Hydraulic thumb

[Shimmy1]

I've installed a number of thumbs on excavators going back to 1979. I hadn't seen the thumb pin mounted on a boss welded to the stick before. I'm sure it works but would be a little leery of its long term life. Hopefully you guys can tell me you haven't had to weld a stick back together after a couple of years of use.

The key is to have one that has a plate that holds the cylinder mount and the thumb mount. That way, the forces applied by the cylinder are transmitted more so lengthwise on the stick rather than pushing on the tube. I've seen pics of the cylinder mount "beer-canning" the stick. Mine uses a ½" plate to hold the pin bosses, and the thumb boss is almost fully over the bucket hinge pin casting on the end of the stick. I use mine as hard as I would use a pin-mounted thumb, have been for two years. Like has been said up-thread, a pin mounted thumb is the best, but my work requires me to take my thumb on and off so often that it just doesn't work for me. I can put it on or take it off in 20 min, quicker if I have another guy to help. BTW, John C, what is your opinion of the thumb that I built?

 

[John C.]

I think what you are describing is somewhat like the machine posted above. I like the 1/2" plate idea real well and don't see any problems with it. We do have contractors in our area that work with underground utilities and the thumb just gets in the way. I think they would be receptive to what you have done so they could work two kinds of projects with one machine. Do you put the pin boss back just enough that the bucket top edge clears?

 

[Shimmy1]

I think what you are describing is somewhat like the machine posted above. I like the 1/2" plate idea real well and don't see any problems with it. We do have contractors in our area that work with underground utilities and the thumb just gets in the way. I think they would be receptive to what you have done so they could work two kinds of projects with one machine. Do you put the pin boss back just enough that the bucket top edge clears?

Exactly. The coupler hook is what actually interferes with the pin boss. When we welded the plate on, we had the coupler curled all the way in, and set the pin boss about ¾" from the hook on the coupler. I thought about putting it closer, but figured I better leave some gap to allow for wear in the pins and bushings. I would hope I never let the wear get that out of hand, but maybe the next guy might.