I am preparing to weld on a thumb mount on my JD 290GLC. Here's a pic with the thumb mounted and the mount ready to weld. As you can see, its natural position is a little more than slightly off center. This is where the thumb wants to sit at full bucket curl at its proper position on the arm. Here's a pic of the thumb. As you can see, the cylinder head on the progressive plate can only move in one axis. My question, is should the mount be welded in it's "natural" position, or should it be welded in the center of the arm? In the center, it will bind at the thumb stow position. In the natural position, it will not bind in any position.
I would say natural position. You don't want any binding. Plus, you’ll probably be the only one to notice it’s slightly off center. Otherwise you’ll have to start disassembling the thumb and measuring parts to see where it’s off and to correct the issue to get it to sit centered. Probably not worth the time and effort.
I don’t know about that. I think i would do some measuring before welding. Check the shims. Work out whats bent. Maybe knock the pin and turn the mount. Would hate to replace the cylinder or link and find out the new one now wont fit.
Ive never seen a thumb cylinder mounted off centre before. Id want to know why before i nailed the tailhold down, and id fix it so that it was centred. Seeing it crowding way off to one side would drive me nuts.
Looking at your cylinder closer, it looks like its not using spherical bearings on the rod and barrel ends, so it wont take up and misalignment. So if your spacing on either your thumb mounting or cylinder rod end mounting isnt bang on centre your tailhold is going to crowd one side or the other. Id make sure both ends of the cylinder have some float on the pins after its tacked into place with the rod both fully retracted and extended before you weld it down solid, otherwise you may have cylinder failures down the road
Yeah, it's bugging me just looking at the pics. I lifted the bucket today and shook it back and forth, to see if there was some play that could be taken up, but the tail still wanted to be off-center. Tomorrow I'll try to pull the pin on the thumb mount and rotate the cylinder rod to see if that makes a difference. This really makes no sense - the bucket and the pins are new, as is the thumb and there isn't much slop in the dipper.
I think if you start measuring the bosses on you bucket, where the thumb pins over the bucket, where the linkage pins to the thumb, and where the cylinder pins to the linkage you'll spot where the problem is pretty quick. One of those joints isn't centred correctly. Probably the only way you'll be able to fix it will be yo have the incorrectly centred bosses machined down and then add spacers to the other side. The other problem you're going to have is as the thumb and bucket start to wear in the end of the stick its going to start to side load the cylinder. Its a less than ideal configuration.
We need a good picture of the bucket pin and the thumb mocked up in location. Is there any play at all between the bucket bosses and the thumb ears? My guess is one of the bucket bosses is thicker than the other to allow for a through bolt or similar pin retaining method.
Measure if the bucket mounting ears are truely centered. Tack in place and verify it works properly before welding.