Howdy all! In lots of Google searching and YouTube watching, I am amazed I couldn't find a similar situation that I find on my 2000 John Deere 200LC. It has very serious, matching cracks on the sides of its CWS hydraulic thumb. I bought it a few years ago to stump out my 20 acres and for general Farmer Joe type work around the homestead. None of the pictures can quite capture it, but the cracks stop at a slight dimple, about an inch in diameter, on the inside and outside of both sides of the thumb. Almost like a hydraulic grapple handled the molten casting before it hardened up. It is quite obvious why it WOULD crack there. It is right where the sides of 1" plate become the 2 foot wide thumb as a whole. Obviously; 1) I need to completely grind out the crack. Emphasis on (completely). 2) Drill out the "end" of the crack, perhaps an inch past where it appears to end. 3) Preheat before repair welding, one pass on each side, back and forth till filled. 4) Protect all ram surfaces and auto grease/hydraulic lines from heat and welding splatter. I think a backing plate on the inside surfaces used as a floor for filling in the completely ground out crack is in order. I'm thinking roughly a 3x6 incher. Filled pass by pass, slowly. Topped with an outside plate of same size and perhaps a strap where the crack originated, (1"x6"). All plates out of 1/2" plate stock. I just got one of the new Everlast MTS252STI's, very awesome unit! 250 amp mig, but only 200 amp stick output. Questions; 1) Is all the plating overkill? 2) 6010/8010 root pass? Followed by 7018/8018.......11018? Flux core E71T-GS with gas (dual shielded) MIG? 3) Rod size? I have access to my neighbors 350 amp transformer stick welder and some old 7/32 7018's on my shelf (that will need some bake time). After pressure washing looks like the 80mm stiffener bushing on one side of my Hendrix has busted its weld as well. Grind out and re-7018? Thank you for your input!
Your on the right track. I usually air-arc cracks like that much faster but, I have the equipment to run one. If you can get a good solid full penetration weld without any undercut it would be fine just welded up. You have to keep in mind it has lasted 15 years or so. If repaired properly it will last a long time without fish plates. You should also check the hydraulic pressure to the thump cylinder. It should be slightly lower than the bucket cylinder pressure to help avoid an incident like that. By the way throw that xx10 wire in the bottom of the next ditch that you dig. It has no place on any equipment repair in my opinion.
I can't speak to the welding repair as Theweldor has, but he is dead on with his suggestion to check that thumb pressure. As a rule , I've never seen one with relief set higher than 2500. The idea is , you want the bucket to overpower the thumb. The thumb cylinder must yield to the bucket or you end up with what you have. Usually, you would have cylinder failure prior to structural damage.
Cylinder pressure may be an issue. I've had to rebuild the thumb cylinder twice in the last 2 years. While I've got the welder out I need to scratch my head a lil and figure out a stop for the thumb so it's not possible to hyperextend the cylinder. It seems to be subordinate to the bucket, but not by much. Judging by how beat up the thumb is, I'm guessing it is a fairly mild steel and 7018 would suffice. Not sure its hyper critical, but I'm a bit of a perfectionist. My questions stem from the 8,649,413 different opinions that YouTube videos seem to offer on the subject. Best to listen to folks like I find here, that have been there/done that. Thank you!
Those thumbs are not built out of anything exotic. If you are going to grind out the crack you will put enough heat in it that you won't need to preheat it. The crack is probably going to extend 1 to 1 1/2" beyond what you can see. Odds are good it has been on that machine since new it is allowed to look beat up.
That looks like pretty thick steel so preheating would never be a bad idea especially if you're limited in the size of electrodes you can use. It looks like the crack(s) may have started at the edge of a weld possibly from no preheat when the thumb was built. Slight undercut or too convex of weld could cause a notch effect as well. I would try to do the welding in the flat position. You don't need a backing plate but do the first 2 or 3 passes from the harder to get at side and then grind out the "root" pass into good solid weld metal from the easy to get at side. I ripped the top mounting plate for the swing on backhoe off. The crack started down the center line of a grease fitting and followed the edge of the weld on the bushing all the way around. This was on a Cat hoe but I believe what someone suggested that these things are slapped together and not much thought to preheat or welding procedures goes into them. On bigger stuff maybe but the edge of a weld can be the perfect place for a crack to start. Don't leave weld craters at the ends. Weld from each end and have the craters in the middle. I wouldn't use anything other than stick electrodes. You want to put heat in but not too much heat too fast like dual-shield flux-core might do. 5/32 and maybe 3/16 7018 or even 8018C3 with 1% nickel for more toughness would be my choice of electrodes but you could always call CWS and ask what material they use. Mig or E71T-GS no way. E71T-GS is a self shielded flux-core wire that doesn't meet any specs. It might be OK for ornamental iron work. I refer to the GS as generally ****** for anything you need to be strong. Peening the welds with a dull chipping hammer between passes is also a good idea. Let it slow cool and wrap with a non flammable blanket if you have one. Lastly, if you don't think you have enough experience nothing wrong with getting a more experienced welder to help you. You want it fixed right the 1st time.
Thank you for all the advice, gentlemen! I picked up some 5/32 7018's on the way home tonight. I wish my 250A Lincoln gen welder wasn't burning more oil than fuel right about now! I think I am aways past "farmer welding" , (blobs of worm holed molten metal piled thicker than the base material), but I know a "stack of dimes" bead by no means makes me any sort of professional craftsman. One of these days I hope to have the time to learn more of the science behind it. Still won't replace day in/day out occupational experience though, hence my digression to the knowledge base of you gentlemen! Thanks again!
That's a common occurrence on thumbs. I notice the pivot pin flag isn't anchored to the quick coupler so now the bucket can rotate on the pin. Generally you want the pin to be locked to the bucket or in the case of the photo to the quick coupler. The other issue that I commonly see with this brand of attachments is that the thumb impinges on the coupler before the tines on the thumb contact the cutting edge of the bucket. Another issue is that most of the manufacturers started using T1 or HY80 steel for the sides of the thumb and AR plate for the tines. As I recall this manufacturer used mild steel for the body of the thumb. For a fix most people just try to bend the thumb back to try to close the crack some and weld it as described above. I usually see a 3/8" minimum fish plate installed over the top of the crack running about a foot each way as possible for the shape of the thumb. Sometimes that fish plate will interfere with the sides of some buckets so keep that in mind.
The heat from welding and then contracting will likely pull the crack closed. The weld has to be able to move or it puts the repaired area into more stress. Peening between passes along with preheating and even post heating helps relief built up stress in the steel.
Experienced welders worth a flip would use a run-on-tab and oxy-ac torch to scarf out the cracked area. Scarfing (Victor #2 tip) pre-heats the surrounding steel plate adequately before immediately welding the crack. 5/32" 7018 @ 180-185amps preferred; that most lesser experienced welders would consider to 'hot' and use 160-165amps. Mild-steel there won't be underbead cracking issues if the crack is opened up to a 'double 30 deg V' or U for one side weld repairs. I use GMA MIG 'dual-shield'-'outer-shield' .045-052" for all field weld repairs because the flux will self-peel or require light pneumatic peening eliminating between pass grinding. Grinding sends employees to visit the medical professionals to dig out embedded particles in the eyes or worse. High strength HY-80, T1 (A514) AR400, WeldOx, HardOx etc requires using stringer beads (per codes, per manufactures' welding instructions) to prevent weakening the base plate(s); caused by using wider beads that spread the heat effected zone. Design the fish plates with space for a 75% fillet weld height @ edges.
I went into my archives and found some photos of repairs and some showing common damage seen on thumbs. In my experience CWS is in British Columbia, Canada and has been working in the Northwest United States market for around ten to fifteen years. The first photo shows how the welder designed the reinforcement to go around the relief hole. The second photo shows a factory design that ties the pin area to the area with the most stress.
The next photo shows a poorly designed repair but apparently it has held for years with no new cracking. It looks bad but apparently it worked. Also note the main pin flag is tied to the thumb now instead of the bucket. The bucket pivot joint was very sloppy.
The next photo shows the other place that should be checked for cracks. Not that this type of thumb is cross plated and the twisting action applied to the thumb legs has caused the cracking at the plate to leg joint. If you look close you can see the fish plate that was a factory install.
This last photo shows what happens when there are no grease fittings installed on the thumb bosses. Some manufacturer's didn't put them in. The maker reinforced the strain area but didn't install grease fittings?