Cat 305CR with a crack in a weld for the boom cylinder attachment point. The crack is only on one side of the boom and only affects the outside weld on that side. Any reason to do more than grind/scarf out the weld and re-weld with 7018? Thanks!
Broken boom Any tips on how to fix this? HeavyEquipmentForums and: HeavyEquipmentForums You can do it as easy or as hard as you want. That's suspiciously good paint, was it previously welded over, and repainted to sell?
It has definitely been painted. I looked closer at the welds on both sides. The welds on the inside of the plates look like a large single stringer that is very uniform in appearance. The welds on the outside of the plates look like 3 passes and don’t look nearly as uniform, so it’s possible they have been welded before. I used the excavator on my farm, so it only gets used a few hundred hours a year, at most.
It certainly looks as though it has been welded before and painted over. That weld in your photos does not appear to be factory. My question would be how good are you at welding overhead.? On a machine as small as a 305 you might consider removing the boom and turning it upside down so that the weld can be done downhand. According to the book the bare boom only weighs 170kg. I know it's a lot of disassembly but do you want to repair it once and do it right or run a bigger risk of it re-cracking.? Also it looks to me as though on the RH side of the photos the crack runs out of the weld and into the bottom plate of the boom. That might be another good reason to pull the boom off to make the repairs because when you scarf it out you might just be opening a can of worms.
When you do weld it, preheat and postheat(stress relieve) would be a good idea and make sure when you prep the area, you grind enough of the crack and a bit past the ends to make sure all the crack has been removed
Beating the bejasus out of each weld pass with a needle gun to stress-relieve immediately after laying it down would also be a good idea.
Seeing that very long crack leads me to suspect a bad material.
Seeing the crack disappear from the weld into the parent plate is screaming "look inside the structure" to me. I'll bet that inside that boom somewhere in the area of the cylinder attachment point are one or more transverse baffle plates with at least one dodgy ex-factory weld between them. A crack in a baffle plate weld allows the boom structure to flex more than it was designed to do and, hey presto, the result is external cracking. I'll also bet that the crack started from the RH side as you look at it in the photo and is advancing to the left.
If that is the case, looks like shoving down was the overload, not lifting up. Suspect a hammer was fitted on the machine ?
The problem with dodgy welds in the internal baffles of a boom or a stick is that the stresses from NORMAL operation will lead to cracking. It's not necessary to have a work tool such as a hammer installed although I don't rule it out.
I did run a hammer for about 25 hours. I figured it might be related. I’ll grind it out and see where it leads…
The pictures don’t show it well, but it appears the crack is confined to the weld zone and doesn’t extend into the pare material.
When you finish grinding it out please post some photos before you start welding.