Normally I sleeve shaft bearing fits, as I am not a weldor though I can stick like metals together reasonably strongly, though often ugly.

In addition, normally when a motor shaft comes in with this kind of crash, there is usually enough other damage to make repair not economical.  This one seems to have been caught just in the nick of time where the electrical and other mechanical issues are still repairable.

My experience with trying to turn a welded shaft to a proper bearing fit has been fraught with frustration.  There always seem to be hard and soft spots that machine to different sizes.  The tolerance that I have to hit on this particular bearing size is only 0.0006" on diameter.  Yes that is six ten-thousandths of an inch.  We're splitting hairs here.   (100 mm +.002 / +0.017,  or 3.9371 to 3.9377 inches)

The primary question that I have here, is how to properly prep the shaft, and weld with what method.  Also, if stick welding, what rod should be used, if wire feed, what wire, gas and other settings?  I'll  have one of the other guys who have more welding experience do the job, though they don't seem to have as much technical knowledge about material behavior.

The generator rotor shaft in question:





As you can tell, there is a bit of bearing material friction welded to the shaft.  It is not nearly as bad as some that I've encountered, however.

Have it spray welded.



As for turning it, maybe you could grind it instead.  I've never priced a tool post grinder, but it would be pretty easy to make one with a die grinder.

Here's one idea...

https://www.youtube.com/shorts/WoG9nZQOk6Q

I do have a Dumore pedestal grinder, but that is slow process.  I did warn the sales guy that I may have to go this route and that it would take a substantial amount of time. Plus, it is abrasive for the lathe ways, no matter how much you try to protect them.  Clean up afterward is also adds to the time.

As far as spray welding goes (metalizing), that used to be the go-to method.  However, the local environmental agencies have shut down that process.  No one who has done the work in the past wants to pay for the required fume extractor/scrubbers.

Ah, good points.  I didn't realize that the spraying had been clamped down on.  Some things used to be easier than they are now.  I wonder if it could be brazed.  That would make it easier to turn.  Anyway, good luck!

Well it was welded up today.  After the first welding, I turned it close to size, but had a lot of voids.  After the second touch-up welding, it looks much better.  However, like my experience has shown, there are slightly harder spots, and softer ones which make for as much as 0.002" difference depending on where I measure.  I still have about .015 left, and will grind the remaining.  Unlike some bearing crashes, the hard shell where the bearing friction welded to the shaft was quite shallow and turned down easily.  

Monday, I grind to size.  The, I turn my attention to the bearing sleeve replacement job in the end bracket.  (There are three generators of like size with the same bracket issue---which is rather normal.) Having multiples does save time since the set-ups are essentially the same.

ETA:  Brazing will not hold up to the abuse that these generators receive.   It can work on a less than 10 Hp fan or direct drive motor, but we tend to limit that kind of  shaft repair to 50 Hp and up.   Even then, it usually becomes economically sound on greater than 250 Hp.  Specialty motors are the exceptions, as they seem to be made out of unobtainium, or have extravagant lead times.

Post pics!

I didn't take the time to take photos of the welding before turning, but on Monday, I'll be sure to show the Dumore set-up and the few defects left.

BTW, working in an electric motor shop has some perks in that copper bars (heavy rectangular wire and bus bars) are quite readily available.  I fitted a couple of said wires to fill the slot.  This made for a pretty decent wall on the slot without having to put this medium sized rotor on a normal sized mill.  I've done that kind of thing before, and it gets a bit awkward.