Hydraulics for backhoe thumb question

On my back hoe (JD500C) the loader bucket leveling is a function of the mechanical linkages / pivot points. It is parallelogram configuration with four pivot points. One leg of the rectangle is the bucket tilt cylinders so the length varies tilting the bucket. As the lift cylinders push the main loader booms up that parallelogram adjusts keeping the same angle.

Another setup I've seen that is hydraulically based does not use valving per-se, but uses a sort of a "servo" cylinder that is mounted at the base of the pivot and by being appropriatly sized will "trim" a front cylinder that is the tilt control for the "front end". It works pretty much the same as the setup on my backhoe, but replaces one physical linkage with a hydraulic one. I've seen this setup used on tele-handlers mostly. Possibly your 580CK uses something similar. I would think that they would avoid using a true valving setup since the complexity would be rather high.

The backhoe thumbs I've seen don't appear to do any sort of angle sensetive control. I've seen fixed thumbs where the bucket cylinder does all the work, and active ones that use a seperate control. In both cases it does not appear that there would be a need for angle sensativity since whatever you are holding is pinned between the bucket and the thumb, neither of which will move relative to each other as the boom and or crowd functions are operated.

The factory service manuals will tell you a lot. That's one of the first things I got for my backhoe and the set was

If this is the machine I am thinking of, there is a level compensating slave cylinder on the right side of the machine. This adds or subtracts fluid from the bucket tilt cylinder as appropriate. The hoses to this cylinder don't go back to the valve body, just across the bucket tilt lines. It is a fairly common method to accomplish this action.

Shawn

Eric, I am a new backhoe owner and have been thinking the same (about a thumb) for the hoe. Looking in the Machinery Trader and online, there are fixed and movable thumbs. Hunt around your area for someone in the demolition business. They would be a good source of info from someone who uses one every day. Might even let you try one on their machine.

One interesting movable thumb utilized the extenda-hoe movement. Others required aux hydraulics.

Bob

On Mon, 24 Jan 2005 15:36:42 -0500, the inscrutable "Shawn" spake:

You mean the bucket/thumb stay the same in relation to the ground, rather than the arm, during the raising/lowering/extension/retraction? That'd be cool, expensive, and a bitch to fix. ;)

On the front of the tractor the bucket keeps it's angle the same in relation to the ground. What I want is for the thumb to follow the backhoe bucket. So when it grabs something the bucket can be curled without either dropping the load or being prevented from curling further. One way I thought of is to use an accumulator connected to the thumb that is pressurised less than the pressure that the bucket cylinders. That way the bucket could put pressure against the thumb. The accumulator would just fill with oil as the bucket curled against the thumb. But that idea seems expenzive and inelegant. There has to be a better way. Maybe Northern can tell me how to do what I want. ERS

Not really a needed mode of operation - does not buy you much, excessively complex. A manually set thumb is quick, easy (and inexpensive) to build, stays out of the way when not in use, and works quite well for those tasks you might want a thumb for. Reach, grab, pick, drop. It also does not add a lot of dead weight to the bucket area; weight which will work against picking up whatever you are trying to grab. My hoe can supposedly apply 9000 lbs of force to dig with (curling in at the bucket lip), but it can only pick _up_ about 1500 lbs at full reach. Add a bunch of hardware and plumbing, and you subtract payload.

If you are seeking the full pick & place mobility a log loader offers, you need a log loader. If you get your superthumb, you still won't have rotation, and your reach is awfully short. A TLB is a great general purpose machine, and I have moved a lot of logs with mine, since it the only thing I have to to that with - but turning it into a log loader is no more practical than turning it into a bulldozer.

The "easy" way to do what you describe is to have a "thumb" (or perhaps "fingers") that is mounted to the bucket itself, ala a clamshell bucket. That way moving the bucket moves the thumb, and you can apply the pressure you want to the tumb, then curl the bucket without changing the clamping pressure. But it will probably get in the way of digging. Someone may have tried this, so go look for design ideas and design flaws by seeing if you can find such a thing, prefereably well used, so the flaws show up.

I doubt the accumulator would work - the load can squeeze it and make room to fall out. If the load can't squeeze it (too strong), then the load is likely to get crushed as you try to squeeze it with the bucket, since the load is in between.

IMHO, YMMV, etc....

And I can't honestly think of a purpose for it. When you're moving something in the hoe, just crank it all the way up & go. Auto-leveling doesn't seem like it'd do much.

Greetings Lawrence, I didn't think the accumulator idea through, obviously. Your post points out something I didn't consider, the varying pressure I might put on the clamped item. I'm not looking for a log loader. Even though I will be picking up logs from time to time. But when that happens they will be elevated and then cut. The person doing the cutting will be aware of the chance that the log might swing when cut and will act accordingly. Having the thumb move with the bucket would be really helpful for me. Several months ago I rented a tracked excavator. Though small it had a lot of lifting power. I had to move several large concrete slabs and since the thumb didn't move with the bucket there was a lot of fussing around picking up and positioning the concrete slabs. Since lots of rocks will be moved the thumb will be very handy. And the thumbs that are positioned with a pin would be a real headache for me. I really need the machine to do the work. Your idea of mounting the thumb to the bucket is intriguing. Maybe some changes to the bucket will be in order. Thank You, Eric R Snow

Eric,

You just need more practice using your hoe. You can release fluid on the thumb while applying full pressure to the bucket to roll the bucket in. (feather one valve while other is pulled all the way) Reverse operation to roll bucket out.

Copy the design for your thumb from any similar hoe.

Doesn't your neighbor do this for a living? he can show you how. Not at all hard once you get on to it.

Remember, running a backhoe is the most fun that can be had, with all your clothes on.

Karl

When I was clearing trees from a decent sized area by myself I found that the front loader bucket was more useful. I did what I referred to as "backhoe jousting".

I'd drop a tree and then bring the backhoe around from the "back end" where the stump was. I'd position the loader bucket centered above the downed tree with the cut end a foot or so past the back of the bucket. I'd lower the bucket so that it was flat across the tree and hook a chain around under the tree to an attachment point at the top of the bucket. When I raised the loader bucket a couple feet and tilted the bucket back slightly the entire tree would "levitate". This allowed me to walk along the side from the bucket to the tip and back again taking off all of the side branches. I could then start at the tip of the tree and chop the trunk into sections until taking the last cut just in front of the chain. I could then load all the logs into the bucket and carry them off.

For moving rocks I certainly wished I had a thumb on the backhoe, but I don't think I would have had any need for one to move with the bucket. I never had any problem getting the bucket around and under a rock, so if I had a powered thumb that I could then swing down to hold the rock against the bucket that would have worked fine. When I picked up the boom the angle of the rock relative to the ground might vary, but should make little difference as long as the thumb was holding it.

Pete C.

You guys are confusing me. All the backhoe thumbs I know about do not use hydraulics, they are just a fixed "fork". You curl the bucket to shove a rock or stump into the thumb so it doesn't continue to fall out of the bucket.

(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

You mean, top-posted because you're too lazy to delete the rest of the content and want people to scroll up and down to see who the heck you're talking to, you mean?

That reminds me.... a little tip for anyone who might not know - a friend with a JD backhoe recently purchased a complete set of manuals for the military version of his machine (parts, service, maintenance, etc., several thousand pages) on a CD for $10, the everyday price on Ebay. A real bargain.

Wayne