Bucket and hydraulic thumb coordination

[Bubbles]

Just found this thread and am in the same position. Picked up an older KX121-3 and going to be building a boulder wall shortly. When the seller delivered it I hopped in and was monkeying around with it...I had the thumb extended and curled the (empty) bucket into it. He warned me not to do that or I would/could bend the cylinder by putting all that curl force on it while fully extended.

So I have been trying to figure out as I move these boulders around how to curl the bucket once I have the stone picked up...have had a heck of a time trying to back off the thumb at the same rate the bucket is curling.

That is the takeaway from this thread though? that thats what you need to do if you plan on curling when you have something picked up? Or was the takeaway that most modern thumbs will have a relief block so dont worry about it? Or does the relief block not mean you dont need to back off the thumb while curling bucket, but just means you dont need ot be super conservative with doing so (which would result in dropping object)?

How would I know if my thumb has a relief block?

 

[Ronsii]

All modern(and most older) factory thumbs will have overpressure reliefs built in, it's usually when someone added a thumb to a machine and just used an existing AUX valve or similar that they didn't bother to install/convert correctly that you run into trouble.

 

[uffex]

Good day Bubbles
We have made information regarding Thumb installations it would appear from your statements you are looking for the version connected to work in unision with the bucket. All cylinders require port relief valves one solution would be to install a external high capacity port relief to the thumb positive side the pressure could be set as to prevent over pressure by mechanical force.
Kind regards
Uffex

 

[lumberjack]

On my previous 121-3 and current 57-4, I’ve never worried about pushing the thumb in with the bucket, never had a problem, and never expect to have a problem. Coming on 1500 hours between the pair, primarily doing tree work.

 

[keif]

On my Tak if I grab something with the thumb, then curl bucket, then easily release the thumb they move I unison and keep a good hold. I love my thumb despite what europe says its powerful though and takes some "gentle touch".

 

[KSSS]

On excavators that only have a single aux circuit that runs the thumb and valves off that to run other attachments like hoe pacs, breakers and mulchers that circuit has to have the psi set low enough as John C states to allow the thumb to give when over pressured by the bucket. That setting is not automatic, it needs to be set that way. Some attachments, like mulchers and mowers prefer a higher psi setting to keep from going over relief and 2K is pretty low. So a machine that leaves the factory without a thumb may be set to a higher psi setting on the aux. If you put a thumb on the machine, the psi on the aux. needs to be set so you don't break the thumb cylinder if you over pressure the bucket. Some machines have an additional circuit and this is ideal in my view, one circuit powers the thumb and set to the appropriate psi for thumb work. The additional circuit runs attachments with a higher psi setting on the relief so you can get the most out of your attachments. Reading through some of this it seemed to me that some suggested that the thumb circuit will automatically go over relief, it can if it is set low enough to achieve that, but you want to confirm that before you turn your thumb cylinder into a pretzel.

As far as thumbs themselves, I am pretty particular on the style and build of a thumb on the ones I buy. There are some really poor designs out there in my opinion, especially in the area of the claw design. I like the progressive link (prolink) style thumbs. Allows for greater thumb articulation, especially helpful doing rock work but I like it for everything. Wouldn't have a thumb without it. As far as learning to feather the thumb and the bucket at the same time, it takes some time to master that, but with practice it becomes easy.