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.