I recently picked up a EX120 and it has a manual thumb installed. I noticed when we looked at it that the teeth of the thumb did not align very well with the bucket. We also knew that the bucket pin had a bit of wear, so I assumed that was why. Once I received the machine and upon closer inspection, I realized that one side of the thumb plate down near the pin has a bow in it, therefore the thumb pin does not sit square and flush on the stick. It has been welded around this bow so it is secure, just not straight. I eventually want to rebuild this thumb and redesign it to pivot off the bucket pin and also change it to hydraulic. What is the best way tot go about removing this thumb mount plate from the stick without causing issues that would weaken the stick....? Pics will follow later, I just realized that I had not taken pics up close of this issue....
If it was still doing it's job reasonably well without cracks around the base, I'd first get try and straighten it it with the help of some heat, a BFH, and/or a long bar that fit in the pin hole. To get the plate off, I either reach for gas axe or the air arc and gouge the welds out. If you're careful not to get into the base metal, it shouldn't cause too much of a stress riser. The new plate could be larger than the old one, covering the old area and putting the new welds out on fresh metal. Greyson
I could do either, I have a torch and I can burn the gouge rods in my Lincoln. I will not do doing this for several months at least. But when I convert this to a hydraulic thumb, I want it as correct as it can be. To straighten it, weld would have to be cut, so either the plate was already bend when it was put on, or it bent afterwards, maybe due to some weak welds and the bucket broke the welds and bowed the plate and it was re-welded in that position. So to fix or replace it welds will have to be cut. I guess I would look at this as the plate being the most sacrificial part and if it meant loosing material on the plate and having to grind the rest off the stick, then so be it. I just want to be sure that I don't weaken the stick when I do this. I machine wiht a broke stick is no good to anyone.
Some pics would help if you could post some. Does your machine have the necessary hydraulics for a thumb?
I did not get up there for pictures yesterday. Will be there tonight... I will get pictures. Yes, the machine has an open valve on the hydraulics and it is plumbed to the pilot controls. I will have to plumb from the Hydraulic block to the thumb cylinder and install an electric solenoid to control the pilot as I want the thumb control to be a switch on the right joystick controlled by my right hand thumb.
Pics attached. You can see the bend in the plate on the stick. Might not look like much, but the thumb teeth are no longer aligned with the bucket teeth. Don't have a pic of that yet.
Good morning. Just a reminder, that when you eventually switch to your hydraulic thumb. To remember to make sure it has a circuit relief installed and set low enough. That bucket will be able to push thumb back without bending the thumbs cylinder rod. Love hydraulic thumbs. Good luck.
i have the same mechanical thumb, and had the same issue. I cut and removed only the lower 14" or so of the plate, removed the square tube from the plate, and replaced the plate with something thicker, and reinforced the snot out of it. here's a few pics (please excuse my not-so-pretty welds)