Repairing sheared impeller shaft - JD 47 snowblower attachment

[DanMc77]

I have a good friend with the older model 47 snow blower attachment that runs on his 430 tractor. Unfortunately, the shaft that carries the impeller sheared off. And worse yet, JD only sells the entire gearbox for around $1400, not the individual components.

After disassembly, this appears to be a gear on a shaft that is a one-piece part. We were hopeful that the gear and bearing races were pressed onto the shaft with a key holding the gear in place. A machine shop took the part and put it on a 50 ton press and concluded that the shaft and gear are one piece when it didn't budge. I have attached a couple pics of the broken part.

So we're trying to think outside the box and exploring possibilities for repairing the gear/shaft part. The gear and shaft are both hardened.

So here's the question: Has anybody here had any success with repairing something like this? Any clever machinists out there?

 

[jthibodeau89]

I would be surprised that it was 1 piece, but possible. Can you pull the bearings off to see if the shaft to gear face is a square corner or radiused? If radius then likely 1 piece.

But don't give up hope. The gear can be bored and a new shaft pressed and welded in place. Need an aluminum pipe shrunk around OD of gear. Place in a chuck and indicate in the bearing surface of the broken shaft and gear face. Bore the gear and make a mating shaft to fit. Heat gear/feeze shaft and press together. Make provision for locking dowel and press/tig in place. I deliberately didn't suggest a keyway.

Not sure of your skills and tools. If you have to hire out, it may cost more than the gearbox replacement. First step is to confirm if 1pc. Go from there. The other option is to find a used model 47 for parts.

 

[DanMc77]

Thanks for the input!!!!

I am not a deeply experienced machinist, but I fix everything, I'm up for a learning experience, and I have a nice South Bend 13" lathe, so I figured I could put a torch on the hub to anneal the hard shaft, then chuck the other shaft on the other end that's still there and turn down the broken off stub, then bore out the gear until it drops off. I was thinking to bore it out to 2" and get some 2" 4145 stock and turn it down to fit the 2" opening in the gear, followed by turning down to the finished dia needed for the bearings and the shafts themselves. The 2" bore would improve the contact area that's welded. The hardened shaft leaves me concerned. I know that the shaft is stronger if hardened, but also more brittle and that leaves me with concern that the hardness contributed to the failure. So perhaps leave the shaft in it's annealed state. Thoughts?

I have never attempted anything like this, so more experienced insight is very valuable. I hadn't thought of chucking the gear from the outside with an aluminum ring to protect the teeth, so that's very helpful. That makes it possible to bore out the gear in one operation.

We will have to work on getting the bearings off and take a look at what's there with the shaft/gear interface.

 

[jthibodeau89]

I would not anneal the gear before boring. You need everything straight to indicate it in. Just hard turn with carbide tools. Use pre- hardened 100ksi shaft. 50Rc or so. Original gear may only be induction hardened. Core may be soft.

Do not fully weld. Drill and ream a few (3) equally spaced dowel holes that are centered on the split between the shaft and gear. Press dowels below flush and TIG tack in place. Dress tack welds flush. If fully welded it may warp gear, or crack on HAZ boundary.

Instead of making shaft 2", make it 3/16" smaller diameter than the OD of the inner bearing race. This way the shaft and gear are captured by the bearings and cannot walk apart.

Key points: indicate old shaft bearing races true. (may need 4 jaw chuck), avpid excessive heat, press fit shaft to gear and use doweles to lock torque, do not rely on welds to hold together, use geometry to restrain.

 

[jd110]

Parts breakdown shows the shaft is a separate part but is no longer supplied as a separate part. It substitutes to a complete gearbox. It appears if you remove the bearings, there is a snap ring behind one of the bearings holding the gear on. Shaft has a woodruff keyway cut into it to drive the gear. Snap ring is key 26 and shaft is #18. Some parts are still offered individually.

 

[Tinhack]

Too much wasted material and time to carve that out of one piece unless it was a forging to start with. It looks like the shaft broke while turning. Probably due to a locked paddle. Did it ingest a rock or something? Where's the slip clutch?

I agree with boring the shaft out and making a new shaft. I would use a shrink fit with a key. That's probably what the original was. Don't know why your "machine shop" couldn't do that. :confused3: Change machine shops.

 

[jthibodeau89]

Parts breakdown shows the shaft is a separate part but is no longer supplied as a separate part. It substitutes to a complete gearbox. It appears if you remove the bearings, there is a snap ring behind one of the bearings holding the gear on. Shaft has a woodruff keyway cut into it to drive the gear. Snap ring is key 26 and shaft is #18. Some parts are still offered individually.View attachment 680769

Did shaft break on both sides of gear? That shaft appears to have a gear in the middle. Is #18 the impeller shaft?

 

[DanMc77]

Did shaft break on both sides of gear? That shaft appears to have a gear in the middle. Is #18 the impeller shaft?

John Deere does a splendid job at making this difficult to find. Here is an exploded diagram, but this appears to differ from the gearbox on this machine since I don't recall that there are snap rings on the shafts. Anyway, the similarity is there and you can see the gear/shaft listed as one part, indicated by #7.

Edit:>> The impeller attaches to the far side of the gear/shaft part. There's a key, and a bolt that holds the impeller onto the shaft. JD made no provision for a shear point to cover the event when the impeller is instantaneously jammed, so there's a good amount of rotating mass in the drive shaft and solid steel double-V pulley. Looks like this shaft is the shear point. I would be inclined to reassemble without the key, so the bolt can shear. This failure followed a short time after there was an impeller jam caused by some junk wood. <<

I have never done any machining on hardened parts, so this will be good training for me. Use a ceramic carbide cutter??



Here's a link to the JD page:
https://partscatalog.deere.com/jdrc/sidebyside/equipment/74247/referrer/navigation/pgId/11587825

 

[Tinhack]

Have you tested the harness of the shaft? I'm guessing only the teeth are "hard" (above Rockwell 45). Below that shouldn't pose a problem even for off-shore carbide inserts or bits. If you don't have test files, you'll know right away because sparks will fly.

 

[jthibodeau89]

That looks like it is machined as 1 piece. As stated, gears are often only hardened on the teeth. Want the toughness on the shafts. Usually induction hardened.

Did you get the bearings off?

I bought an induction hardening machine for crankshaft pins and mains for my work. Hardened only the face of the journals to about 2.5mm deep. Saw a bunch of interesting machines at the equipment builder, including a large gear tooth hardening machine. By large, i mean a 6' diameter x 8" wide gear. Each tooth was hardened individually. The crankshaft machine was about $1.2 MM back in 2015. The heat cycle took about 2 seconds. But it took a 1600A @ 480V electrical service to run it.