Broke Bush hog

[Overleaf]

I'm a novice tractor owner with an L6060 that I've had for less than a year. While bush hogging the other day with my Land Pride RC 1872 I noticed I wasn't cutting anything. I found my stump jumper with attached blades laying on the ground. The dish looks fine and the blades are ok without any bends. Thank goodness for warranty and KTAC which will fix it even though at this point he had to take the gear box off to take to the shop because the remaining part of the device attached to the gear box spline couldn't be removed yet.

My service guy says he's never seen a break like this. The middle part of the bar is still attached to gear box and the PTO turns fine. I may be cutting with the cutter too low to the ground and there are some stumps around but shouldn't the stump jumper "jump" them.
I guess I want to know if anyone else has ever experienced something like this and what can I do to avoid this situation in the future?
Thanks,

M Koury

 

[hagrid]

Better snaps of the fractures, plz.

 

[85Hokie]

I have seen a bunch of bent ones - never snapped like that, I gonna on a limb and say that steel was treated a bit too much - making it brittle. Then again - I would like to see what the hell you hit!

 

[Overleaf]

Better snaps of the fractures, plz.

This is the best I have. Symmetrical break on both sides. No perceived vibrations any different than normal before the incident. In fact I was probably bush hogging for several minutes before I realized I wasn't doing anything.

 

[mcmxi]

I'm a novice tractor owner with an L6060 that I've had for less than a year. While bush hogging the other day with my Land Pride RC 1872 I noticed I wasn't cutting anything. I found my stump jumper with attached blades laying on the ground. The dish looks fine and the blades are ok without any bends. Thank goodness for warranty and KTAC which will fix it even though at this point he had to take the gear box off to take to the shop because the remaining part of the device attached to the gear box spline couldn't be removed yet.
View attachment 127379
My service guy says he's never seen a break like this. The middle part of the bar is still attached to gear box and the PTO turns fine. I may be cutting with the cutter too low to the ground and there are some stumps around but shouldn't the stump jumper "jump" them.
I guess I want to know if anyone else has ever experienced something like this and what can I do to avoid this situation in the future?
Thanks,

M Koury

Wow! That's impressive! I would think that the stump jumper had to contact something solid that stopped it from rotating in order to cause that failure. What does the underside of the stump jumper look like? I have the RCR1884 with a slip clutch and whatever safety system you have it worked if the PTO is fine.

Do you seen any sign of corrosion at those fracture points that might indicate that a crack was there for a while? We don't know what type of steel is used for that cross member that broke. but looking at the fracture might show some grain structure or other features that indicate some failure in the material processing.

 

[Overleaf]

I have seen a bunch of bent ones - never snapped like that, I gonna on a limb and say that steel was treated a bit too much - making it brittle. Then again - I would like to see what the hell you hit!

I looked all around the area where I found the piece lying on the ground but there was nothing out of the ordinary not even any large stumps. I'm wondering it it just did that after a cumulative total of consecutive bumps. I will admit I was probably cutting too low but other than some stumps there are no large rocks are anything like that.

 

[mcmxi]

I have seen a bunch of bent ones - never snapped like that, I gonna on a limb and say that steel was treated a bit too much - making it brittle. Then again - I would like to see what the hell you hit!

That failure is a double shear case which makes it even more impressive. As you say, surely there's an issue with the steel used. Is it high carbon or mild ... who knows? I would expect mild steel to be used in this application.

 

[Overleaf]

Wow! That's impressive! I would think that the stump jumper had to contact something solid that stopped it from rotating in order to cause that failure. What does the underside of the stump jumper look like? I have the RCR1884 with a slip clutch and whatever safety system you have it worked if the PTO is fine.

Do you seen any sign of corrosion at those fracture points that might indicate that a crack was there for a while? We don't know what type of steel is used for that cross member that broke. but looking at the fracture might show some grain structure or other features that indicate some failure in the material processing.

The stump jumper looks fine on both sides. In fact I thought they would just replace the cross member but I guess due to balance and other factors they replace the whole thing. I see no corrosion--Its only a few months old--I bought new. The metal at break looks grainy to me. Almost like pot metal but I'm sure its better than that. I posted another pic and you can see the fracture which is identical on both sides.

 

[mcmxi]

The stump jumper looks fine on both sides. In fact I thought they would just replace the cross member but I guess due to balance and other factors they replace the whole thing. I see no corrosion--Its only a few months old--I bought new. The metal at break looks grainy to me. Almost like pot metal but I'm sure its better than that. I posted another pic and you can see the fracture which is identical on both sides.

My comment re corrosion is that sometimes you'll see rust on part of the fracture interface indicating that the crack took a while to propagate, but the photo you posted does look like a clean surface indicative of fast fracture. Unfortunately you'll probably never know why the cross member failed. Was the heat treat incorrect, did the welds affect the heat treat of the steel, do the welds add a stress riser near the failure, was the wrong type of steel used, etc.

I've used my RCR1884 for a few years and it's had a tough life, and other than putting dings in the blades, and a couple in the deck, it's still going strong.

 

[Overleaf]

Here's a up close pic of the break that might show the structure of the metal better.

My service guy couldn't get the rest of the cross bar off the shaft. Ended up cutting it off on both sides and taking the gear box off to take back to shop. After heating may need new seal.

 

[rbargeron]

I edited my post now that I see how the blades are attached. Sure looks like the center bar had a ton of residual stress from being cold bent to shape. Mild steel would stand it but whatever this is has to be annealed before that much bending. Heat treating can be good, but only AFTER all the forming is done.

 

[Flintknapper]

You didn't do anything wrong. Without question the metal cross-bar is/was inferior. You need only look at the crystalline structure of the metal grain to confirm.

The type of 'shear' that occurred there simply would not be possible for any other reason.

 

[mcmxi]

I'm thinking the way the blades are attached may have caused them to wedge against the drive bar breaking it. Is there a spacer or a rounded back end of the blade so it can swing freely without binding?

Here's a schematic from the 1884 parts manual which is the same family as the 1872. Notice the bend in the cross member which is where the failure occurred as shown above.

 

[Overleaf]

You guys are making me feel better. I'm coming around to your thinking that the metal failed. It was so atraumatic when it happened that I mowed for awhile until I realized I wasn't.

Thanks for everyone's input.

 

[GrizBota]

I agree with the assessment of the steel being sub par. I have an RCR 1860 that I’ve beat mercilessly for hundreds of hours. I’ve broken everything except the cross bar on mine, skirt, skids, gear box, blades, tail wheel, tail wheel bracket assembly, cracked stock welds on the deck, etc. My millwright buddy welds it up for me and I provide the steel and paint.

A picture of the survivor, post most recent welding repair, pre paint.

As to running it “too low” you can drag it on the ground if you want. That’s why LP makes replaceable skids for them (if you don’t have a set, get sone and mount them up). I set mine a finger width above the concrete floor everytime I leave the barn. So mine probably drags as often as not because I’m on anything but smooth ground.

If you do mow low, be mindful of making tight turns with the deck low because if it snags the ground, it can be hard on the three point linkages.

A picture of the survivor, post most recent welding repair, pre paint.

 

[skeets]

Not a welder by any means or a metallurgist, but does the shear look like kind of crystalised ?

 

[GeoHorn]

It reminds me of an airplane engine mount I once observed that the mfr’r analyzed as “resonance-fracture”. The discussion was in regard to a piston engine which had an improperly “dampered” (counterweighted) crank which transmitted vibrations that fractured the steel mount. The actual fracture had a similar appearance to this broken crossbar.

 

[mcmxi]

Not a welder by any means or a metallurgist, but does the shear look like kind of crystalised ?

The fracture surface does look crystalline and consistent with a brittle fracture. High resolution images would be interesting.

Heat treat in this part would be for the purpose of stress relieving after adding those bends in such thick material, which would result in a lot of residual stress. My guess is that the bar is a mild steel alloy such as A36 or similar that's cut to length, drilled and bent in a large press, and then stress relieved. A stress relief cycle would require heating the part to a certain temperature range, holding it at that range for a specific period of time, and then allowing the part to air cool. Lots of ways to get it wrong.

This is a really good book for those that want to learn about this sort of thing. According to Amazon I bought this book in 2020 which was shortly after I took a 3-week blacksmithing class.

Steel-Metallurgy for the Non-Metallurgist

 

[skeets]

Wish there was a blacksmithing class around here,, not interested in becoming a farrier, but learn to heat and bend some iron. A Brother has a full black smiths shop at his farm, his G Grand Father was the last one to use it when they still used horses. He said I could use it but I would like to have an idea what I was doing before I mucked something up.. lol