Bucket and hydraulic thumb coordination

[MrChuckles]

I have a Kubota KX040-4 Mini Excavator with a hydraulic thumb. I've been using it for about 60 hours to pick up logs, rocks, etc., with some that are quite heavy. There have been quite a few times I've picked something up with the bucket fully extended and then extended the thumb to grab it. The problem is when I try to curl my bucket to get under it. The bucket curls okay, but I have a hard time coordinating the electric rocker switch on the thumb so it retracts at the same rate the bucket curls. Several times the bucket curl has forced the thumb to retract.

My question is am I hurting the hydraulics by forcing the thumb to retract? I'm assuming it is pushing fluid past a bypass for the thumb. I am having trouble doing it another way. What are your thoughts? Am I going to hurt my hydraulic system?

 

[Vetech63]

Most thumb valves I have seen have a relief block so you cant damage it. If its a home made job then it may not have.

 

[MrChuckles]

I was hoping for that. It's factory Kubota.

 

[Vetech63]

It shouldn't be a problem then.

 

[Vetech63]

I will say that forcing oil over a relief for extended periods can create heat. I wouldn't do it anymore than necessary.

 

[Vetech63]

Once you get the hang of the operation you should have no issues.

 

[MrChuckles]

I am sure trying not to do it. It doesn't happen too often because I try to position my machine before grabbing on. I'm getting ready to build a stone wall with 1,500 lb rocks and worried about dropping one because of losing thumb pressure.

 

[Vetech63]

How old is this machine?

 

[MrChuckles]

Its a 2018 model.

 

[Vetech63]

Is it under warranty?

 

[MrChuckles]

Yes. I bought the insurance. I accidentally overstated the weight per rock just now. I got 14.1 tons delivered and they came on 8 pallets with about 4 rocks each, so the rocks would average around 450 lbs. There are some that are a lot bigger and some that are smaller. At any rate the wall is off the edge of a slope and worries me to get to and build safely. I'll creepy-crawly my way into it and back out before things go south.

 

[John C.]

Thumb pressures as a rule are set at 2,100 PSI. It is normal to grab onto something with the bucket open and thumb extended and then rolling the bucket into the thumb to maintain the grip and not drop the object. Having said that, if the thumb is set up properly there will be a point where the bucket won't move the thumb anymore because of the mechanical advantage of the thumb over the bucket and linkage. Most operators will set the thumb in a position that is handy to them and then use the bucket curl for actually grabbing on. You will pick up all the nuances before too long.

 

[uffex]

Good day
The thumb is very popular in America however in Europe you will see more Selecta grabs which completely detach when not in use.
If you ask the majority of excavator manufactures they will explain that the arm is not designed to support a cylinder on the back side.
While no doubt sales have driven the demand made by the market my statement will reach many by objection, the principle of the bucket cylinder forcing against the thumb cylinder is a bad idea whilst I am sure many have port relief valves installed the flow from a cylinder being forced inwards will generate more flow that small port valves are capable of taking.
Kind regards
Uffex

 

[MrChuckles]

Thank you. I value your information. I am in the situation where I have to use the tool I have available. I’ll do the best I can to not abuse the relief valves. I wish I had a Selecta Grab but I don’t. Thanks again.

 

[Mother Deuce]

Good day
The thumb is very popular in America however in Europe you will see more Selecta grabs which completely detach when not in use.
If you ask the majority of excavator manufactures they will explain that the arm is not designed to support a cylinder on the back side.
While no doubt sales have driven the demand made by the market my statement will reach many by objection, the principle of the bucket cylinder forcing against the thumb cylinder is a bad idea whilst I am sure many have port relief valves installed the flow from a cylinder being forced inwards will generate more flow that small port valves are capable of taking.
Kind regards
Uffex

Uffex, could you provide a image of Slecta grab please? I have no idea what that is. Thanks

 

[John C.]

If the thumb bracket is welded on properly, you will likely never have a problem with the thumb or the stick due to the engineering. Komatsu recommended for years welding a doubler plate to the bottom of the stick and for a few years the Sumitomo line (Link-Belt/Case) made people weld doubler plates on all four sides of the stick. That doesn't seem to be the case anymore for either line.

 

[uffex]

Good day Mother Deuce
Attached as requested independent open and closing - less likely to foul the boom - when removed aids fuel consumption and visibility - runs from standard option hydraulics - rotating version available if you need - favoured and used in demolition so its up to the job - Opps beginning to sound like a salesman which I am not.
Kind regards
Uffex

 

[uffex]

If you like to see these working there are many on you tube

KR
Uffex

 

[Mother Deuce]

Good day Mother Deuce
Attached as requested independent open and closing - less likely to foul the boom - when removed aids fuel consumption and visibility - runs from standard option hydraulics - rotating version available if you need - favoured and used in demolition so its up to the job - Opps beginning to sound like a salesman which I am not.View attachment 196450
Kind regards
Uffex

Thanks Uffex! I am familiar with the tool and have used something similar. I didn’t recognize the trade name. We are in the U.S. a little more likely it seems to use what we have on hand, rather then invest in “proper” purpose built attachments. It is a mentality that racers call “run what ya brung” and it permeates a lot of what we do. Using YouTube operator Duck Girl as an example with her trailer load of attachments. From a job performance standpoint, I envy her and would love to have those tools at my disposal. However, if someone actually showed up and delivered that attachment trailer to me... I would probably pass out in the seat from shock!
In the meantime, I will be pounding along doing it the way we do it until someone can produce a cost analysis to support the attachments and then find a way to get management to read it.

 

[John C.]

Those are mostly known as clam shells over here. They used to be used a lot in the woods for road maintenance. They are expensive to purchase and maintain, especially if it has a rotation function. The open/close function can be done with the auxiliary valve but a rotate circuit has to be added to the machine for the function. They are also heavy and don't work for underground utilities. For the most part they have been rejected by the construction industry here except for specific applications.