Built a pin grabber manual QC for Komatsu PC120 with hydraulic thumb. First mounted thumb at the bucket. The thumb moved when the bucket moved but greatly limited bucket's range of motion and could not be operated independently of the bucket. Next I mounted the thumb at the end of the dipper where the QC is pinned. Now the thumb strikes the bucket near their pivot point so it can't close against the point of the bucket. Considering cutting and extending the thumb to eliminate the interference and to meet the bucket correctly. However that will probably seriously alter movement of the thumb unless the point where cylinder attaches to the thumb is changed. Anybody have experience like this?
Good day and welcome to the forum. I have attached a document that may be a possible solution to part of your problem, there are many options regarding thumb control you can find these on the website under Library >"Adapted applications". In regard to the geometry, I suggest to start by making some CAD drawings that take into account the thumb cylinder and link movement. Kind regards Uffex
Welcome To HEF, oregonion A couple of pictures of your thumb in different positions would be a big help for anyone to advise you on your problem.
After thinking I realize the thumb is just a 2nd class lever; the fulcrum is the pivot point where attached at the end of the stick and top of the QC, The Effort is between there where the cylinder attaches and the Load is the point of the thumb where it meets the point of the bucket. To fix the interference at the point where the QC grabs the bucket pin, the thumb needs to be reshaped while maintaining the distance between fulcrum and effort. This will preserve the range, power and speed of motion of the thumb.
Easier said than done
Can you post a photo that isn't quite so close that shows the entire dipper ? Your set up looks a little strange to me. It should look like this one. IMHO of course. I realize the one in the image I posted doesn't have a quicktach bracket.
Appears that part of the problem is the coupler design moves the bucket several inches inward towards the machine. Maybe redesigning that would be the easiest fix. Or how often will the coupler be used with the thumb? Maybe just direct pinning the bucket to the machine for thumb use? That would be the quickest way to atleast start getting some use out of it.
Good day The combination of coupler + thumb and bucket must have a detrimental effect on stability and capacity, Kind regards Uffex