My Manual Thumb To Hydraulic Conversion

[joe--h]

Fixed position sucks, although still better than nothing. I think with it fixed I end up having the bucket in a less than ideal position that with hydraulics could be avoided. Get the bucket in position then close the thumb would work much better than trying to fight the bucket and whatever onto the thumb.
I've been thinking having more thumb movement would be the answer but I can see that it isn't necessary if the bucket moves first.
Joe H

 

[Willie B]

Thanks go to a fellow member (uffex) for posting some valuable information in the excavator forum in regards to backhoe thumbs.
This is his post.
"Good day JHead
To be correct providing relief is only part of the issue you must refill the opposing chamber to prevent cavitation, attaching the file with the information is to large for the site, however if you go excatech.org - library - adapted applications - thumb ? & answers. I hope you will find the information helpful there is much more of the web site, any questions please drop me a line.
Kind regards
Uffex"
I went to that site and found all the answers to my concerns about the pressures a thumb cylinder undergoes when the bucket cylinder is pushing against it.
I may not need a relief valve because my thumb and bucket cylinders are nearly identical in size.
If that is the case then I can remove the temporary hose clamps on my hydraulic lines and bolt them down properly.
This is the page in that document that addresses the relief valve.
View attachment 235067

I built a thumb for a Case 580K with extend a hoe. It worked like a charm, but the third valve on the loader I had rerouted to supply the thumb apparently didn't have port relief. It wasn't a long while before it bent the rod. At the time, 15 years ago, the guy at Cassella Hydraulic added a one piece relief valve. Both hoses from the supply went to this relief, two hoses connected the valve to the ends of the cylinder.
That worked well until a mishap. It was a "welded T cylinder" The but end of the cylinder pinned on a 4" wide tube welded to the butt end. The pin sheared on one side causing sideways thrust, bending the rod.
Best picture of old thumb:




Only picture I found of the first thumb.
Next prototype was a very different design & is still working fine.



This was a much better functioning thumb.
This picture with the reinforced 12" bucket. Great rock handler!