ATI grapple design flaw?

[jedjoe]

Anyone out there have a metal failure on your ATI grapple? I have the model GK-4866, and have gotten good use out of it since I bought it in fall '04. The overall strength of the unit is good, but the joint that connects the grapple claw to the hydraulic cylinder has failed. The metal just tore away! I priced a new claw at about $400 with freight from ATI via my dealer.

If anyone else has had a similar problem, please let me know!

 

[texbaylea]

I have the same grapple and have not notice any signs of failure. Is it a weld that failed? I would suggest that you find a welding shop and let them advise you on what is possible in repairing the present claw assembly. This should be more economical than buying a new claw assembly.

Vernon

 

[jedjoe]

Thanks, Vern.

I'll take a picture and post it. The metal actually tore. I had it mended a year ago, and then a new tear occurred.

 

[jedjoe]

Here's the photos. I took the claw off the tractor for either repair or replacement. You can see that the weak link mechanically is the connection between the claw and the hydraulic cylinder. Last year, the metal arm cracked. My welder added the three plates. Now, the metal has torn above and below the repair.

 

[mboulais]

Jedjoe,

Hi,

As a mechanical engineer I might be able to give some insight / advice. It is hard to be sure without looking at it in person, but my first guess is over loading. My second would be a geometry problem.

Is there rust in some of the break and not in rest (I'm looking for signs of crack progression over time)?

Are there curved lines in the surface of the broken metal (I'm looking for overload vs fatigue)?

What diameter cylinder?

How high is the system hydraulic pressure?

Do you have any pre-failure opened and closed photos(looking for geometry/design problem)?
Judging by you're avatar, you have at least one open photo.

 

[mboulais]

I went to thier website.

Is it bolt on? I didn't find an open picture, but it looks like the geometry of the design is ok (not trying to swing through more than 89 degrees of arc).

If it gets to 90 degrees 100% of cylinder force goes into the pivot points and cylinder mounts instead of being used constructively by creating motion.


In the closed position, did the grapple tips hit the bucket before running out of stroke on the cylinder? I would recommend it not touch.

 

[jedjoe]

Marcel,

Thanks for the excellent feedback. To answer some of your questions. It is a bolt on design. In the open position, less than 90 degrees of arc. In the closed position, the grapple claw does not touch the bucket edge. If you look at the last photograph in the previous post (the one with four photos), you will see some rust in the crack, confirming your suspicion that the metal cracked over time.

 

[jedjoe]

here's a photo I have on the grapple before the break. Sorry it is not of the right area of the grapple.

 

[texbaylea]

jedjoe

I looked at the last picture and noticed the ripples in the webs between the tines. Mine has not bent up that way. The grapple must have bit down hard on something that didn't give. My hydraulic cyclinder runs out of travel just before the claw tips hit the bucket teeth so I can not over stress the unit while closing on an empty bucket. I also am careful not to apply too much force closing on the load in the bucket.

Vernon

 

[mboulais]

Marcel,

Thanks for the excellent feedback. To answer some of your questions. It is a bolt on design. In the open position, less than 90 degrees of arc. In the closed position, the grapple claw does not touch the bucket edge. If you look at the last photograph in the previous post (the one with four photos), you will see some rust in the crack, confirming your suspicion that the metal cracked over time.

I wouldn't try any more fish plate repairs. Cut away the whole cylinder mount and start over. I will post a sketch of a possible fix.

 

[mboulais]

I would guess that the cylinder mount is seeing more load than it can handle, but not gross overloading, causing fatigue failure. I think the old cylinder mount needs to be completely replaced. When you do that you need to "beef up" the surrounding area to aviod moving the problem to the next weak link. These are quick sketches. Old stuff needs to be cut off after carefull measurements are taken on hole location for the cylinder rod end. Add 3/8" plate to the existing thinner plate in the corner of the jaw. Add 1/2" or 5/8" plate at the right spacing for the cylinder rod end (probably 2.5 - 3" inside). drill the new holes in the new plates for the cylinder rod pin. A good quality hole saw will make a clean enough hole. additional gussets back the jaw behind the new plate wouldn't hurt either. If you need more help let me know. Grapplerepair1 is a back view of the grapple, grapplerepair2 is the side crossection.

 

[jedjoe]

marcel, thanks! I have to say, these discussion forums are the best! I'll run your description and rough sketches by my welder, and see if he is up for it. Given that a new claw will have the same design characteristics as my present broken one, I figure its worth it to try your suggestion.

 

[Hammy]

Jedjoe,

I have a new ATI grapple that just failed as yours did. I posted some pictures for you to compare with. I'm going to see if I can get my money back as I've only used it for about 2 hours.

In one of the pictures it looks like there is a bend in the cross tube but there isn't. It just looks that way in the photograph.

Have you come up with a fix yet?

Craig