hello All, I've recently been wrestling with Caterpillar 304 boom issues, tell me what you guys think about casting welds, pivot pin flange strength, and so on. Back story: At least 10 years ago, before the guys I got this machine from owned it, it was an abused 'company car,', no surprise there. There was clearly an incident involving the shear of the right hand cast flange ear, and it was welded back on, and a reinforcement plate was added to the outside, as people do; I've seen this sort of repair pretty often. They did not work on the left side, the side more complex to reinforce, due to the pin flag needs there. I recently sheared off this side - I swear to dog that I wasn't bashing the bucket laterally, trying to move a parked car out of a red zone, etc. Upon inspection one can see that there was likely an old crack on the left side, behind the stick, maybe from the original incident that broke off the right ear, and possibly they ran a little weld there, but stopped short of really working on the left, who knows, but it was ready to go at any stressful moment... ...water under bridge now on that thought, anyway.. So to the inquiry: 1) Clearly, though these castings on both ends of the boom are not cast iron, there are cast (or forged?) steel, and are welded to the boom box made of plate steel and therefore are perfectly weldable, and their strength especially with added extra 1/2" plates can be restored with proper welding technique. Is this not true? 2) Now that the shop has welded the left ear all up again, adding a reinforcement plate to the left side, which looks good, (though of course the bill makes me shiver), like one would expect, the worn inside bosses where the shims and the stick ride are not square to the pin as one would like. I have to decide whether it's worth the trouble and extra expense to build the bosses back up and have the shop mill them square again - to avoid a .1" worth of slop on both sides of the stick/boom pin and some unhappy bent up shims. In other words, this is the 'make it work to get back to jobs' or pay extra so the machinist looks at it and is filled with pride at doing something pretty (that I will go off and screw up again.) To me, slop on that pin, seems like extra stress on the cast ears, which I will want to watch closely now. What'd ya'll think about all this? Photos: 1) The new break inside 2) The missing ear, obviously 3) The new repair on the left 4) The old right, inside weld(s) TIA - gibbs
When they welded up the ear they should have made it square the machine, we usually mounted it before the final weld. Also need a good welder to make sure the weld doesn't pull the ear one way or another.
If it was mine I wouldnt be doing a crap ton more welding on that casting. I think that would negatively affect its strength. It looks good to me the way it is with those reinforcing plates on both sides. This is a mini 4 ton right? How old is it? I would just run it.
If it breaks again fab up a new end of the boom from all plate steel.
Yeah, I hear you there, as does my wallet. I guess the build up on the boss faces would be somewhat minimal, just enough bead to fatten up about a 10th of an inch, mostly on the outside, to allow mill square to the pin. I think if I said 'You guys shoulda compensated for the shrinkage/cool-down warp when you melted the ear back on." they'd tell me to stuff if. They were using a perfect crack across the flag pin tie-down bolt boss as a guide for the ear's position. They could've pulled that crack open some, and tried to get the ear to stay more inward on cool down, maybe avoid this extra resurface work, but they also followed the pin location in the bores, and it slides in and out well. They also mocked up a surrogate stick bore 'tube' to locate the bores during the repair, clamped the whole thing down at exactly the stick bore dimension. But they warned me it might move out, and it did. I'd guess that half of the non-square issue is just that the bosses are worn - not just a result of the weld-up movement, but from machine abuse. The same shop fixed the stick bottom bore, which was thrashed from jokers slamming the thing on the ground since 2006. The machine is nearly 20 years old, and indeed close to 10,000 lbs. Guys who know more than I, say the machine was already overweight for its power, and then they stuck the heaviest long stick on it, a huge thumb and cylinder from a larger machine - AND a WR adapter and heavy buckets. Anyway, enough with the sob story...!
Have you looked for a used replacement?
Sooner rather than later I would suggest........
I have not seen such a boom available, yet. But I can look into it. 304 was not uncommon, maybe one will see a parts machine somewhere. Sounds like you guys have little faith in the repair.
IMHO there was one chance, and one chance only, of a successful repair of that boom foot and that was when it failed for the first time. Unfortunately whoever attempted the repair blew it big style. Repeated heating cycles from subsequent repairs will have done nothing for the toughness and crack resistance of the steel. It will fail again I think. 270-6449 Boom & Bearing Assy is what to search for in the usual places. This is the PArt Number that was what's fitted to NAD04265 when it was built. BTW please can you post in the Compact Excavators section in future. That's the appropriate location for Lawns & Gardens equipment.
ok then, duly noted.
I think they meant the whole machine...
hmn, well the Boom assy P/N suggests to me a search for it, but I take your point.
I'm good at breaking stuff and welding it. I'd machine up a spacer pipe to fit between the ears, use the flat boss surface to locate them along with the pin bore center and clamp it to dickens! Once you're square, straight and tight, a couple short tack welds on the end and give it a good warming up with a propane weed burner clamped on a stand while you go make lunch. Once you can get the casting pre-heated to start with, vgroove out all that nasty cracked area, the metal is likely stretched and beat to hell and full of oil. Groove one side and add a few good tacks, remove the spacer, groove the inside, reinstall the spacer and tack up the inside, reheat, 250-300f should be enough, can get it into a good position so you can be comfy and start welding, alternating passes on each side until its nice and full, keep the temps nice and warm. A little post heat to heat it all up and then wrap it in a welding blanket for a couple layers then some moving blankets and give it a nice long slow cool off. Then go break it again someplace else
I was assuming the rest of the machine was in half-reasonable shape......
Now now! just because it takes all week to move 1100 yards versus ten scoops ...
Well, I confess I didn't study the forum categories, my mistake. I will say in defense of the mini-things, though I might be happy to have a steel-tracked 308 up on my precarious 100 year-old dirt logging roads, a big scoop will not fit, either on the 8' wide trails, between the dense trees, etc., and when we had a 321 out there, several ops said things like: "I'm not getting that close to edge there in this thing, go get the mini."
It’s nothing to do with that, although with my sense of humour it’s always possible. Did you ever read something and think “that exact same thing has come up before. No point in reinventing the wheel - the same answer will work.……” Then you go looking for where it ought to be (as in the appropriate section of the forum) and can’t find it because it was posted somewhere else. The search function is not the best so looking for it is often a lottery. Hence my request to the OP. FYI. The forum admins are very helpful when it comes to moving threads. All anyone has to do is click the Report button in the bottom LH corner of a post and send them a message.
One thing I have learned after watching youtube channels like ICWeld or On Fire Welding, is those professionals are not afraid to cut and grind the **** out of these cracks and failures and put in a tonne of weld. Weld in new plates, fabricate stuff, etc. Watch a fair few of the videos on those two channels and you will soon get the gist of how to fix things properly. I was one of the all too common barely gouge it out and lay half a rod over it to fix a crack crowd until I saw those two in action. Now I am a convert.
And that’s the “one chance” I was referring to earlier. Screw it up the first time by not gouging deep enough and trying to butter over the top and you have effectively scuppered all subsequent attempts at repair.
It can't be a crack if there isn't any metal there, then its just 3d metal printing
Looks like a simple repair to me. But we loggers break a lot more stuff than dirt movers for the most part. But when I do get started on a repair like that, once its all aligned I would weld brace pieces across the gap down at the end to maintain alignment until done and cool. Then simply cut them back off. I have made many repairs like that on much bigger machines with great results.
I appreciate all youse comments, thank you. Forgive me the long summary of the job, I think much of your advice has been taken. It does seem clear, and would be my initial assumption, that repairs be done properly. If it wasn't clear, the current break, on the left ear which was either not affected by whatever event broke the right ear some 15 years ago or not, in other words, was old and unaddressed or new - the current welding did not 're-enter' any old welds. I take the points summed up by "one-shot at it." The right ear repair from 2008 or whatever has not broken down and has survived at least 10 years of continued pounding, and I as may have mentioned, ops then did not 'baby' the machine in any way, quite the contrary. The current shop, which has done several jobs for me, has a 'go the full distance' attitude about machine work. I think their effort on this weld up reflects our collective comments here; they fabricated temporary alignment members, dug in to get solid weld in the break area, cooled the work properly, added the substantial top plate, etc. I do now have the complication that due to both repairs and general wear from 20 years of service, the bosses are not square to the pin. Again, to set up the repair the welder had 3 things to align, the outside position of the ear by the crack through the flag tie-down boss, the slip fit of the pin and the parallel on the casting ears. Unfortunately, the square to the pin and the ears lost out. They'll now build up the wear and mill it square again, thanks to my credit card. I've told them not to reopen up any existing welds; they did not suggest that anyway. None of this keeps me from looking for a salvage boom, if one can be found, swapping machines, or fabricating a plate steel front end if it comes to that. Anyway, we'll all be happy to know that "The fun never stops." and "There's always one headache or another." and "It's best to stay busy." and so on...!