Jet 1642 Motor gone bad

[Brad Adams]

Under normal use it probably wouldn't have bent. You said it yourself, the noise started last fall. Running a motor with bearings going out, which was probably the noise you heard, never ends well. I see it all the time on motors. I'm sorry it went bad, but blaming the manufacturer is wrong on a six year old lathe.

[Jim Underwood]

Right. So "bad bearings" cause a bent shaft? I don't think so. It's the other way around.
The shaft was bent and that's what caused the bearings to "fail". In fact, I don't think there's anything wrong with the bearings and I've maintained that all along. They are smooth as silk...
I've seen the machining on this motor and described it to you. I've seen Jets "quality" on my original 1014 like a pulley that wasn't concentric with the hole. Jet's machining is sub par. This motor has had NOTHING done to it that should cause its failure. It should last more than six years....

[Dwight Rutherford]

I'm with Brad on this. Question, if you heard a strange noise in your car, would you just ignore it and continue to drive it until it died and then blame the manufacturer?

[Jim Underwood]

As if the shaft wouldn't be bent if I hadn't kept running it?
Nah.
Either the shaft was bent from the factory and finally showed up six years later, or it was defective because the steel was too soft or there was a void, crack or something else in it.
An electric motor isn't like a car engine where if you run it without oil you'll ruin it. Or brakes where if you continue keep driving after it makes metal on metal noise you'll be buying rotors as well as brake pads.
If the motor began making a barely noticeable noise, and then slowly got worse, then the problem was in the shaft to begin with. It's not like stopping was going to prevent anything, Especially if it wasn't bearings.
And it's NOT the bearings. I've replaced enough bearings over the past thirty years to know what bad bearings look and feel like.
I mean think about it. There's only like three moving parts in this motor. Two bearings and an essentially one piece armature consisting of the shaft and rotor. There's no brushes, no commutator bars. Then there's the stationary case and it's stationary coil lamination assembly.
That's it. Very simple.
Now if begins making noise what possibly has gone wrong? Bearings. Those have been eliminated. The case coil assembly could have come loose. That's been eliminated. The rotor could have been coming apart. That's been eliminated. Or. The shaft could be bent. That's what it is.

Now there's only two or three possible scenarios that could explain how the shaft came to be bent.
One, it was bent from the factory and slowly got worse over the years.
Two, the shaft wasn't bent, but something I did caused it to bend.
Three, the shaft had a defect (either machined in, inherently from a void or crack, or from substandard materials) and bent from normal use.

Obviously I lean towards a combination of reasons one and three. You could say I suppose that normal use caused the problem, but I maintain that a motor should NOT exhibit problems from a bent shaft from normal use unless problems one and three were present.

Now at least two people condemn me for continuing to run the thing after it started making noise. Here's the deal though. First thing I did was check the part list. There are no parts available for the motor. The only thing you can actually replace are the bearings.- from an aftermarket source. And when roller bearings go bad they don't go; "knock, knock, knock", they go "growl". (Unless it's a preload problem and then it's not technically bad bearings. And in this case it's a moot point because there AIN'T no preload.) So it's not like lack of use prevented the shaft from bending or made it so it could be fixed. No. By that point the damage was already done. You can't replace the shaft from parts available from Jet, and no motor shop will fix anything this small- because it's just not cost effective.
And it was already out of warranty.

So what am I supposed to do? Stop using it? Why? The only "fix" is to replace the motor.
So I chose to get as much use out of it as I could knowing the pulley shaft was wobbling. The ONLY thing you could fault me for is not calling Jet immediately.

I still maintain that the shaft should not bend under normal use, and certainly not from very occasional use..

[charlie knighton]

I still maintain that the shaft should not bend under normal use, and certainly not from very occasional use

I agree.....not sure how would one go about bending a shaft......only thing I can think of is to lock shaft and beat it with sledge hammer, somehow I cannot see a turner doing that.

[Roger Chandler]

It sounds likely to me that the metal in the shaft was not treated to harden as well as it should have been [defective] and heat inside the motor has warped it..........that would explain why you have it manifesting after 5 years of use..........just my 2 cents!

[Jim Underwood]

Whenever I resolve this, I'm probably going to cut the armature apart and inspect the whole shaft.
I don't think it was hardened.
Something happened to the middle of the shaft....

[Dan Hintz]

A hardness test along the length of the shaft wouldn't be hard to do... though it might not take into account case hardening.

[Jim Underwood]

Here's a quote from another forum which explains what I think really happened:

"From a mechanical engineer’s perspective – I’d guess the shaft has been bent since the beginning and it’s just taken this much time to get worse because of the light use. Your jump rope analogy is pretty good. If it was bent even just a little bit to begin with, then the center of mass is going to be off from the center of rotation and will get pulled out due to the centripetal force. Think merry-go-round and sitting right in the center vs. sitting a little off center and getting pulled to the outside. That force gets higher as the RPMs increase so at those really high speeds it’s applying more force out away from the center making the metal bend more than what you can generate by hand. Add to that Force + Time = Fatigue so as the metal fatigues it becomes easier to bend. As the fatigue gets worse, the metal bends more and the center of mass moves further away from the center of rotation which makes the force higher which makes the fatigue worse which… You get the picture, right? Sounds to me like you’ve just recently accumulated enough time that the metal of the shaft has fatigued enough and the force at high RPM is warping the shaft enough that the armature is finally hitting the surrounding coil."

[Jim Underwood]

Looks like the motor shop is too busy to help. They're saying the motor has a special mounting that they can't duplicate. I can't really blame them for not wanting to fool with my mickey mouse motor when they're in the middle of a rush job on a 600 HP motor rewind...

[Jim Underwood]

MMMMmmmmmmmm….. that Crow sure tastes good. A bit chewy though…
Just dropped the motor off at the motor shop. They were kind enough to give me 15 minutes or so. Took the end caps off and inspected. Asked what was the reason I took it apart in the first place – bearings gone bad?
I said, no, the armature was hitting the coil laminations, and I replaced the bearings just in case that was the problem. But it didn’t fix it, because, I said, the shaft is bent.
He says, well sometimes the belt gets tightened too tight, and then the bearings act as a fulcrum and the tension pulls the pulley end away from the bearing, and the center of the shaft bends away from that tension. He says, I can just about tell you which direction the tension is being pulled from where the armature is hitting the coil laminations. And when we pulled it back apart, sure enough, the armature was hitting just about the predicted spot.
The upshot is that he took pity on me and was going to bend the shaft back to true, and trim a bit off with the lathe to make sure it didn’t hit anymore – for less than $100.
And the replacement motor option is kinda dead in the water. The motor mounting was different, a C-face needs a recess to mount in, plus the bolt pattern was different and the clincher was the 5/8” shaft being smaller than a 16mm shaft…
I trust these folks. I’ve been dealing with them for years and years, and they’ve ALWAYS treated me right even when it would have been easy to take advantage. And they do a LOT of business with some REALLY big industry folks here. (They’ve got a couple of 700 HP motor jobs after they finish the 600 HP job, right this minute.)
So, I’ll take their word for it, apparently I did cause the problem. I admit, I was too quick to blame Jet for it.
Mmmmmmm….. Crow. Jest eat it….

[Dave Cullen]

I've never seen a bent motor shaft unless it was whacked by something. Seems like either a design flaw or manufacturing defect to me. I don't think Jet is totally blameless here.

That said, is the bottom line here that the belt was over tightened? Did you put the Fear-Of-God into tightening it? Even if so, I can't imagine a motor failing before the belt.

Anyway, I'm really glad you have a reasonable solution at hand. Is there a corrective action plan (like go easy on the belt)?

[charlie knighton]

thanks for sharing Jim, it was a revalation

[Dan Hintz]

Thanks for the update, Jim, even if it means tonight's dinner is a little less palatable.

[david privett]

Back in the day before serpentine belts and automatic tensioners, I remember hearing that over tightening v belts would cause bearing failure mostly in alternators. But never personally seen it. And using belt deflection to judge how tight was somewhat a personal choice. But never heard of causing a bent shaft, but I do not work with motors very much. curious. I your opinion is the pulley out far enough past the bearings that they could have that much leverage advantage? If so are we back to the shaft being under engineered?