Couple of pics

[Awhelan]

I know how much everybody likes pics here so even tho its pretty depressing I took a few shots of my latest headache.

Machine: 1980 JD 410. Last fall I had to do rear wheel bearings on one side after they failed catastrophically on the hwy.
This spring the bearings in the other side went! I just got everything back together last Thursday.

Friday afternoon at 4:45 I did this


I didn't notice this had rolled behind the rear tire


Soft ground and nowhere for the wheels to go something had to give!!
FML!

 

[MEK]

Looks like axle was partially cracked, outer edge shows rust and shiny metal was holding until now.

 

[Awhelan]

That's kind of what I was thinking too. When I get this job done and get it back to the shop, I'll clean it up and take some more pics. I'm curious too see everyone's opinion on it.
The Axle had been built up and turned last fall for the new wheel bearing, but only a fraction of an inch of thickness. I'm pretty sure the machinist would have noticed a crack, so that means its new... but I cant think of how it happened. It seemed like it twisted off like nothing tho!

 

[Curbster]

Well, I think we can darn near rule out lack of grease!
Did you have the diff lock on at the time? That rock in the picture should not have caused that to happen, unless it was already cracked badly as I must say the picture does look like an old break with rust on it. My brother the equipment operator, broke an axle on his 81 JD 410 with a full front bucket and diff lock on whilst trying to turn a sharp corner.

 

[Awhelan]

LOL I've never been stingy with the grease! the P.O. was tho and that's what caused all this mess!

My machinist had a look at the axle and he figured the welding and machining process must have weakened it, it twisted off right at the outer edge of the bearing.
He said the ring I'm seeing on the axle is probably the penetration from the weld. To rule out a crack he's gonna cut another thin slice off the shaft to see if the ring continues.
He did warn me last fall when he built the axle up for me that it might not last, but it cost $100 to weld it or $1300 to replace so I went with the cheap route.

I was attempting to back up in the soft ground I was in and with the stone behind the tire the machine never moved an inch! All I heard was a clung and then the fender bent up, I put the hoe down on that side and lifted up to see what happened and the tire just fell over!!

My wife tried to get a few pics of me moving it over to the shop on 3 wheels but it was dark and she was focused on spotting for me and watching for cars.
I'll have to check her phone and see if any turned out.

I did get the job done tho, now the kids can catch and release frogs.

 

[Nige]

Even before you clean the grease off it there are all the classic signs of a high-hour fatigue crack in it. The ratchet marks and beach marks are clear to see. Post some photos when you get it cleaned up though.
It probably started failing from an insufficient radius by the look of it.

 

[Awhelan]

Nige,
Can you explain what " insufficient radius" means? I've never heard that term before.
I'll clean off the grease and get some good pics tonite for you to look at, I'm interested in your opinion on this.

 

[Nige]

Post up the photos of it all cleaned up and I'll try to explain. Also if you had it built up with welding because of damage to the bearing surface it is quite possible that the welding process caused a stress riser that started the crack that led to eventual failure. Generally something like this is built up using metal spraying (arc spray) because it causes less change to the metallurgical properties of the steel than arc welding.

 

[Awhelan]

Pics as promised

 

[Nige]

Sorry to be so long to comment. It really needs a photo from the side after having been disassembled (i.e. with the bearing removed). What I see straight away is what appears to be a distinct change in the material "texture" between the centre core and the outer surface where the bearing mounts. This could be simply the case-hardening process used by the factory but case hardening on a surface normally doesn't go as deep as your photos show. Approximately how much thickness of welding was put on the shaft to build it up when it was repaired..? The centre core of the shaft looks like it's failed in high-cycle fatigue - over a long period of time in other words.

It appears as though the shaft has failed right through the point where the bearing butts up to a shoulder on it. What I'm thinking is that when the shaft was built up and machined maybe the machine shop put too small a radius in the corner where the shaft diameter changes. You can see the bearing has a chamfer in the inside track which is designed to allow the face of the bearing where the numbers are stamped to sit hard up against the shoulder on the shaft without the bearing hitting the radius where the diameter changes from small to large. That lack of radius would immediately create a stress riser and the logical place for the shaft to fail would be right through that point.

Also on your last photo I can see 6 separate dark marks starting from about the 6 o'clock position on the shaft to just past 9 o'clock. This would correspond somewhat to the highest tensile stress area in the shaft caused by the imposed load of the machine down on it. I think they are what's known as ratchet marks and indicate that the shaft was overloaded (maybe by a previous impact) and overstressed. That would initiate a fatigue crack which even with normal loads on it would then continue to grow over time until what was left of the shaft could not support the machine and it failed totally. Obviously your hitting the rock was probably the straw that broke the camel's back but I get the feeling it would have failed at some point in time not much further down the road even if you hadn't hit the rock.

 

[Awhelan]

sorry for the delay - been away on a much needed vacation!
Thanks for the detailed response Nige, Its nice that I can come here and get help from people with some experience and education in this sorta stuff
I think you are right.
The axle was built up I would say approx. 1/8"+- and the radius was re-worked very slightly the machinist was aware of the importance of getting the shaft back to original diameter but he only had the new bearing to use a guide. So it may not have been perfect.

As far as Impacts go, do you think hitting an extremely large pothole while roading would be enough to cause it? (think rear tires airborne at 20mph type pothole)
this happened twice with an ex employee.

All in all I am happy this happened to Me on a job and not an employee on the road! It did kill plans to upgrade this machine this year tho...

 

[Nige]

As far as Impacts go, do you think hitting an extremely large pothole while roading would be enough to cause it? (think rear tires airborne at 20mph type pothole) this happened twice with an ex employee.

I think the answer to that one would be a resounding - Hell yes ..................

That sort of impact would generate extremely high stresses in the shaft and while not enough to fail the shaft in what's known as single-cycle fatigue (right through in one big hit) it would certainly be enough to start the rot for an eventual high-cycle fatigue failure.