Remove Large gear from shaft - damaged key

[MillGuy88]

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.

Absolutely correct. You'll want to get written consent before turning the shaft into a pile of chips.

 

[farmersamm]

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.

I agree on cutting the shaft.

But here's where I do it a bit different. Cut the shaft so that it's near flush with the face of the gear on both sides. Then simply cut out the center of the shaft. No need for fancy machining. It can be washed out with a torch.

Cut center of shaft out, then move torch to one side to cut a slot up to the ID of the gear. If you are good with the torch, the damage to the bore is minimal, or non existent.. If you're squeamish about slotting, just cut out the bulk of the center, and hope that the heating/cooling will allow the press to do its work.

Then you can fool around with a press to push the shell of the shaft out. Most people rely on presses too much. The real work is done with heating, or cutting.

You can get an appropriate size tip for your O/A to pierce the center, then simply do a swirly to enlarge the hole.

IMHO

 

[eKretz]

I agree on cutting the shaft.

But here's where I do it a bit different. Cut the shaft so that it's near flush with the face of the gear on both sides. Then simply cut out the center of the shaft. No need for fancy machining. It can be washed out with a torch.

Cut center of shaft out, then move torch to one side to cut a slot up to the ID of the gear. If you are good with the torch, the damage to the bore is minimal, or non existent.. If you're squeamish about slotting, just cut out the bulk of the center, and hope that the heating/cooling will allow the press to do its work.

Then you can fool around with a press to push the shell of the shaft out. Most people rely on presses too much. The real work is done with heating, or cutting.

You can get an appropriate size tip for your O/A to pierce the center, then simply do a swirly to enlarge the hole.

IMHO

Dangerous with a cast webbed gear. Likely to crack if heated only near the hub.

 

[farmersamm]

Dangerous with a cast webbed gear. Likely to crack if heated only near the hub.

You're not putting excessive heat into the hub/bore...........you're removing the steel shaft. As the shaft is cut, the tension on the gear is reduced because the shaft is being hollowed out. This is a fairly common procedure.

To be fair.............it's a welder thing, not a machining guy thing, so I understand the worry. Believe me, it's misplaced.

 

[eKretz]

You're not putting excessive heat into the hub/bore...........you're removing the steel shaft. As the shaft is cut, the tension on the gear is reduced because the shaft is being hollowed out. This is a fairly common procedure.

To be fair.............it's a welder thing, not a machining guy thing, so I understand the worry. Believe me, it's misplaced.

It's not misplaced. I've seen it happen. I used to supervise a very large shop full of machinists, millwrights, and welders. On a large shaft material can not be removed fast enough with a cutting torch to prevent thermal expansion. On something tiny, perhaps. Many types of iron don't have the same give as steel.

 

[farmersamm]

Aw bullshit (big grin)

Heating a CAST IRON(possibly semi steel, which is cast iron) hub to remove it.

If'n you don't believe it's cast iron......look at the chips when it's being faced.

So.........here you have a piece of cast that's been MONDO heated to remove it from a shaft. And it didn't suffer the Crack Of Doom. This stuff is more resilient than most folks think. You start getting into stress factors when brazing, or welding, cast........which is done at a much higher heat.

And there's the Universal Rule...............When it's broke, it can't get any broker LOL.

Do something like this if there's a better alternative?........No. But if you need to save a shaft that's a high dollar shaft, you do what's necessary.

Cutting a shaft out of the center of gear doesn't come near to the point of ruining it.

I gotta read back over the thread......................But do we know it's a cast iron gear??

 

[john.k]

If it is cast ,its ductile or meehanite,and take a lot more force and shock than grey iron.

 

[Overland]

I don't know what material the gear is.
Bob

 

[eKretz]

Aw bullshit (big grin)

Heating a CAST IRON(possibly semi steel, which is cast iron) hub to remove it.

If'n you don't believe it's cast iron......look at the chips when it's being faced.

So.........here you have a piece of cast that's been MONDO heated to remove it from a shaft. And it didn't suffer the Crack Of Doom. This stuff is more resilient than most folks think. You start getting into stress factors when brazing, or welding, cast........which is done at a much higher heat.

And there's the Universal Rule...............When it's broke, it can't get any broker LOL.

Do something like this if there's a better alternative?........No. But if you need to save a shaft that's a high dollar shaft, you do what's necessary.

Cutting a shaft out of the center of gear doesn't come near to the point of ruining it.

I gotta read back over the thread......................But do we know it's a cast iron gear??

No; and it's not about HEATING the iron. It's about heating the inside area faster than the outside mass can expand. Which can result in cracks in the web. Again, depending on the type of iron (as I already mentioned), this absolutely can happen. And your universal rule is dead wrong. Needing to make a whole new gear of that size is very much more broken than needing to bore it to cleanup. You do it your way, I'll do it mine.

 

[gbent]

Something else broke that they disassembled the gearbox. That little bit of sheared key didn't cause anything to not work to where they needed to tear into the box. If that is truly all that is wrong, I'm with John K on this one and run it until something else breaks.

Estimate 10 tons per inch shaft diameter for normal press fits. This could easily go 3 times that amount.

One problem with burning the shaft off to drill it off the gear is it makes reverse engineering much more difficult. Its lots easier to make up the length for a bandsaw cut. Better have the owner check on availability and cost of a replacement shaft, that may factor into whether you run it or not as is.

 

[Gearclash]

Haven’t seen anyone mention this yet -- having only a square key is typically not the method of choice to transmit rotational force between parts on a reversing drivetrain.

Another thought -- the shaft DID move in the gear, so it can, in theory, be made to move again.

 

[MillGuy88]

You can try and press it out with the biggest and baddest press you can find, but do not damage the gear.

If that doesn't work, cut the shaft out. It's a lot cheaper to replace the shaft than the gear. If you can, try to source a drawing of the original shaft. I've had the luxury of having access to the original drawings because the mine it came from owns them.

 

[memphisjed]

I think I see fat fit on that. Whatever means to drill out key key without to much damage to shaft in key area. I think once key is out some force and turning will get gear off. Somewhere between some and lots, not brute force level.
Fill in old key way, turn shaft 90 and mill new one.
Reassemble, get paid.

 

[eKretz]

Also, use a lot of anti-seize when it's re-fitted. It really does help reduce galling.

 

[4GSR]

I'm not a fan of blowing out a hole in the end of the shaft with a torch. Be much easier to drill & bore the shaft out a bit. Doesn't have to be all the way out to the ID of the gear, just get some of the mass out of the ID. Once doing that, a 10 ton shop press will probably push out the rest. The bugger is the shifted key. Even drilling it and punching it out may/may not work. Alternate would be after boring out the shaft, Run a series of weld beads in the ID of the fish, let it cool, and it should drop out easily.
Before cutting the shaft, get a accurate overall length of it! Won't be able to do that easily afterwards. Had the shop do that to me several times in the past.

 

[candeservices]

I seems to me that ALOT o heat and force will be required but any way you go. The Gods WILL want blood.

 

[hvnlymachining]

I recently did a nearly identical job, but 3-7/16" shaft with a fully sheared key, made a couple rounds before coming to a stop. It was galled enough to require welding repairs to both the shaft and the coupler after disassembly.
I was able to use some heat and a Posi-Lock model 116 puller to get it off.

 

[michiganbuck]

first I would make a close jack puller.
1" by 2" x perhaps 4" long (?). Hand grind / hack oneend to full- fill the open half moon cavity in the key slot. Have a 3/8 or 1/2" screw thread .enough away from the shaft so you can get a wrench on it so pointing toward the key end. Crank away pushing because the small tag holding likely is not as strong and the screw cam push...likely shear off the little what is holding with almost no damage to parts.
Yes a good steel and a higher grade screw.
likely ger a 6k to 10k push with the right screw and steel. Put some shims in to keep it straight/

 

[just Dave]

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.

Some good suggestions here some bad. Drilling out a captured key is ridiculous . The shaft is extensive, having a grinding element past the bearing and the whole thing in some sort of housing .
Does the customer want repairs done in place or tear down?
I would bar over the grinder and measure run out of gear now.
I would advise that in place removal will likely leave shaft in an unusable as is condition, requiring a time consuming and expensive in place repair of the fit for the gear.
Typically a grinder like I think you’re talking about will have circuit protection to kick out the motor in a jam and require an Operator to reset and manually hit reverse to clear.
If this is a hammer- mill, more often seen handling scrap wood and metal, it may well be a tapered fit for the gear.
I really need more info on the problem, Will it not run as is?

 

[MillGuy88]

Here's another example of a massive trunnion wheel I had to get the shaft out of. The hub is shrink fitted onto the shaft. Trying to heat up the hub while keeping the shaft from expanding at the same time to try and get it out is virtually impossible.

It's quicker and easier in this instance to cut the shaft out. Plus it's already in the machine to check out of round and take a skim cut to true up the bore.