Thumb Kubota BH75 Damaged by bolt-on Thumb

MacPDaddy · Sep 1, 2008

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 · Sep 1, 2008

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 · Sep 1, 2008

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 · Sep 5, 2008

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 · Sep 6, 2008

john_bud said:
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 · Sep 8, 2008

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 · Sep 8, 2008

john_bud said:
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 · Sep 8, 2008

dfkrug said:
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 · Sep 8, 2008

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 · Sep 8, 2008

MacPDaddy said:
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.

MacPDaddy · Sep 8, 2008

dfkrug said:
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.

I was also pretty suprised how thin it was. I asked Roger if he could get a short cross section so I can get a picture of the original stock as well. He may, but no promises at this point as they may have sent out scrap already.

Actually it looked like the arm had a slight bend between the 2 bucket pins, I may assume that 1/8" may be slightly on the thin side for digging alone. During my visit to the dealer this past weekend, it did seem like the thickness in the hoes had been increased, maybe 3/16" is now used. I appreciate your input, pretty new to thumbs.

dfkrug · Sep 9, 2008

MacPDaddy said:
Actually it looked like the arm had a slight bend between the 2 bucket pins, I may assume that 1/8" may be slightly on the thin side for digging alone.

Your pix in post #6 above do seem to show some curvature in the dipper.
Amazing. To actually get some bending BETWEEN the pin holes in the dipper
is more amazing. Let this be a warning to anyone with a Kub BH75 not to
use a bolt-on thumb.

Your replacement dipper stick looks good.

AKfish · Sep 9, 2008

Somethin' to consider for everyone using a bolt-on thumb.. not only BH75 owners - IMO. And this forum is a great resource for all of us to benefit from the experience of one another.

Ol' Roger is a good hand - he done real good - the repair looks like OEM.

Looking at your pics; it appears that the thumb will only fit down low on the dipper - close to the pivot pin on the bucket. Or maybe that's just the way the pic looks..? If you could move the thumb up higher on the dipper; the compression forces from the bucket against the thumb would not be at such an abrupt angle to the dipper stick; I'd think.

The inside plate (between the side walls) on the dipperstick on my old JD 8A hoe was thin, too. The side walls were heavier plate (1/4") as I recall; but the inside plate was all bent up and rippled from rocks, trees, etc. being forced against it by the bucket during normal use.

When I welded the thumb on, I used 3/8" plate for the upper and lower pivot points on the thumb and that ended problems with rippling...

AKfish

MacPDaddy · Sep 11, 2008

AKfish said:
Looking at your pics; it appears that the thumb will only fit down low on the dipper - close to the pivot pin on the bucket. Or maybe that's just the way the pic looks..? If you could move the thumb up higher on the dipper; the compression forces from the bucket against the thumb would not be at such an abrupt angle to the dipper stick; I'd think.
AKfish

Yes it will only fit low on the arm, you run into hitting the cylinder if you place it any higher.

MacPDaddy · Sep 19, 2008

I have the finished arm back tonight.

I also got a cross section of the original arm which I will post pictures of, it is 1/8" steel all the way around.
Tomorrow is paint day, I don't know if I'll get to install it. I'll take pictures and post them this weekend.
We did install thumb attachment locations, the thumb construction will happen later.

MacPDaddy · Sep 20, 2008

The arm is ready to paint.
The only Kubota parts are the 2 plates at the top, and the 3 pin sleeves.
Notice the installed thumb support and the third sleeve for the thumb mount.
We will design the thumb once we have it back together.

The craftsmanship that Roger put into his work always amazes me.

A slice of the original BH75 Kubota dipper arm shows the 1/8" steel construction.
In my opinion, this is a little light duty for the arm. I guess it works as long as you don't get too overzealous (or stupid as was my case).
As I said earlier, it looks like the arm had bent BETWEEN the 2 bucket pins, and I don't think that was the thumb's fault.

Unobstructed view of the factory Kubota BH75 dipper arm section.

Compare the old arm section to the new heavy duty arm.
Surprising that the overall weight increase was only about 20 lbs.

I'm really happy with the result, the 1/4 steel is visible on the end.
Roger duplicated every factory weld, even the sleeve welds visible here in the center of the end piece.

Primed....

and painted, ready to install tomorrow.

irvingj · Sep 21, 2008

Wow, that looks beautiful!! I'm also planning to add a thumb, probably Bro-Tek, to my M-F GC2310. Anyone out there have experience with this set-up? Does the 2310 have issues with the use of a thumb?

MacPDaddy · Oct 7, 2008

ALMOST DONE!!
The Thumb arrived today (Roger and I fit it last Friday so I know it's good).
The only thing left is to get it painted and installed.
The thumb is made of 1/2" thick Hardox 400 steel, the same material often used for buckets or dump truck beds on large equipment.
I am using Kubota Orange on the support strut and ROPS Grey on the thumb itself.