Best Fix For A Worn Axle?

Thanks a lot for all the advice and opinions.

With regards to the over heating event, the motor did run perfectly well for quite some time, after I replaced the broken fan, so I doubt whether the was any damage to the windings or casing. I will have it checked out though, because I intend to use this motor as a standby, should any of the other two 70kw's that I'm using, develop a problem and there's no use in having a standby which isn't 100% reliable.
I'm quite confident that I would be able to turn it down and re-sleeve it successfully. After all, it is my own motor, so should I stuff it up, it won't be the end of the world and I can always take it to the machine shop that I regularly use to rescue it. We have a very good relationship, but I can just imagine the comments I'll have to face, should I call on them to bail me out!

My initial though was to weld the axle and then turn it down, but my toolmaker friend warned me that the heat might warp the axle, hence my leaning towards the sleeve, instead.
The metal spray sounds rather interesting and to be honest, I didn't know it existed. I'll look into that as it seems to be likely solution. The build up required on the axle is minute, so maybe this would be the way to go.

Thanks once again. I'll ponder on this some more and then decide what to do. I'll keep you posted.
 
Your friend is quite correct. In my repair days, if a shaft was damaged beyond what the spray would build up, welding was one frequently used option, but required a lot of straightening of any extended area beyond the repaired are, and was generally used more on the stub end of the shaft rather than the output shaft end. I don't believe you've specified which end though, so it might still be worth discussing. On the stub end, there are a few other concerns that need to be addressed.
 
The problem is indeed on the stub end of the shaft , Tony. I'm interested to hear more about the concerns you mentioned?
 
Lood, the main thing is the location of the shoulder the bearing seats against. When you weld up a shaft like that, you should envelope the shoulder as well, which of course means you have to re-cut it. Therefore, you need an accurate measurement between the shoulders from the other end and its shoulder. Welding will build up at the outside corner of the shaft as well, so using a depth mic is sketchy, unless the very end of the shaft is verified square with the axis. Then you can carefully clean up just the face as the first operation and with out removing material from the original face, re-establish the location of the shoulder. It is imperative to maintain the shoulder to shoulder dimension.
Even when you weld such a short area, it may still distort, so the center hole may not be reliable. In a best case, you can run a steady rest just behind the built up area. That area usually isn't running dead true with the bearing areas though, so you have to true it up using the existing center hole prior to any welding. Then you can and should reclaim the center hole, and finish the job without the steady rest. If there simply is no room for a steady rest, careful placement of shim stock in the center hole can get you true again, but you still need a reference surface behind the repaired area to run an indicator, so turn a small indicating band before welding. If you are forced to go that route, frequent checking that it still runs true is necessary. In fact, my preference is to machine just to skim an area for the steady rest and true up the center before proceeding. Don't try to weld it up from the present size. Turn it down say, 1/8" or more so that you won't be finish cutting right in the blended area.
 
There is a good YouTube on a fix like you are talking about. It's one of Doubleboost's videos. He knurls the worn down area and presto, the shaft increases in size to make a nice press fit for the bearing. A stuck bearing was the cause of your shaft wearing down, very likely so a good bearing will work the very best on a knurled shaft.I have also used a prick punch to do a similar thing to shafts in the past and they worked out fine but knurling is the best solution in my opinion.

Pete
 
I can't recommend a knurl repair on a ~100 hp motor. The slight imbalance that is tolerable on a large, heavy rotor like that translates into quite a bit of force would likely soon reform the knurl. I have knurled many smaller motors, but never a larger motor.
 
I agree. I really didn't know from the KW rating of the motor how big it was. I would go with spray welding if I could find someone to do it. Abomb on YouTube does some spray welding.
 
Yeah, I really don't know about the exact area in South Africa he is in, but if there is much industry, spraying would be the easiest if he had to have it done outside his own shop.
 
Back in my college days, I worked at a deep hole drilling shop in Houston. We had a 75 HP DC motor break a shaft. I made a new shaft for the motor, mechanic pressed it in the rotor and re assembled the motor. I guess the motor is still running. That was 38 years ago.
BTW- the old motor was a old used motor that came off of rolling mill equipment out of a steel mill. The motor was retrofitted with flanged bearings on each end of the bell housings. It replaced the old babbitt sleeved bearings that originally came on the motor.
 
hmm, let's see.....Deep Hole, Hole Specialists (not likely, fairly new), Boring Specialties (or Specialists??)......all I can think of atm. Used several down there when I didn't order hollow bar and let the supplier handle the bore work.
 
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