Backhoe Thumb Hydraulic Options

[lostcreekranch]

Stopped at local Kubota Dealer to get some parts and asked one of the tractor sales guys to work up pricing on a Grand L 5460 with FEL and back hoe. He quoted BH with 18" bucket at about $9,000. To add a hydraulic thumb to BH added another $3,000. A Grand L with FEL and BH for over $60 K? Don't think so.

 

[dfkrug]

The more I think about it, wouldn't a design where one could push the other back be utterly
useless? If the bucket could overcome the thumb before hydraulic relief cut off the flow to the curl cylinder, wouldn't
every "pinch" wind up with a collapsed and useless thumb?

No, it would not be useless at all. There would still be quite a bit of pinching force exerted before the bkt pushed the
thumb back (or vice versa).

What I am trying to share here is another design choice that can be made early on in the hyd thumb choosing/building
process. A lot can be done up front before you are constrained by choices already made, like converting a mechanical
thumb to hydraulic. Or fixing a sub-optimal hyd thumb setup that keeps bending rods.

As the OP, you might want to read this long thread:
http://www.tractorbynet.com/forums/...20-bh77-has-anyone-considered-converting.html

When I approach a design like this, I am trying to consider numerous factors wholistically: since I am going to build
and use it, what can I do to minimize the cost? Can I accept the trade-offs that might be made doing it in a less
expensive way? What choices can be made in the design to make it easier to build? Etc.

The simplest way to build a hyd thumb is to design it so that you don't need to add a work-port RV. So I did
it that way. Not every aspect of my specific design works with other hoes, and it did not allow me to use the
cheapest components, like tie-rod cylinders.

 

[avc8130]

No, it would not be useless at all. There would still be quite a bit of pinching force exerted before the bkt pushed the
thumb back (or vice versa).

What I am trying to share here is another design choice that can be made early on in the hyd thumb choosing/building
process. A lot can be done up front before you are constrained by choices already made, like converting a mechanical
thumb to hydraulic. Or fixing a sub-optimal hyd thumb setup that keeps bending rods.

As the OP, you might want to read this long thread:
http://www.tractorbynet.com/forums/...20-bh77-has-anyone-considered-converting.html

When I approach a design like this, I am trying to consider numerous factors wholistically: since I am going to build
and use it, what can I do to minimize the cost? Can I accept the trade-offs that might be made doing it in a less
expensive way? What choices can be made in the design to make it easier to build? Etc.

The simplest way to build a hyd thumb is to design it so that you don't need to add a work-port RV. So I did
it that way. Not every aspect of my specific design works with other hoes, and it did not allow me to use the
cheapest components, like tie-rod cylinders.

This is EXACTLY why I posted rather than just diving in.

I feel "fortunate" that Kubota was nice enough to "give" me the cylinder mount on the dipper stick. I almost feel like I am leaving food on the table if I don't take advantage of it.

As you can see, this thread has gone round and round and round on options.

There is so much terminology thrown around that I'm not even sure what the options are any more. I will try to summarize:

1. A "valve" similar to Kubota's setup added to the current stack with a foot control.
2. A "valve" added to the power beyond somewhere with a fully separate lever and system.
4. A diverter off of one of the existing functions to provide independent control of the thumb cylinder.
5. A diverter added to the curl cylinder to allow the thumb to function along with the curl like a pinching tong.

All have their advantages and disadvantages.

As far as the mechanics go, I plan to use the existing cylinder mount on the stick and build my thumb off the bucket pivot just like Kubota did:



Their mechanical design looks excellent and not TOO terrible to replicate, especially if I cheat a bit and buy their pins.

ac

 

[J_J]

All righty then.

I with draw all my suggestions.

 

[avc8130]

All righty then.

I with draw all my suggestions.

That wasn't what I meant and I am sorry if you took it wrong.

I greatly appreciate your advice and wealth of knowledge. I am the one that is all messed up.

I get lost in the terms and techniques and all of the different suggestions really had me confused so I just wanted to summarize.

If it wasn't for great knowledge bases (such as yourself) on this forum, it would just be a bunch of guys posting pictures of holes they dug rather than guys doing crazy things like trying to reinvent the wheel on a backhoe thumb!

ac

 

[J_J]

I know, I was just joking.

Just do the best you can with what you have and what you know.

Be glad to help.

 

[avc8130]

I know, I was just joking.

Just do the best you can with what you have and what you know.

Be glad to help.

I found it!

The one side of the valve stack had an ID plate on it. It looks like Kubota sources the stack from these guys:

KOSHIN SEIKOSHO,LTD

Are stack valves generally compatible with other manufacturers? Do I need to find a US distributor for Koshin to stand a chance at an affordable factory equivalent setup?

ac

 

[dfkrug]

Are stack valves generally compatible with other manufacturers? Do I need
to find a US distributor for Koshin to stand a chance at an affordable factory equivalent setup?

No, and yes, I would say. I have purchased the modular stack valves from Prince in the past, and they
look totally different from the stack valves on all the hoes I have had or seen.

Anyway, to avoid the exhorbitant Kubota prices by getting an section from the manufacturer is a worthy
pursuit, but be prepared to be disappointed.

Putting an aftermarket monoblock valve with PB upstream of the hoe valve stack would be much more
economical, and you could install it wherever you want.

The L45 is a fantastic TLB with 2 hoe hyd pumps (swing and other), giving you a choice of either for
your added manual spool valve.

That's a hefty thumb that Kubota builds. What diameter pin do they use? The shared one.

 

[avc8130]

No, and yes, I would say. I have purchased the modular stack valves from Prince in the past, and they
look totally different from the stack valves on all the hoes I have had or seen.

Anyway, to avoid the exhorbitant Kubota prices by getting an section from the manufacturer is a worthy
pursuit, but be prepared to be disappointed.

Putting an aftermarket monoblock valve with PB upstream of the hoe valve stack would be much more
economical, and you could install it wherever you want.

The L45 is a fantastic TLB with 2 hoe hyd pumps (swing and other), giving you a choice of either for
your added manual spool valve.

That's a hefty thumb that Kubota builds. What diameter pin do they use? The shared one.

Yeah, I already see the disappointment. I think I am going to go with a diverter setup. That will keep the controls on the 2 current sticks, and let me have full control of the thumb.

I believe the pin is 1". I was hoping to find one locally to look at. A member was nice enough to give me some pics of his:

Thumb Photos by avc8130 | Photobucket

ac

 

[dfkrug]

This is some data from a thumb manufacturer.

CautionCautioCautionn

HYDRAULIC PRESSURE ON THUMB CYLINDER SHOULD NOT
EXCEED 2000 PSI. IT IS ESSENTIAL TO PERFORM TESTS TO
ENSURE THAT THE BUCKET AND ATTACHMENTS ALWAYS
OVERPOWER THE THUMB. FAILURE TO DO SO WILL CAUSE
DAMAGE TO THUMB, PINS, CYLINDERS, BRACKETS AND STICK.

AC:

The above quotation from a maker of thumbs illustrates my earlier point. They are
marketing a design to be installed on multiple different and unknown hoes. The maker
has fixed some variables (like cylinder diameter) that can not be easily changed. This
is the antithesis of custom design where you optimize your thumb for your hoe.

Making and selling a generic hyd thumb is extremely difficult because you would really
really want a workport RV in the thumb valve. And you would have no knowledge of
the customer's hoe valve(s). That's one of the reasons that aftermarket hoes were so often
sold with PTO pumps: the maker had little idea of how to tie into the huge number of
hyd systems out there.