Nige
Senior Member
Bob, usually the problem will not be in a casting. The box part of the boom has internal webs or stiffeners in it to stregthen the box away from the areas where the castings provide natural reinforcement to the structure. It is usually the welds between the stiffeners and the outside plates of the "box" of the boom that crack. When you cut a hole open it's generally obvious what's wrong as soon as you stick your head (and a light) in there. There will be one or more cracks in internal webs - fail to fix those and your repair on the outside hasn't got a snowball's chance in Hell of lasting.
I can only speak for Cat here but if there is a known issue in a boom there will will generally be a repair procedure document known as a Special Instruction that tells you step by step how to do the repair. While that document may only apply to a certain machine model there will often be some really good titbits of information in it regarding procedures that are transferrable across the whole models range - excavators as an example. As an example from my job site we had 336D excavators where the stick cracked on each one, every time in the same place. Cat must have known about it because there was a Special Instruction available that as a first step required the repairer to cut a rectangular hole in a specific place. One the plate was removed there was access to 3 internal stiffeners, all of which had cracked the welds between them and the side plate. Repair the stiffener-to-side-plate welds, pop the cut piece of plate back in the hole, weld it up, and the put a external stiffener plate over it (where do you hink I got the sketches I posted a few pages back?) and Bob's your fathers brother.
I can only speak for Cat here but if there is a known issue in a boom there will will generally be a repair procedure document known as a Special Instruction that tells you step by step how to do the repair. While that document may only apply to a certain machine model there will often be some really good titbits of information in it regarding procedures that are transferrable across the whole models range - excavators as an example. As an example from my job site we had 336D excavators where the stick cracked on each one, every time in the same place. Cat must have known about it because there was a Special Instruction available that as a first step required the repairer to cut a rectangular hole in a specific place. One the plate was removed there was access to 3 internal stiffeners, all of which had cracked the welds between them and the side plate. Repair the stiffener-to-side-plate welds, pop the cut piece of plate back in the hole, weld it up, and the put a external stiffener plate over it (where do you hink I got the sketches I posted a few pages back?) and Bob's your fathers brother.