For a SK 250 Kobelco. It already has a plate under the stick. Actually had a thumb at one time but was removed before I got it. Fixin to put a new Pemberton thumb on it. Instructions say weld all the ag around but leave a 2 1/2 gap on the end and weld out to small pigtails for stress relief. I've seen thumbs that were welded like 4" then a 2" gap then 4" etc all the way around. Also they suggest welding with E7018 stick. I was considering weldin with wire. I can do either one. Just looking for opinions. Thanks for any input
Most I have seen are all welded on sides and not the ends as it's no good to weld perpendicular to the stick. I don't see a problem welding with wire as long as you get a good penetration.
Why not weld perpendicular ? Im not a welder but a welder I was just talking to said he had welded on hundreds of thumbs all the way around and never had one come off but recently a customer said not to weld the top or bottom of the thumb mount plate ? What the reasoning ?
I think it would be stress relief. On the 7018's try to weld with a new package if you don't have a Rod oven.
Is your thumb a hydraulic or stiff leg type?
It can crack along the the heat affected zone.
It's a stiff leg thumb.
Do the gap and pigtails, lessens the chance of cracking across the plate a lot. If you're good with wire use it, if in doubt use 7018, can't go wrong there usually. Preheat some before welding either way.
Since you already have a plate between the thumb and the stick welding the ends shouldn't be a big issue, it's important to not weld the ends when your mounting the thumb directly to the arm since the arm plate will flex and cause cracking at the ends. I would use wire if it were available, but I wouldn't skip weld the sides. A continuous weld would be your best bet.
Are the ends of the base plates for the thumb and stiff leg cut in a V pattern? I've seen them both ways with the V cut into the center of he mounting plate and with V on the ends of the mounting plates. If the plate has a male V then weld solid to just short of the ends on each side and then whale tail off the ends. If you have the female V cuts then start your weld about a half inch or more from the inside ends and finish them like the male ends. Weld the outside all the way. If the ends of the plates are cut off straight then don't weld the ends at all. The issue with welding perpendicular to the length of the stick is that the load on the stick is taken up along the whole length of the stick. It flexes against that length. When you weld across the stick you interrupt the load moment effectively shortening the distance over which the load is taken up. It's probably not a big deal for tube clamps and such along the top of the boom. On the bottom of the stick though it will crack for sure sometime during its life time.
I appreciate all the suggestions
Should I disconnect the battery before welding on this machine? Don't want to zap the computer. Not sue if the key being off if it takes it out if the circuit
I would disconnect rather be safe than sorry man. Doesn't take a lot of time or money to unhook and hookup myths batteries
^^^Also keep the ground clamp as close as possible to the weld.