Kubota backhoe dipperstick repair

[nkdmrt]

I bought a year 2000 L35 used late last fall. I drew up the parts for a mechanical thumb, and they are being cut out on a CNC plasma. Then I will weld up the thumb and install it.
The problem is that the inside (operator-facing) flat surface on the dipperstick where the thumb base will mount has a bulge in it. The bulge is in the area between the the pins for the bucket linkage. Apparently the previous owner really stressed this thing at some point, but it was likely the only time because the whole machine is in great shape.



I talked to the dealer and what they would do is cut out the bulged area and replace with a new piece of plate. Which is what I thought they would say. They have never done this repair before. They did not know if the steel was an alloy steel or just mild steel.

I definately will not spend the $1,000 bucks for a new dipperstick.

What do you guys think?

Thanks,
Nick

[hankj]

Assuming your thumb base is going to just be a piece of plate welded at right angle to the dipper, what I think I'd do is profile the base of the thumb for the bulge with a plasma cutter or an O/A torch and just weld it up. The worst thing that can happen is the thumb weld will fail, I'm thinkin.

A thumb really doesn't take much pressure in use; it just holds wired shaped stuff in the hoe bucket.

That certainly is an unusual failure. My baby tractor's (B7800) hydraulics would not be able to put that kind of a hurt on the dipper!

Hank

[lanceman73]

Thumb options

Why don't you make the thumb mount as wide as the stick? That way you can weld it to the sides, which is the strongest part.

[nkdmrt]

Hank & Lance;
Thanks for the replies. From all I've read at thumb mfr's websites, they all seem to concur that the base plate of the thumb should set on the flat inside surface between the welds. Then it is essentially welded to the existing welds/sides of the stick. But only welded the 2 sides parallel to the length of the stick and never across the short width of the stick.

I was shocked that the hoe had that muck force. But the L35's are very strong for their size. So they tell me.

The gouge depth to fit over the bulge would have to be around 3/8" at the max, but it is right where the main pin of the thumb will be.

I think it will work to cut the bulge out w/ a wheel (minimize the heat), weld in the patch. Any suggestions for the patch material?

Thanks,
Nick

[J hall]

I would cut it out and replace it with mild steel.

[nkdmrt]

Thanks Jeff & Ironhead.
That's what I was thinking and hoping to hear. I will likely Tig it and grind the welds flush. Then proceed to attach the thumb base plate.

Will keep you all posted as this progresses.

I apologize for the spelling in my posts. Not much for typing.

Nick

[84ZMike]

I'd check for cracks as it could have been water got into it and froze.... I have seen ice do lots of damage to steel even down here were 30deg. is cold

[hogan]

I have inspected many of these. Typically it is CJP welded ( open root or ceramic backing ), back gouge root, welded out, ground flush, and then ultrasonically tested.

[nkdmrt]

Update

Well I chose to try to contour the baseplate that mounts to the dipperstick over the bulge. You can see the contour templates I made in Contouring pic 008. Transverse templates every inch for six inches and one longitudinal template along the centerline. Same technique as what one would do for carving an arch for a violin plate or archtop guitar. Once close to the templates I would spray some paint on the bulge, set the plate on it and whittle the high spots down until the contact all over.
Once the baseplate is welded solid to the diperstick, them I'll finish welding the baseplate assembly itself. Now it is just tacked to minimize distortion...

[c wagner]

Looks good, almost to good to use!!!

[nkdmrt]

Update

Here are a couple pics of the installed thumb:
Thanks for your comments and advice, as always.
Nick

[Telstar2112]

Nkdmrt, nice job! I have the same machine, L35, and am looking to weld on a thumb. I don't have the issues you did with the bulge so it should be much easier. I have a few questions if you don't mind me asking;

Did you ever find out what type of steel the L35 dipper stick is made out of?

The hydraulic thumb I bought has a full length 1/2" thick nearly 3" wide mounting plate with 1/4" chamfers along the back edges to clear the welds inside the dipperstick. I did not fit it up in there yet but it should fit nice and I should be able to weld to the protruding 1/4" side plates.

Question is, is it possible to weld this up using a Millermatic 211 (running on 220v)?

I know the mounting plate is 1/2" which is beyond this welding machine but figure with the big 1/4" chamfers along the back edge, and I can add a chamfer along the front edge, and since it is tucked in there nice along the 1/4" side plates that I should be all right. There is also so much weld length that I am thinking that even I don't get full penetration it should still hold the load.

Any advise is greatly appreciated. Settings, rod, multiple passes, etc? I have standard 75/25 gas, .035 wire, as well as some .045 flux core if there is any benefit to using that.

thanks,
Steve.

[Portable Welder]

We always weld the plate that mounts on the dipper all the way around, otherwise it gets moisture inside and starts rusting, So yes you don't want to weld across the boom that's why they are diamond at the ends so your welding diagonally.

[aametalmaster]

Question is, is it possible to weld this up using a Millermatic 211 (running on 220v)?

I know the mounting plate is 1/2" which is beyond this welding machine

Any advise is greatly appreciated. Settings, rod, multiple passes, etc? I have standard 75/25 gas, .035 wire, as well as some .045 flux core if there is any benefit to using that.

thanks,
Steve.

I don't know how your duty cycle on your MM211 will hold up but i have done jobs like that with my MM185 and .035 gas flux core wire. I welded some thick plate on my neighbors loader with no problems...Bob

[Tryagn5]

Water....

We always weld the plate that mounts on the dipper all the way around, otherwise it gets moisture inside and starts rusting, So yes you don't want to weld across the boom that's why they are diamond at the ends so your welding diagonally.

Water is getting inside the dipper, that's why it is bowed out. Also a sludge hammer would have straighten that right up. The baseplate is not very thick, I would be sure the dipper does not freeze again or it will bend it on the top, which is not good.