Does my lathe motor need bearings replaced?

[ErichKeane]

I have a big old lathe with a 15HP 3 phase 3450 RPM Baldor motor. It weighs ~300 lbs, so I'm in no hurry to try to get it out of the foot of my lathe or moved around at all

It seems to work 'fine'. It isn't particularly noisy or anything. When starting up, there is a brief 'rattling' sound (that could potentially be something else on the lathe?) at about 30-40 hz, but it goes away at 60 hz.

However, when i went to do some stuff to it, I discovered that the shaft doesn't seem 'attached'. I smacked it with a mallet, and it moves ~1/2" inward, then comes back. It seems to only be held in place by the magnets itself, as it does the little 'shimmy' back and forth until its in the right place. In my head, this means it needed bearings a few decades ago (as in, the bearings are just so bad they basically don't exist).

However, I'm hopeful that this is just the design of some motors? Is it possible that it is a bearingless motor?

 

[JimDawson]

That motor does have bearings in it. I'm not sure why there is that much end play, maybe the bearings are a bit loose in the housing, but I wouldn't concider that to be serious. If the bearings were really bad or gone, the motor would be making a lot of noise when the armature was rubbing on the field segments.

Also not sure why it reacts that way when you smack it with a mallet, it may be spring loaded on both ends. There are no magnets in that motor unless it's a DC motor.

 

[ErichKeane]

Hmm... interesting. Thanks for the feedback! I definitely don't have any obvious rubbing or play up/down, but I was putting a pulley on it and was fighting against it running away as I was smacking at it. I've never heard of a spring loaded shaft before!

It seems to work and is reasonably quiet (at least as far as I can tell...) so I'm less concerned, but looking at the replacement costs for something like this is pretty frightening!

 

[JimDawson]

I put new bearings in my 15 HP Baldor, I think it was about $25 for the two bearings. It took about 30 minutes to change them out with the motor on the bench. As I recall there is a wave spring in each end bell, I can't find a good exploded view of that motor.

 

[ErichKeane]

I put new bearings in my 15 HP Baldor, I think it was about $25 for the two bearings. It took about 30 minutes to change them out with the motor on the bench. As I recall there is a wave spring in each end bell, I can't find a good exploded view of that motor.

I wasn't afraid of the bearing cost, more afraid of the motor replacement cost (if I ignore this and it was bad). Taking the motor out of the lathe ends up being an event (I cannot get a hoist in there), and I'd likely need a hoist to move it anywhere in my shop. The more I think about it, the more I think that replacing the bearings needs to be near the top of my TODO list though.

 

[JimDawson]

New bearings cant hurt. You might pull the belts off and turn it on and see of the noise goes away. It could be the belts slapping around a bit or something in the lathe. If you turn the motor by hand and the bearings sound OK, then they probably are.

 

[ErichKeane]

New bearings cant hurt. You might pull the belts off and turn it on and see of the noise goes away. It could be the belts slapping around a bit or something in the lathe. If you turn the motor by hand and the bearings sound OK, then they probably are.

Its a chain, and the rattle happens without the chain installed. I'm unsure if it is the motor though, there is enough metal things around that it could just be hitting the resonant frequency of SOMETHING else, but I don't know. There is a thick layer of grease/dirt over the motor/surroundings, so it could be a lose washer or something and I'd have no idea.

The motor turns fine by hand, and I didn't notice anything bad sounding but perhaps I'll try again. I might just suck it up and see what it'll take to get it out of there to replace the bearings for peace of mind. That, and to harvest that 1/4" thick layer of dirt

 

[Ulma Doctor]

I hope i'm not too late for the party here...

it is common for motors to have thin wavy washers at one end
the wavy washer gives a little when the motor is starting.
after the spring pressure overcomes the initial longitudinal movement, the motor shaft returns to the path of least (mechanical)resistance

i would not usually expect to see 1/2" of end play movement, especially in a 3450rpm motor

i have experienced motors that have thrown the inner dust shields from the bearings and making one heck of a noise
you may(or may not) have a similar situation

simply mark both ends of the motor end caps relative to the field housing, so as to assure proper re-assembly
pop the pulley off the business end
remove the bolts running through the motor
knock the end caps off with gentle persuasion
the bearings will then be exposed
a 2 jaw or 3 jaw puller can then be used to remove the bearings
if you take a look at the namplate, (baldor often used to put the bearing numbers on the nameplate)
otherwise look for identification numbers,( ie.6207- 6307 were common bearings used for that hp range of motors)
otherwise extract the bearings and measure ID, OD and Thickness in millimeters and you can find the bearings through reverse osmosis

at this stage inspect the wavy washer, look for cracks or broken pieces

re-assemble in reverse order!

 

[ErichKeane]

I hope i'm not too late for the party here...

it is common for motors to have thin wavy washers at one end
the wavy washer gives a little when the motor is starting.
after the spring pressure overcomes the initial longitudinal movement, the motor shaft returns to the path of least (mechanical)resistance

i would not usually expect to see 1/2" of end play movement, especially in a 3450rpm motor

i have experienced motors that have thrown the inner dust shields from the bearings and making one heck of a noise
you may(or may not) have a similar situation

simply mark both ends of the motor end caps relative to the field housing, so as to assure proper re-assembly
pop the pulley off the business end
remove the bolts running through the motor
knock the end caps off with gentle persuasion
the bearings will then be exposed
a 2 jaw or 3 jaw puller can then be used to remove the bearings
if you take a look at the namplate, (baldor often used to put the bearing numbers on the nameplate)
otherwise look for identification numbers,( ie.6207- 6307 were common bearings used for that hp range of motors)
otherwise extract the bearings and measure ID, OD and Thickness in millimeters and you can find the bearings through reverse osmosis

at this stage inspect the wavy washer, look for cracks or broken pieces

re-assemble in reverse order!

Not too late it was late when I got home from work, so I didn't get a chance to try and pull it out. At 300 lbs, removal is likely to be an adventure !

 

[C-Bag]

Years ago I bought a mechanic stethoscope and it's amazing what you can tell about bearings with it. Lots of times I could hear a rough bearing long before it got bad enough to feel play. It was the only way to hear all the different bearings in the accessories on a running engine not to mention lifter and tappet noise etc. it was also great for listening to bearings on electric motors and gear reduction boxes.