yet another thumb on its way

[two_bit_score]

Wow two broken dipperstick threads back to back. Glad you got it back going.

 

[davcog]

I am glad you took the time to post an update on this build after three years. It is important to let us know about problems like this with a build. it helps the rest of us take into consideration things you learned the hard way. Thanks again.

Ditto!:drink: Have been researching web for info on thumbs builds for BX 23.

 

[workinallthetime]

you cant tell it from the pic's but for those who want to know the cracks were in the middle of the dipperstick around the upper mount for my thumb. the bottom attachment point has had no issues. if i was going to do it all over i would start out with both points being "boxed" in completly around the dipper stick and no less than a foot long all the way around. that way you would spread the pressure out.

 

[roman]

Hey workinallthetime. Thanks for a thorough job and post. You are a true craftsman and excellent reporter too. I want to learn welding someday...

I just picked up a used woods bh w/subframe. I am considering a thumb. Can anyone give me pros and cons for bolt-on type vs welded?

thanks,
Roman

 

[easygo]

If you follow the way the bending force acts on the dipper stick it is no real surprise that it broke near the top mount for the thumb. It appears that the crack started heat effected zone of the factory weld.

When you pick up a rock and the bucket pinches it against the thumb the pressure of holding said rock is instantly transfered to the top mount attachment point and trying to bend the dipper stick. Eventually it did.

 

[workinallthetime]

If you follow the way the bending force acts on the dipper stick it is no real surprise that it broke near the top mount for the thumb. It appears that the crack started heat effected zone of the factory weld.

When you pick up a rock and the bucket pinches it against the thumb the pressure of holding said rock is instantly transfered to the top mount attachment point and trying to bend the dipper stick. Eventually it did.

the second set of cracks started there, notice the square block in the first pic and its location. this block was welded in place to cover the first set of cracks that happened. There is no doubt in my mind about the what and the why's that caused this failure. The unit was never intended to do this type of work!
I would hope that others considering this type of mod would learn from my experience, design due to my experience and operate due to my experience. i use my tractor way beyond what kubota ever designed it for, but after this i am going to have to do a little more consideration besides the <yes> it will pick it up and the <no> to heavy. lol

 

[ak9]

workinallthetime
I agree these type of BH are easy to break if your not careful . It does'nt take much sometimes . I totally smashed a 16" bucket with only about 4-5 hrs on it ( not built strong by manufacture 1/8 " material was used ) and a week later an outrigger snapped in half on the same bh !I would have also bought a different brand if I could do over. So when I built my bh thumb a couple years ago I did it using a linkage system that put the force parallel to the dipper stick ,also doing this way I was able to collapse it to the dipper. So far it has'nt broke ,time will tell
easygo you are exactly right about the stresses ...

ak9

 

[ptgdigger]

I don't want to be a killjoy here , but when adding thumbs or other attachments welded to the boom or dipper , never, never ,never weld horizontally across the stick. If you look at how almost all backhoes and even loaders are designed any attachments or gusset plates are almost always "fish plates" , in other words the ends that would be horizontal or "across the stick" are extended in to a fish head shape or diamond shape. This helps avoid the resulting weakness from the weld being in a straight line which will easily crack.

When making a thumb bracket always use a backer plate and weld the sides only, if you really feel you must weld the top or bottom make it a fish plate ^ <>

Ray

 

[ptgdigger]

To the original poster please don't take this as me picking on you , I'd just really hate to see this happen to someone else who doesn't have the ability to easily fix it as you did.

The second cause of failure here is the extreme angle the strong arm is working against the stick:

Much better to have your strongarm trying to shear the upper bracket off the stick rather than pushing it into the stick:

Even better would be to lengthen the strongarm to get the upper bracket up into the reinforced area of the boom, but that is probably overkill.

One that I did recently, see how the arm looks like it's trying to tear the bracket off the stick rather than pushing it in:

Ray

 

[davygp38]

A picture is worth a thousand words, but this one was worth a bit more. Good side by side comparison.