(This isn’t specific to backhoes, not sure where to post. ) The 1.25” hardened steel , spindle in the picture is from a bush hog. It snapped when a rock was hit. My question is: can this be welded and repaired? My guess is that due to required working strength and stress it can’t be repaired.
No way in this life for there to be a proper weld repair of that in my opinion. Should be able to purchase that spindle. Bush Hog 71316 Output Shaft Looks to be around $250.00.
Something failed to do it's job. If it has a shear bolt you must have had the wrong grade bolt. If it has a slip clutch you needed to service and adjust it before use every year. They will rust together over time. Slip clutches need to be taken all the way apart, cleaned up, and adjusted. Bare minimum they need to be loosened and spun then readjusted. What size bush hog is it? Does it have a smooth input or splined with a clutch? You can get a whole new 45HP gearbox with a shear pin type input from Agri Supply for $275. https://www.agrisupply.com/45hp-gearbox-f-105961-105962/p/121221/
I did buy that new spindle and a few support pieces for $320. I was just wondering if it could be fixed . For some reason, I hadn’t considered that the slip clutch would have prevented this if it was adjusted properly. Thanks for pointing that out. I’ll get on it. It’s a Bush Hog Squealer 72. I wasn’t operating it when it broke but they hit a big rock , hard and fast.
Could it be fixed sorta would it last absolutely not. Dad welded at a machine shop they did alot of shaft repair and I've been slowly learning. Gets out of lots of pickles but not this one.
That shaft was mostly failed months ago, probably out of dynamic balance by the rusted crack on two sides instead of equal all the way around. Whatever they hit was just the first thing that overloaded the center portion that was still holding on, it would have failed in a few hours just running without any grass at all. IT MAY HAVE hit a big rock months ago that bent it, and it possibly could have been straightened and lived.
Delmer's right. That rock was just the straw that broke the camel's back. The failure started a long time ago judging by the look of the fracture face.
That’s interesting that the damage to the shaft could have been done long ago. They have been hitting rocks with it for years! Are the ellipse patterns visible on the broken steel from the hardening process or from the external stress that caused the break ? Now I recall that this past summer the operator complained that the brush hog’s clutch was ‘making a weird smell’ , it was slipping and getting hot when they were trying to mow long wet field grass. I then tightened up each of the eight nuts on the slip clutch a small amount (1/2 turn ? don’t recall) . Maybe I went too far and made it too tight. The owners manual for the slip clutch has complicated procedure to set the tension on these slip clutches. I need to come up with a simple way check that they give way at the right point, guessing isn’t good enough. Maybe restraining the mower blades and easing on the pto would work.
The really fine and smooth lines in the fracture are old. Its gradually progressed inwards. The rock that snapped it caused that rough fracture in the middle.
The failure mode is known as high-cycle fatigue. Basically what happens is that a load greater than the component (shaft in this case) is designed to handle is imposed on it. The imposed load is NOT enough to fracture the shaft immediately. That overloading starts a minute crack somewhere that slowly develops over time (could be anything from 1k-10k load cycles) until whatever is left the (rough area in the middle) is not capable of withstanding normal loads (or hitting a rock in this case) and shears off. The fine lines top & bottom of the photo are "beach marks" (white arrows), a comparison to the way the sea makes lines in the sand. Maybe with some decent photos of the fracture face "ratchet marks" (red arrow I think shows some) would be more visible. A ratchet mark indicates the first part of the shaft that started to fail. I would say that the failure started in multiple locations around the circumfrence in the root of the radius between the smaller and the larger shaft diameters.
Could be the clutch discs are glazed and beyond usefulness. You might want to replace those when you service it. You are lucky the failure occured at the mower end and not the tractor.
The clutch smelling when being overloaded in tall wet grass is a GOOD sign. That means the clutch was working correctly. It shouldn't have been tightened, but that probably didn't cause this. Rotary mowers are designed to hit crap, even rocks, and survive. There may have been one big collision that torqued this shaft that Nige was looking for the evidence of, or the shaft could have been bent just from the turtle hitting a rock, not the rotational shock, or it could have been run too long with a blade missing, bent, or loaded up with baler twine causing imbalance. It's near certain that the corner contributed to the stress concentration, and most of the failure was high cycle fatigue, and probably from imbalance. Just a guess that it was months, that would be impossible to know. It wasn't a day, it could have been a year or more?
It seems replacing it likely to be faster than an anneal, weld, normalize, heat treat process. I would love to see some 8x cameraphone shots of that spot where it started, perhaps the tool that made the radius went a bit too deep and caused a sharp edge / stress riser.
What caused that failure where it is, was a sharp edge to the collar. When making a shaft you should always bevel a step a little or it will be prone to fracture at the step edge every time. It does make it hard for a bearing surface but still should be done.
Probably want to check the gears in the gear box for damage. Slip clutches can be hard to adjust just right and they recommend loosening them off every year because they are known to rust up. A rusted or too tight slip clutch from a year or more ago could have caused the initial damage and a good hit even with the clutch not stuck could cause catastrophic damage. If the blade(s) was more heavily damaged or even very poorly sharpened throwing it way out of balance could have contributed to the failure. PTO mowers aren't as critical for balancing but still good to be close. My dad sold commercial mowers for 40+ years. His mechanic and him did an experiment with a walk behind mower by taping a quarter to the end of one side of the blade. Mower basically self destructed in short order. Less than 2 minutes if I recall. Interesting in his long career, he never had an incident involving a mower.
Thats what I was thinking, suppose if its going to have a small radius, double the size of the shaft!
How many hours are on that shaft? That kind of stuff is pretty normal for that type of work. If it is the first broken shaft, there isn't enough information to make any changes in operation or design. The cost of the shaft is not excessive and probably isn't that difficult to change. Get a new one and go back to work. Track usage and then consider what to do.
It may have been oversized to help compensate but sometimes no matter how heavy duty something is designed, there will be a careless operator or hidden obstacle that failure is imminent. To attempt to fix the shaft wouldn't be worth even considering. Definitely need to fully inspect the gears in the gear box for damage. Magna flux or dye penetrant wouldn't be a bad idea. I say this because I took out a gear in a PTO driven rototiller.
That Bush Hog Squealer 72 is probably 8 years old and as far as I know , this was the original gear shaft and 2nd set of blades. I replaced the two bearings and seal on the shaft 3 years ago. When I had it apart recently to put in the new shaft , the gears looked I damaged but I couldn’t have seen hairline cracks .
Would hate to replace the shaft only to have the gearbox break.