Backhoe Mechanical or Hydraulic thumb?

[jchealey]

I have been thinking about getting a thumb for my backhoe. I used one on a large excavator to tear down a house and rip a tree out of the ground and it would be a useful addition to my lazy man tools. Do you have any recomendations as to how to size, or mechanical vs Hydraulic? I have plenty of pressure for the Hydraulic.
From the pin to the end of the teeth is 22 inches. Backhoe is a Woods 1050.

Jerry
L48

 

[rScotty]

I have been thinking about getting a thumb for my backhoe. Jerry
L48

I have had hoes with and without a hydraulic thumb. Before I had a hydraulic thumb I just had a piece of metal that I would pin onto the dipper arm. I guess you could call it a mechanical thumb, but it didn't move.

The hydraulic thumb makes the hoe into a whole new implement. I can pick up and place heavy things with it now. Not just rocks, but even fairly fragile things. No more dragging things to the side to get them to slide into the bucket, it's just lower the bucket and grasp them.

There's a bit of a tricky relationship between the thumb and its geometry. You want the bucket to always be able to overpower the thumb and also design it so that the thumb can never get into an "over-center" position. There also needs to be a pressure relief valve or circuit so that the lines to the thumb don't burst when the bucket forces it backwards.

All in all, I think that using it has given me the understanding to design one myself now if i had too....but it was worth while to go ahead and buy the proper factory one for my hoe. Costly, but worth it.
Good Luck, rScotty

 

[hr3]

Hydraulic for sure,, I have a mech. one now and wish I had spent the money when I bought the hoe.. Now I have to convert it..

 

[Kyle241]

Hydraulic if you can afford it.

 

[20 20]

The obvious answer on which one is better hyd-vs-mech would be hyd. With that written I have had both and no matter what both have been VERY usefull. I built my own{3or4} mechanical and hydraulic, I bleieve one of the most important things is to make the thumb weaker then the bucket. Much cheaper to fix a thumb JMO.

 

[cal1]

How do you do that?

 

[20 20]

How do you do that?

If you're asking me then I'll try to give a quick explanation. I use material {if mechanical } that will bend/break instead of causing damage to the arm/bucket/cylinders/etc. On hydraulic units there are different ways of making the thumb cylinder weaker then original equipment. Hope this helps what I wrote.

 

[hayden]

I'd get a hydraulic thumb if at all possible.

 

[cal1]

Thanks 20 20, I was wondering how to make a hydraulic unit that would be weaker than the arm. Guess you'd need to be pretty familar with both the existing system and the thumb. I don't know if there are any adjustments to reduce power on a piston. I've done a lot of electronics (mostly digital) but wish I had more usable knowledge.

 

[rScotty]

Thanks 20 20, I was wondering how to make a hydraulic unit that would be weaker than the arm. Guess you'd need to be pretty familar with both the existing system and the thumb. I don't know if there are any adjustments to reduce power on a piston. I've done a lot of electronics (mostly digital) but wish I had more usable knowledge.

Nothing wrong with being familiar with the existing system, but it's not really necessary. That's because it's normal practice is to plumb the thumb system with relief valves anyway. The reason being that either the bucket forces the thumb or the other way round....and in either case both systems have to have relief valves and bypass lines to avoid breaking something expensive. So just build it that way and as a bonus you can simply do some cautious experimenting and set the relief pressure appropriately.

That's how most backhoes work and it's also how Kubota solves the problem of relative hydraulic strength with the hydraulics in their stock backhoes. Our M59 came with either 8 or 10 adjustable relief valves mounted in a double row right onto the backhoe lever manifold. The bypass lines are internal to the valve block. Kubota set the pressures at the factory, but there's been some adjustment required since. That's pretty much typical.
rScotty

 

[graydog]

I just bought a new L39 TLB, and had the dealership install a hydraulic thumb like comes on the L45.
It didn't work. Dealership sent me another cylinder, which when swapped out would run the thumb to (apparently) full extension, but hasn't got the strength to pick up a chunk of firewood.
Follows the bucket in curl and extension, and extends itself slowly, retracts fast.

Dealership (far away) is recommending that I go see dealership (closer) which is pending,
but can anyone comment on the problem?

Thanks!

 

[dfkrug]

That's because it's normal practice is to plumb the thumb system with relief valves anyway. The reason being that either the bucket forces the thumb or the other way round....and in either case both systems have to have relief valves and bypass lines to avoid breaking something expensive.

Is it normal practice to provide work-port RVs on both the bucket and
thumb cylinders? On industrial hoes, anyway?

When I designed my hyd thumb, I just made sure that either the thumb
or the bkt, when actuated, could not exceed the forces that the other
could resist without damage. That means that when the bkt is moving
against the thumb at maximum mechanical advantage (about half way),
the thumb's structure was built strong enough, and the cylinder's
internal pressure did not exceed the cylinder's or the hose's ratings. And
the other way around.

This also means that I used a thumb cyl of about the same bore as the bkt
cyl, and it could handle 3500psi. No tie-rod cheapie cyl here. My hoses
are rated at 4500psi wp. I used no work port RVs and I have many hours
on my hyd thumb with no problems. My CUT operates at only 2500psi; the
L48 (I think) is about 3000.

BTW, designing a fixed thumb to withstand all the worst case forces the
bkt can dish out is similar. You have to size it right, and use at least
1" pivot pins. And the enormous bkt forces can distort the thin metal of
the dipper stick if the thumb welds and brackets are not done correctly.

 

[rScotty]

Is it normal practice to provide work-port RVs on both the bucket and thumb cylinders? On industrial hoes, anyway? /quote]

As far as I know it is. The construction backhoes I've looked at seem to have relief valves everywhere. Not just on the bucket and thumb cylinders, but on every circuit and in both directions. I'd have to go out and count, but I seem to remember that our Kubota M59 has 8 relief valves on the standard backhoe spools plus two more when the thumb was added.

Doesn't it increase the hose pressure when two cylinders are working against each other?
rScotty

 

[CurlyDave]

... Do you have any recomendations as to how to size, or mechanical vs Hydraulic? I have plenty of pressure for the Hydraulic...

Jerry
L48

If you like getting out of your seat and dismounting to adjust the thumb get a mechanical one.

If you think you would like having the thumb in the "almost right" position sometimes and the "surely wrong, but I am too lazy to get down and adjust it" position other times, get a mechanical one.

If you think it would be fun to climb over a pile of rocks to adjust the thumb, get a mechanical one.

If you are going to use it a lot get a hydraulic one.

If you are only going to use it a few times a year, the mechanical one is fine, if you are going to use it frequently, the hydraulic wins every time.

 

[rScotty]

I just bought a new L39 TLB, and had the dealership install a hydraulic thumb like comes on the L45.
It didn't work. Dealership sent me another cylinder, which when swapped out would run the thumb to (apparently) full extension, but hasn't got the strength to pick up a chunk of firewood.
Follows the bucket in curl and extension, and extends itself slowly, retracts fast.
Dealership (far away) is recommending that I go see dealership (closer) which is pending,
but can anyone comment on the problem?
Thanks!

OK. I'll comment on the problem. In the first place, stick with it. You'll like the hydrualic thumb. It makes a BH into a whole new tool and worth it.
But I'm curious, why put an L45 thumb onto a new L39 in the first place? Why not use something designed for the L39?

Thinking about it a bit....I realize I'm assuming that the L39 and L45 both have the bucket and thumb set up to use the same common pivot point. So that it is what is known as a "pin-on" geometry. If that's so, the mechanical motion could probably be made to work. And an L45 thumb control could provide the hydraulics. Thumb controls are separate from the rest of the system anyway....so maybe it's not so far fetched.
How's it coming?
rScotty

 

[J_J]

Did someone use spools for the thumb that had regen on it?

As far as power, the pressure is not additive. Any excess pressure will go to relief.

If two cyl are being used at the same time, the force is additive. A cyl with a push force of 5000 lbs parallel with another cyl with 5000 lbs of push force will have a push force of 10,000 lbs. Mechanical forces may add or subtract the force.

Even is you used the same cyl for the bucket and thumb, all the mechanical connections would have to be the same to be equal. If one is different, for whatever reason, the force will not be equal. In fact, one cyl might override the other and push the shaft into the cyl, or bend or break something.

The thumb is there to assist not compete with the bucket cyl.

If the thumb set up is not working, something is not set up correctly. Some pressure readings might help trouble shoot the system. The retract on a cyl should be faster, but if the cyl is using a regen circuit, fast extend will make it faster.

Where one might get into trouble is if a large cyl is pushing on a smaller cyl and causing the pressure to build in the small cyl, it could exceed the rating of the cyl, and or the hose. A work port relief would prevent that.

I have to say that your dealer is doing you a disservice giving you the BH with things as you say. Did they not test it ? Did you not insist they show you how it works. Just seems like people are becoming more untrustworthy. They should know you can not fool all the people all the time.

 

[graydog]

rScotty and J J -- Thanks for helping this carpenter along.
When I said a thumb like the L45 I only meant they seem to come with one. I imagine the dealer used a kit intended for the L39, although it sounded like they were having to invent the idea. Hmmm.
The demonstration we got on delivery was extensive and useful, but since we intended to mow to begin with we had him set up that equipment, and didn't dwell too long on the backhoe. I wasn't the first one to use the thumb either -- my son got to stirring dirt and logs and mentioned that the thumb wasn't doing much of anything. So it's possible that on its first squeeze it blew something.
Spools and vallves and ports and cylinders are new to me -- I'm at the stage of learning what the questions are. We've rented equipment for decades, but never had to look after it.
Not mad at the dealer -- he's 350 miles away, and the nearer one is 70 miles, so looks like I need a trailer. I am confident that this will get sorted. Sure like the tractor.

 

[J_J]

When you activate the thumb, do you hear the valve relief activate, or screech?

If that same valve is controlling the thumb, then a hyd gage at the IN port will tell you the pressure being utilized by any cyl that the valve controls, or any valve downstream.

Well, I hope we can help your solve your problems.

Perhaps you could study up on some basic hyd and from there, just ask questions.

Knowing how things work is important, to determining that something is not working correctly.

When you ask questions, please give all the facts. What where, when, model, etc.

 

[J_J]

How about some pictures of the bucket and thumb.

 

[dfkrug]

Is it normal practice to provide work-port RVs on both the bucket and thumb cylinders? On industrial hoes, anyway? /quote]

As far as I know it is. The construction backhoes I've looked at seem to have relief valves everywhere. Not just on the bucket and thumb cylinders, but on every circuit and in both directions. I'd have to go out and count, but I seem to remember that our Kubota M59 has 8 relief valves on the standard backhoe spools plus two more when the thumb was added.

Doesn't it increase the hose pressure when two cylinders are working against each other?

My hoe has only 4 shock RVs for the 6 valves it came with, as I recall. Six
valves on a typical hoe (without hyd thumb) means that you could have
a total of 12 work port reliefs. It makes sense that industrial/commercial
hoes would use RVs everywhere.....the pumps are so fast that huge
kinetic forces build up to be stopped in an instant by the valve.

The L39/L45/L48/M59 all have dual-pump hoes, so each independent
system would have its own pump-RV, too. Dual pumps also allow you
to put added valves (hyd thumb) on either circuit. If the thumb valve
operates off the swing pump, then you could have the bkt push
against the thumb in an active manner, so the element putting out the
greatest force would push the other back. So when both valves are
on, the internal pressure could not be greater than the pump-RVs of
each pump. If one valve was off, and the other element was pushing
on it, then the internal cyl and hose pressure could definitely go
higher. I try to design for it.

You can also activate the bkt and thumb in parallel with a one-pump
hoe by pulling both levers at the same time, and then one element
pushes and moves the other, like a grapple.