Electric motor shafts

In an effort to educate myself and hopefully gain a 3/4" shaft in the
process I attacked an electric motor I bought for $1 in a garage sale. It
has seen better days. I suspect it powered some sort of woodworking machine
as the whole thing was coated liberally with sawdust inside and out. The
insulation was rotten and falling off the wires. I should mention that
physically it was a big beast but only 1/2hp (the label was barely
readable).
I managed to get the front off. I expected ball bearings supporting the
shaft but there were sleeve bearings at both ends - the front one quite
chewed up which surprised me as the shaft seemed to turn freely. The oiling
port was plugged with sawdust.
I got the fan off and tried to get the rotor off but could not even shift
it. I should say I have never attempted anything similar and use of Workmate
and sledge hammer is probably not the recommended method. I managed to
mushroom the end of the shaft nicely but the rotor would not shift.
The rotor sits on the central part of the shaft which is 1.25" as opposed to
the ends which are 0.75". There appears to be a small key in a slot but
trying to punch it out did not meet with success either.
Questions:
1) Are sleeve bearings usual in electric motors or is this some old, cheap
model?
2) Are shafts in such motor usually machined in one piece or is a 3/4" shaft
rammed into a mandrel to hold the rotor? In spite copious cleaning I cannot
tell for sure.
3) I am puzzled at the inability to shift the rotor. If the sledge hammer
did not do the job is a gear puller (or some other gizmo) likely to succeed
(as well as protect the shaft, of course)?
4) Am I missing some method by which the rotor is held onto the shaft
rendering the sledge hammer ineffective?
Books and Google have been no help. Neither was liberal application of
Liquid Wrench.
Thanks,
Reply to
Michael Koblic
Loading thread data ...
Can you get your $1 back?
Reply to
Buerste
1) properly lubed sleeve bearing have a longer service life in certain applications like furnace blowers. In the 'old' days, they were used in the majority of motors since ball bearings had both shorter life and were much more expensive.
2) Rotors have a steel shaft pressed through a stack of laminations made from a high silcon steel. The stuff is extremely hard and brittle. Easily bites into a normal steel shaft.
3) If you try pressing the shaft the way it was pressed on, you MIGHT have a chance. Smashing it with a hammer won't do the job. Gear puller is not even an option.
Michael Koblic wrote:
Reply to
RoyJ
What about modern balll bearings? i
Reply to
Ignoramus20387
No, and I would not want to. The motor came with two pulleys attached, one of them 3-step. As the new ones would cost me about $25 I consider myself $24 ahead not including the 3 hours of amusement I have had so far with the motor :-)
Reply to
Michael Koblic
We have a WINNER!
The rotor was seriously pressed on that shaft, you probably won't get it off. Bronze bearings have a lot of good points. If kept lubed they last a very long time.
Reply to
Buerste
I want some of those modern balll bearings, I only can get old fashioned ball bearings...lucky bastard!
Reply to
Buerste
The Workmate doesn't have enough inertia to restrain the armature. You need to back it with a hunk of iron at least as heavy as the sledge hammer. A long piece of heavy pipe might work if your collection of scrap metal is inadequate.
Think of the toy with a line of suspended balls, hit one end and only the far one swings out. Or bucking a rivet.
Jim Wilkins
Reply to
Jim Wilkins
I think that a more effective way to remove the shaft would be making a saw cut into the rotor toward and inline with the shaft centerline. I haven't tried this, but I wouldn't think that it would be necessary to make more than one cut to release the contact pressure between the rotor and shaft.
Silicon steel used for motor and tranformer laminations, that I'm familiar with has been very soft steel, and not at all diffiult to cut. The difference of an induction motor rotor is that there are the steel laminations surrounded by a cast aluminum alloy (which is what makes up the windings, or current paths, similar to a copper wound armature). I believe the aluminum alloy would prohibit the use of an abrasive disk to cut thru the rotor material.
I don't think that trying to drive a shaft out with a hammer will produce much effect on the position of the rotor.
Polished sleeve bearings are very practical for numerous applications (provided that they are lubricated properly). There might be an very noticeable opening in the sleeve, referred to sometimes as the window, and many motor housings will have an arrow or other indication of where the window is located so the installer can apply the side load to a location where the window is opposite the load side. The oil wick material might contact the shaft thru the window for continuous lubrication.
On some older domestic USA motors, the manufacturer may have used cast end end bells for the motor end plates that are very similar for both sleeve and ball bearing models. For the ball bearing models, they eliminate the extra material used for the sleeve model, and machine a counterbore/pocket for the ball bearing assembly. This means that if a HSM discovers a good motor with worn sleeve bearings, he can sometimes machine away the sleeve support webs in the end bell castings to install ball bearings. I've done this just to see if it could be done, and the results were as good as if the motor originally had ball bearings.
This modification wasn't difficult to perform on a 9" lathe with 4-jaw chuck, and the the cost of the bearings was only a few dollars.
Reply to
Wild_Bill
Current ball bearings are made to better tolerances than older ones. The ABEC numbers (higher is better) have stayed the same but a 30 year old ABEC-3 is pretty close to a current ABEC-1. And even the import specials are pretty good.
Ball bearings are good for higher speed and lower friction. Sleeve bearings are good for lower speeds, higher average loads, but have slightly higher friction (means heat in the bearing). A sleeve bearing actually floats on a film of oil (assuming it's properly lubed) so there is no metal to metal contact. Ball bearing have metal to metal contact because the balls squeeze the lube out of the point of contact. Everything is hardened but there is still the wear factor.
Sleeve bearings take severe impact loadings better. The relevant surface area of a 3/4" shaft is around 1/2" wide. Compare that to the 3 or 4 ball point contacts in a ball bearing. Of course a roller bearing has much more contact area, they are used for the high impact applications.
I have some bearing balls out of a race car CV joint that show nasty cratering under a 10x magnification. You can see rows of chips taken out of the hardened surface, look almost like the gouge marks from a backhoe tooth on a concrete road surface.
Ignoramus20387 wrote:
Reply to
RoyJ
Thanks, I'll watch for that.
Reply to
Jim Wilkins
Sleeve bearings are common in older motors. Like Roy said, a sleeve bearing has some advantages over a rolling element bearing. They take high loads better. They are also quieter as their stiffness doesn't vary with position. Quite often sleeve bearings are more expensive than rolling element bearings.
Probably there is a shaft of 3/4" diameter (which is of a slightly larger diameter in the centre; you are unlikely to be able to remove this without turning down the shaft) which is somehow attached to the rotor. The three methods I've seen for attachment are: (i) small splines on the shaft (the shaft is then pressed through an undersize hole in the laminations), (ii) a key and keyway, and (iii) welding. Depending on the method of attachment, you may be able to remove the rotor, but it probably won't be easy. The rotor has to stay firmly and reliably attached to the shaft in service.
Unless you have a very strong gear puller, probably not. A good strong puller, like some of the larger Gedore/Baldur models, might be able to move it. But a cheap gear puller won't.
It sounds like your rotor is secured by a key. If it's a taper key, this is probably why you can't remove the rotor. Taper keys are designed to jam tight. If it's a parallel key, there may be a threaded hole for a grubscrew which holds the key in place. If so, you need to remove the grubscrew. Rust may also be jamming the rotor in place.
If it's a taper key, I find the best way to remove them is using a strong gear puller. You need a puller capable of exerting several tons of force. Also, if you have to pull the rotor in the direction which tends to push the taper key further in, put a piece of metal under the head of the taper key to stop it sliding further in and jamming the rotor on tighter.
Good luck!
Best wishes,
Chris
Reply to
Christopher Tidy
Actually no; when the design is right there is still a very thin oil film there (although it is vulnerable to dirt in the lube). Google EHL
No again, the cratering will be pits produced by fatigue cracking, caused by stress cycles. But as you say, the stress levels are very high
Reply to
Newshound
Roy, if you want to sell one of those balls with the pitting, drop me a line (chris AT ruggedmachines DOT com). I'm looking for an example of a spalled surface that I can photograph under a microscope.
Best wishes,
Chris
Reply to
Christopher Tidy
Sent private response.
Christ>
Reply to
RoyJ
Thanks, Roy. It hasn't arrived in my inbox yet, but I'm sure it'll be there tomorrow (unless you sent it to the address in the message header, which is spam-trapped because of the insane amount of spam I was getting?). I'll get back to you on it tomorrow.
Many thanks,
Chris
Reply to
Christopher Tidy
Thanks, everyone! I have learned more reading this thread than in three days of searching and googling.
I think the end result with this item is scrap yard: the 3/4" section of the shaft is too short for the coutershaft I had in mind. I could cut into the rotor, remove it that way and then turn the rest of the shaft down to 3/4" but for that ...I would need a lathe! I am sure the said scrap yard will provide the necessary 3/4" shaft in some form :-)
The positive outcome of this may be that I shall feel more comfortable designing the counterhaft with cheap sleeve bearings rather than expensive pillow blocks.
Thanks again,
Reply to
Michael Koblic
The only real advantage of ball-bearing pillow blocks is that they can swivel to align with the shaft, although as you've noticed some swivel more freely than others. Sleeve bearings can be very hard to align if you can't drill and ream them in one setup.
Reply to
Jim Wilkins
Copper water pipe out of the question then ? Worked before...I guess for 3/4" I should use something more sophisticated. I was thinking a couple of bronze flanged bearings for $2 each in home-made pillow blocks. Not a good idea?
Reply to
Michael Koblic
All depends on what you want to accomplish. The eccentrics on my compost sifter run in fairly loose, well greased oak. Gerry :-)} London, Canada
Reply to
Gerald Miller

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