Kubota BH75 Damaged by bolt-on Thumb

[MacPDaddy]

I really need some advice.
I saw the backhoe thumbs and thought it would be a great addition to my BH75 backhoe. After doing a little research, it came down to a bolt on model sold by Extreme Metal Products (Ebay for $325).
The thumb arrived and looked really nice, excellent fabrication and very tough.
After a short period of use I inspected the position of the thumb to insure it did not slide (a problem noted for the Wallenstein type design), it had not.

PROBLEM: I noticed that the hydraulic fitting on the cylinder was actually hitting the dipper arm, after pulling the thumb off, I noticed the dipper arm itself actually had a bend in it!!
The arm had a compression mark on the underside where the thumb bracket pressed against it and a dent in the top where the bolt closer to the bucket actually pressed into the arm.
At this point I will need to replace the dipper arm (Kubota part is $622 from tractorsmart.com).

QUESTION: Has ANYONE noticed an issue with bending a dipper arm, no matter how slight with one of these clamp on type thumbs (EMP, Wallenstein, or Bro-Tek)?

My assumption is that the bucket pressure pushes on the thumb and the resulting force is against the arm at it's mid point. I did check on the Kubota factory thumb for the BH65 and the support strut actually connects high up on the arm allowing the force to be directed up the arm rather than against it (no bending force on the dipper arm itself). I just find it hard to believe that I am the only poor soul who has seen this. Upon close inspection, the dipper arm is pretty thin steel.

I have one fallback I am hoping works out. I may end up having an arm fabricated by my father-in-law with a heavier gauge steel.
I still want a thumb, very handy item, I just need to understand why this happened and insure I can use one without damage.

[dfkrug]

You are right about the thin steel on the dipper stick. My hoes are only
3/16". I was VERY concerned about distortion of my dipper when I designed
my thumbs. A welded on thumb is a much safer bet, IMO. The two
weldments I use distribute the force over a wide area and the one at the
end of the dipper wraps around the dipper. You can see my pix if you go
to my photo links.

Post a photo of your damage so we can look at it.

[john_bud]

I would not replace simply due to a ding. You can weld on some fish plate (or have it done) to make it strong. No big deal. Hoes are meant to be broken (at least mine thinks so!!).

jb

[MacPDaddy]

I managed not to get pictures of the actual damage. I do have pics of the bolt on thumb installed. My father in law has built a new arm for me, so I get to see it this weekend to insure everything is good before he welds it all up.
I will have a thumb attached by installing a new tube inside the arm and putting the brace far up the arm like the BH65 has factory installed. Should be no more issues with bends. The new arm will be made of 1/4" steel tube. I will post pics of it this week. I'm out $40 for the steel and owe a favor to the FIL. He said it would take a while, 5 days isn't long in my book. BTW, I will post the thumb on Ebay as I won't need the bolt on!!!

[dfkrug]

Originally Posted by john_bud

Hoes are meant to be broken (at least mine thinks so!!).

JB, have you broken something on your massive rebuilt b/h? Or would you
rather not talk about it? :-)

[MacPDaddy]

OK, I've got some pics pre-damaged time. Just after I so proudly installed the thumb (I will be selling the bolt on thumb now, with warnings for usage!!)

[MacPDaddy]

Originally Posted by john_bud

I would not replace simply due to a ding. You can weld on some fish plate (or have it done) to make it strong. No big deal. Hoes are meant to be broken (at least mine thinks so!!).

jb

It rippled pretty bad once straightened, decided to go for a stronger arm with 1/4" steel (vs. 1/8" Kubota uses). The bend was enough the cylinder hit the arm and there was twist as well. The twist was caused by a log off center. My inexperience with thumbs played into that part of the issue. As they always say, hindsight......

[MacPDaddy]

Originally Posted by dfkrug

You are right about the thin steel on the dipper stick. My hoes are only
3/16". I was VERY concerned about distortion of my dipper when I designed
my thumbs. A welded on thumb is a much safer bet, IMO. The two
weldments I use distribute the force over a wide area and the one at the
end of the dipper wraps around the dipper. You can see my pix if you go
to my photo links.

Post a photo of your damage so we can look at it.

Very nice work, I may get a hold of you for some advice once I get the arm back later this week. We are adding thumb connection points directly to the arm like the BH65 connection points. May need some help designing the thumb. We are adding a tube just up (2.5" inches roughly) from the bucket connection points. The support will attach just about where yours does.

[MacPDaddy]

Roger brought the arm this weekend for a trial fit to insure it worked before he completed the welding.
Everything fit together, the original pin sleeves were re-used and the 2 upper plates were also re-used.

It's back off now to get fully welded and have the thumb connections added.
Once it's painted, it should look just like the stock arm (except the added thumb connections).



The tack welds are visible, these will be fully welded seams once completed.
Roger is welding ALL the locations Kubota welded,
including the hole made just above the bucket to secure the pin sleeve.


Note the 1/4" steel is visible on the sides, this arm is 2 times thicker than stock.
Weight increase wasn't so bad, maybe +20lbs,
I was a little worried as Roger tends to make army tanks out of his projects.
I really appreciate his help.

[dfkrug]

Originally Posted by MacPDaddy

I managed not to get pictures of the actual damage.

Sorry to hear that! Pix would be useful in the TBN "archives" for a record
of what can happen with these bolt-on thumbs.

As for my thumbs....mechanical vs. hydraulic meant different weldments.
Plan carefully...un-welding is not pretty.

The only damage sustained on any of the 6 thumbs I have made resulted
when the user failed to see a pin come halfway out. The thumb has
been bent back and is in service again. Never seen dipper damage.

BTW, I am surprised that your dipper is made of 1/8" steel, as the B21 hoe
I used to have used 3/16" like my current hoe.