled a bit when the set screw came loose. Misaligned pulleys can cause some distress for the bearings. Also consider a bit of Loctite or similar thread goop to keep it in place. My Griz jointer had a this same problem.     mahalo,     jo4hn
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<snip>

Thought I'd add this.. I haven't had Loctite around for years, since I gave up wrenching, but as a turner I DO have flexible CA.. Seems to work as well, so far, though I'm not sure if it will last as long.. YMWV
mac
Please remove splinters before emailing
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DING DING DING! We have a winner! Leon was right. Thanks! The set screw in the pulley attached to the motor was loose. Weird that such a tiny screw could make any difference at all - or would be considered sufficient to the task, given the forces on that piece.
Okay, so now that I have identified/repaired the source of issues, is there any possible complications due to that set screw having been loose? There was also a wedge driven into a keyway that locked the pulley in place.
Anyhoo... thanks again, Leon.
D'ohBoy
Consider replacing the set screw with one that has a fresh end. Also you might consider adding a drop of LocTite, the one that will allow you to loosen at a future time.
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