Dipper snapped

[Tarmy]

So…this issue had me wondering about my rig. This pic is from the same area as OP…and I noticed on the factory installed dipper area attachment for the thumb a small plate. It looks like it is there to stop this kind of fracture. OP’s is after market bolt on…and may have added stress to an area not accounted for in the arm without the thumb.

 

[JRHill]

I had trouble with the cross bar above the bucket on the loader. It had been welded previously before I owned the tractor. I welded it up and it broke again so I ground ALL the old stuff off, gave myself some chamfer and made a root pass then another on each side of the root with zero undercut. Then I fired up the rosebud and heated to whole area to barely red and kept playing the torch over the area so it cooled slowly for stress relief. Didn't gusset it and 25 years later it is just fine so it was worth the time to do it right.

Gosh that old B7100 has been a workhorse for me.

 

[JohnDB]

So…this issue had me wondering about my rig. This pic is from the same area as OP…and I noticed on the factory installed dipper area attachment for the thumb a small plate. It looks like it is there to stop this kind of fracture. OP’s is after market bolt on…and may have added stress to an area not accounted for in the arm without the thumb....

Surprised if that is Kubota factory welding. That small plate doesn't look to me as though it was designed with the same care as the plates on the rest of the dipper. And I can't help wondering about this:

I agree with @ruger1980 that best practice would have been to end the bead in the OP's photo extended from the reinforcement and then grind the puddle flush.

I still think this is likely to be higher tensile than mild steel. EDIT: Does anyone have workshop manual that covers repairs to these machines? If so what does it say?

 

[Tarmy]

Surprised if that is Kubota factory welding. That small plate doesn't look to me as though it was designed with the same care as the plates on the rest of the dipper. And I can't help wondering about this:
View attachment 168578

I agree with @ruger1980 that best practice would have been to end the bead in the OP's photo extended from the reinforcement and then grind the puddle flush.

I still think this is likely to be higher tensile than mild steel. EDIT: Does anyone have workshop manual that covers repairs to these machines? If so what does it say?

Just grease dripping off the fittings above that.

And yes, crap looking factory welds on my BH…bought new with tractor…

 

[ruger1980]

I still think this is likely to be higher tensile than mild steel. EDIT: Does anyone have workshop manual that covers repairs to these machines? If so what does it say?

"Mild steel" is a very broad term and I referred to structural steels. The main steel the excavators I work with are fabricated with grades of steel comparable to A656 steels. Generally in 70k psi tensile range, so nothing extreme.

The thumb mount in @Tarmy's pic adds a lot of stiffening to the area where the OP''s stick broke.

I also wonder if the backhoe attachments are built in the same facility that the loader attachments are here in the US.

 

[selftot]

That small reinforcement plate could be an afterthought. Maybe added after sticks started getting broken on dippers with the thumb.

I've been thinking that my bolt-on thumb stiffened my dipper so all the stress got focused on the location that failed. Probably contributes to the problem.

 

[Yooper]

Just asked AI what steel is used on Kubota backhoes and it said A36. I am skeptical.

 

[Hugo Habicht]

Just asked AI what steel is used on Kubota backhoes and it said A36. I am skeptical.

There is no such thing as AI. What clueless journalists typically refer to as "Artificial Intelligence Stupidity" is just some form of sophisticated internet search (or digital image or sound processing we had in the 60s). With the majority of internet content being outdated or plain wrong at this stage I would not waste my time on using such software.

 

[JohnDB]

Just asked AI what steel is used on Kubota backhoes and it said A36. I am skeptical.

I agree, A36 seems very basic but maybe cheap and easy was the designer's motto. Looking at the fracture surface I'd say its something stronger than that, as @ruger1980 mentioned. Just googled T1 steel that you mentioned... but I don't think it would be that, based on the description.

There is no such thing as AI. ... With the majority of internet content being outdated or plain wrong at this stage I would not waste my time on using such software.

AI saved me a lot of time in the last couple of days solving 2 different internet connection problems. I was stunned at how effective it was. It also told me how to use an old router as a cabled wifi extender - simple solution, simple instructions, worked first time. That was after I'd tried to research the solution on the internet and got fed up because google had turned up enormous volumes of conflicting material.

Now back to the dipper stiffening issue...

 

[Runs With Scissors]

Now back to the dipper stiffening issue...

SOLVED!!!!!

Sorry…..(but when you ‘loft softballs” in the air, it’s tough not to swing at them )

 

[Yooper]

My guess is that it is grade 50 or better. That would be in the structural steel category. The reason I suggested T1 for the gusset was purely from a strength standpoint. I used it to strengthen a forklift backstop that a business was always chaining heavy equipment to and pulling with it. Pretty much twice the strength of A36 and very weldable. It does not form well though.

 

[hagrid]

Presuming an electric arc process, what electrode/wire shall we choose?

 

[chim]

Surprised if that is Kubota factory welding. That small plate doesn't look to me as though it was designed with the same care as the plates on the rest of the dipper. And I can't help wondering about this:
View attachment 168578

I agree with @ruger1980 that best practice would have been to end the bead in the OP's photo extended from the reinforcement and then grind the puddle flush.

I still think this is likely to be higher tensile than mild steel. EDIT: Does anyone have workshop manual that covers repairs to these machines? If so what does it say?

The reinforcement above the yellow arrow and the mount for the thumb below the yellow arrow would stiffen the boom on both sides of the arrow. The little bit of steel of the thumb mount that bridges the otherwise un-reinforced area probably doesn't contribute very much making the structure weaker in one spot.

 

[selftot]

My welder had a different plan. He started with some plates on the inside then added 2 on the outside..

I probably would have moved the re-enforcement in the direction of the yellow arrow. Maybe he was trying to avoid the thumb.

He extended the plate on the other side to re-enforce where the thumb bolts were pressing into the dipper.

I'm happy with it especially for $350 but I'm curious what comments will follow.

 

[North Idaho Wolfman]

My welder had a different plan. He started with some plates on the inside then added 2 on the outside..

I probably would have moved the re-enforcement in the direction of the yellow arrow. Maybe he was trying to avoid the thumb.

View attachment 168699

He extended the plate on the other side to re-enforce where the thumb bolts were pressing into the dipper.

View attachment 168700

I'm happy with it especially for $350 but I'm curious what comments will follow.

Is it straight?
If it is then you're good to go.
Just don't break it again!

 

[McMXi]

My welder had a different plan. He started with some plates on the inside then added 2 on the outside..

I probably would have moved the re-enforcement in the direction of the yellow arrow. Maybe he was trying to avoid the thumb.

View attachment 168699

He extended the plate on the other side to re-enforce where the thumb bolts were pressing into the dipper.

View attachment 168700

I'm happy with it especially for $350 but I'm curious what comments will follow.

As I said earlier, lots of ways to fix this and from where I sit I see no problem with the fix or the cost to fix. Is it how I would have done it. Maybe, and maybe not, but the plates look good, the welds look good, and I very much doubt you'll ever have a problem with that part again which is what matters.

 

[selftot]

Just don't break it again!

Double dare ?

 

[John T]

Easy does it....

 

[GeoHorn]

I'm an amateur but this is what i came up with. Probably overkill and wrong shape. And wrong location. lol.
Would appreciate any feedback.

View attachment 168461

Steel is strong in tension… not so much in compression.

Thinking of how that arm is stressed when under load…. causes me to believe that a patch which, either proceeds around the corner and onto the adjacent surface (such as angle-iron-shape)… OR an Added-patch covering that cracked area on that side.

 

[GreensvilleJay]

Easy does it....

View attachment 168722

Looks like those notches were caused by the thumb mounting bolt ? If so, the 'patch plate' could have been longer ,past the notches.