ATI grapple design flaw?

   / ATI grapple design flaw? #1  

jedjoe

Silver Member
Joined
Oct 1, 2004
Messages
178
Location
Warren, Connecticut
Tractor
new holland TC 35A 2004
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!
 
   / ATI grapple design flaw? #2  
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
 
   / ATI grapple design flaw?
  • Thread Starter
#3  
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.
 
   / ATI grapple design flaw?
  • Thread Starter
#4  
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.
 

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   / ATI grapple design flaw? #5  
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.
 
   / ATI grapple design flaw? #6  
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.
 
   / ATI grapple design flaw?
  • Thread Starter
#7  
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.
 
   / ATI grapple design flaw?
  • Thread Starter
#8  
here's a photo I have on the grapple before the break. Sorry it is not of the right area of the grapple.
 

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   / ATI grapple design flaw? #9  
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
 
   / ATI grapple design flaw? #10  
jedjoe said:
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.
 
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