View Full Version : Thumbs for excavators
11-06-2007, 09:30 PM
Can you all explain to me the different types of thumbs out there? I know what a thumb is and what it does. I know some are operated by a hydraulic cylinder. I know some are stationary and that you move the bucket toward the thumb to clamp what ever you want to hold. Other than that I dont know all the specifics. Please educate me. :)
11-06-2007, 10:10 PM
Progressive Linkage- looks like the bucket linkage, lets more movement out of the thumb getting grabbing stuff closer to the machine, really good in the forestry/land clearing.
Direct link- just a cylinder pinned to the thumb, good for heavy duty grasping.
Mechanical link- welded directly to the stick, the operator has to get out of the cab and man handle the thumb down and cleverly pull and push pins in, the thumb will be at a 90 degree angle to the stick, that version is the cheap way out.
11-06-2007, 11:29 PM
it might be the cheap way out, but i have customers that can set 3000lb stones with a 10000 lb machine and make it look easy....i think sometimes it helps to elimate the thought process sometimes and keep it simple...it can be tough to convince customers sometimes!!!!!!! because we all know that customers are the best operators around!!!!!! j/k:waving:
11-07-2007, 10:51 AM
I've seen excavators that cracked the end of the sticks due to the mechanical thumbs, a lot of times they grab rocks with just the wrong amount of pressure and the end of the stick rips right open.
11-07-2007, 02:02 PM
I've heard of that as well. This guy I know back home had an older Hitachi UH something, it was a real dinosaur, but it was the first excavator I ever ran at the ripe age of 11. Anyway, he had a big mechanical thumb on that thing and I remember him telling me that you had to be careful with rock otherwise you'd break the stick in half. With a hydraulic thumb, it's still feasible, but chances are the rod will lose pressure and curl before you bust the stick open.
Hydraulic progressive link thumbs are the preferred choice out here. Lots of range of motion, lateral stability because of the links, I've seen what happens when you bump a direct link thumb wrong, tears it off the machine. A guy back home had a direct link thumb on a backhoe that got sheared right off because the thumb more or less twisted. The direct link thumbs also exert more pressure on the object, which is good most of the time. However, when placing stone, it's a real PITA if you need to roll the rock just right and you're out of thumb travel. Then you have to physically move the machine. Plus, your rock pile always seems too close and you can never grab the stone correctly. With a progressive link, wherever you can get the bucket, the thumb can get to it.
11-07-2007, 02:37 PM
A old mechanical thumb (non hydraulic) is better than nothing but you can as the others said you can twist and break things. It takes some skill to use a mechanical thumb. The most common thumb is direct link.
In my mind excavators should be standard issue with a thumb.
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