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Remove Large gear from shaft - damaged key

Overland

Stainless
Joined
Nov 19, 2017
Location
Greenville, SC
I've been asked if I can remove this gear from the shaft.
Gear is about 20" dia, 3" wide, shaft about 4" diameter, from a scrap wood grinder. Something dropped into the grinder, stalled it and turned the gear a couple of degrees and damaged the key.
I don't know what the other end of the key looks like.
He wants the key replaced as the grinder has to be reversed to clear jams.
Do you think the shaft could be just pressed out through the gear ?
Maybe some heat on the gear ?
May need to recut the keyways, I guess.
Appreciate any insights.
Bob
 

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Oof! Brute force seems to be the way to go, given the level of damage. You'll need a big press. I doubt heat would help much since the key interference is going to be massive, and you can't expand the gear to expand enough to undo it. If the gear was driven by a single pinion, there's a chance the shaft is bent, too. You might want to check how much it's bent and whether the shaft is repairable before investing a lot of time trying to get the shaft out gracefully as opposed to cutting it out and making a new shaft. How are the gear teeth? They need a close inspection given the state of the key.
 
Oof! Brute force seems to be the way to go, given the level of damage. You'll need a big press. I doubt heat would help much since the key interference is going to be massive, and you can't expand the gear to expand enough to undo it. If the gear was driven by a single pinion, there's a chance the shaft is bent, too. You might want to check how much it's bent and whether the shaft is repairable before investing a lot of time trying to get the shaft out gracefully as opposed to cutting it out and making a new shaft. How are the gear teeth? They need a close inspection given the state of the key.
Some good thoughts, thanks.
Unfortunately the gearbox was opened up, but not protected well and there's some rust on the gears, but no obvious tooth damage.
I guess I could put it in my lathe and see if the shaft is bent.
I've not looked at the pinion.
Yeah figured my 30 ton harbor frate press might not be enough, LOL !
Bob
 
Key and shaft have both been deformed its going to need some hefty gear as John says. Probably going to damage the gear on the way out. Check for twist and bend in shaft.
 
Yes I was figuring no choice but to put it on a big press; just no personal experience with anything big, and damaged like this.

Seems like the kind of deal you take to a shop that has some experience with that kind of thing.

Without the big tools that gears not coming off or going back on.
 
Agree completely. Looking for some insight from those with more experience.
Bob

Well, if it doesn't have a gib key (it obviously does not) or any other retention mechanism then it was pressed on that shaft.

3" wide hub is very narrow for a gear on a shaft that size.

Hopefully the gear being narrow means it will move with less tonnage. Maybe 50 tons will remove and install it.

You might need way more than 50 tons.

I'd feel good about it with a 150 ton horizontal wheel press. A big hydraulic puller might take it apart (but won't get it back together).
 
I did a job lke this......a taperlock had come loose multiple times and the shaft was a mess ........I had to give a written guarantee my repair would not fail............so I filed the shaft to a approximation of round,and made a new hub from a Cummins crankshaft end ......015 interference fit ......heated it up red hot and drove it on with a sledge..........worked great for six months ,then I get a call ,"We cant remove that hub you made ,it wont come off".....Yeah ,right.
 
Send it to Aussie and let CEE get it out. Lol.

As John K mentioned, A place I worked at years back, they would heat shrink half couplings on shafts of about 3" to 5" in diameter with as much as .030" interference with no keyways involved. The only way to get them off was to cut them off.

If they get it off, they better wet mag that shaft where the gear was to make sure the shaft did not "twist" in that wreck.
 
That may not be easily salvageable. If it spun/deformed like that, there may well be a gall raised. If there isn't one now, there almost sure as hell will be by the time you press the shaft for any distance. When we got those kinds of situations, we'd generally drill the key out, then press the shaft out. In the majority of cases, the bore and/or shaft would need to be weld repaired and re-machined or replaced.
 
That may not be easily salvageable. If it spun/deformed like that, there may well be a gall raised. If there isn't one now, there almost sure as hell will be by the time you press the shaft for any distance. When we got those kinds of situations, we'd generally drill the key out, then press the shaft out. In the majority of cases, the bore and/or shaft would need to be weld repaired and re-machined or replaced.
I believe the shat extends out the other side of the gear several inches. Drilling out the key also may not be an easy task.
If I'm understanding your thoughts correctly, the gall is almost akin to a weld. So any gall present would increase the amount of force required to push the shaft out, probably destroying both the bore and the OD of the shaft.
What course of action would you suggest, please ?
Bob
 
I believe the shat extends out the other side of the gear several inches. Drilling out the key also may not be an easy task.
If I'm understanding your thoughts correctly, the gall is almost akin to a weld. So any gall present would increase the amount of force required to push the shaft out, probably destroying both the bore and the OD of the shaft.
What course of action would you suggest, please ?
Bob

Yes, a gall is related to "cold welding" and they usually snowball bigger as you push the two surfaces past each other. There's really not a thing you can do, other than try to minimize the damage. I would absolutely try to drill the key out. Try to drill to a size so that the remaining key wall thickness is barely there on both sides. You may end up breaking through one side... Don't worry about it. After the hole is drilled to depth (either through, or as deep as the keyway) weld a stud to the thick side of the remaining key and use a slide hammer to try to pull it out. Usually after they're collapsed they'll come out this way. After the key is out, all you can do is grind down any obvious protrusions that will interfere with the shaft sliding past the gear, then press it out. Work with what you've got after you find out what happened at the interface.

I wouldn't piss about with a puller, you'll likely snap the gear. You need a press that can support a good solid portion of the hub right near the shaft while it's getting pressed. And it may roach the shaft and/or bore coming off. Not much you can do but repair it. If it's a cast gear just bore it oversize and make a new shaft or build that one up and re-cut it - that choice depends on what it's made of. Guessing it's probably not something like 4140 Q&T or it probably wouldn't have deformed like that.
 
I've had to remove some large shafts from hubs for large fans that come from corrosive environments. There's no pressing them out. We cut the shaft off close to the hub with cutting torches and cut I the remaining shaft out on a horizontal boring mill. A new shaft will have to be made.

First, if the torch cut is on the side I'm machining, I face it off as close as I can the the hub so it's nice and flat.

Then drill it out with an indexable drill

Next, I rough it out by helical interpolation with an indexable high feed mill. Sometimes the keys are held into the shaft with a cap screw, those are super fun!

Finish it up with a boring head, taking it out to close to the hub I.D. until what's remaining of the old shaft is just a thin sleeve. It should thin enough to collapse it and slide right out.
 

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Yup- you're going to need a wheel press for this one. Many of the larger electric motor shop have them. You can try to press it out and if that fails, you can always cut it off and then cut the stub out.
 
nope...never cut or destroy expensive parts without the express written direction of the customer ............. "A mans gotta know his limitations"........say you cant do it and pas the job to someone else.
 
Gotta do what you gotta do. You should always have consent before performing any repair attempt. That's a standard part of the estimation process. If things won't move after the key is out, I have definitely had to put some up and bore the shaft out. Generally in places that didn't have a big enough press, or with something that's flimsy and can't take a heavy pressing, like the above mentioned fan cages.
 








 
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