Backhoe Thumb Hydraulic Options

[chewsdad]

Jumping into this discussion. I built a thumb for my hoe using heavy angle iron and a 19" stroke cylinder. I used a diverter valve plumbed into the right side stablizer. Handle towards tractor - stablizer, handle towards hoe - thumb. RE the different sized cylinders. Good analogy: a pickup nose to nose with a big rig. If there is no mechanism - relief valve - for the smaller to go backwards something will give. I bent the ram on my thumb cylinder by pushing too hard against it with the bucket. Now I have a relief valve set at 2000 lbs to allow the thumb cylinder to retract automatically if the larger curl cylinder pushes too hard. If you only gripped with the thumb then no problem, but, oops and the thumb cylinder was ruined. Lesson learned. Using Surplus Center for parts and scrap (free) heavy angle iron, my thumb cost about $500.

 

[J_J]

chewsdad,

Thanks for posting about your thumb experiences.

Most people will not admit failure or misapplied applications in some situations.

Those that have not had a thumb collapse probably have a matched force applied.

However a simple relief will solve the problem of the thumb being overpowered.

I am not sure the low budget BH will have work port reliefs.

If one builds there own stack valve, they can order whatever they want in each spool, including work port reliefs.

 

[ishiboo]

For some reason, I keep thinking that if I put two cyls head to head, lock down, and apply pressure, even with relief, the larger cyl will cause the other cyl to go into relief and retract.

If you really want to know, just tee a gage into each cyl circuit.

This is how the OEM Deere bucket clamps (thumbs) work. They are designed to be over-powered by the curl so you don't mess anything up. You can still put a ton of force on them and do whatever you can safely accomplish with the thumb.

 

[dfkrug]

I am not sure the low budget BH will have work port reliefs.

Does that make Kubota's BT1100 hoe, the one that comes with the OP's L45 tractor, a
"low budget" hoe? I have a lot of respect for Kubota's engineers and how their design
did NOT use work-port RVs for the thumb (and maybe not the bkt valve). I do not have
access to parts diagrams for these hoes, unfortunately, to check.

There is no substitute for good design engineering.

 

[chewsdad]

A simple three port relief in the line to the extend side of the cylinder with the "back to tank" port teed into the retract side of the valve is sufficient. And an edit I used the left stabilizer, sitting on the hoe with the seat turned around it is on the right. Maybe a "leftie" would like it on the right side (backwards left). A diverter was cheap compared to a new stack valve. On a 39 year old Massey Ferguson used mostly for digging out old stumps and pushing over unwanted trees.
Speaking of low budget hoes. I resemble that remark - $7,000 plus $500 for thumb plus many hours making new pins to take slop ourt of loader plus new pins in hoe this winter. Gaining in value all the time. Nice looking tractor with new front tires ($250) and good rear tires and a good thumb. Every time we drive by one of the "thumbless cousins" my wife has consoling words for the poor handicapped thing.

 

[avc8130]

Does that make Kubota's BT1100 hoe, the one that comes with the OP's L45 tractor, a
"low budget" hoe? I have a lot of respect for Kubota's engineers and how their design
did NOT use work-port RVs for the thumb (and maybe not the bkt valve). I do not have
access to parts diagrams for these hoes, unfortunately, to check.

There is no substitute for good design engineering.

Kubota was kind enough to put all of their "Illustrated Parts Diagrams" right on their website for all to see!

Kubota Tractor Corporation - Parts List

ac

 

[dfkrug]

Kubota was kind enough to put all of their "Illustrated Parts Diagrams" right on their
website for all to see!

That's great. Tried the link to look at the L45 (BT1100) control valve to see how it worked. Not too clear, but
it seems that they use one stack for both pumps, and use a "mid-inlet". I don't know what they mean by
"shuttle valves". Anyway, the best bet to add your own non-OEM valve with PB is before the right hand inlet
to the stack.

 

[avc8130]

That's great. Tried the link to look at the L45 (BT1100) control valve to see how it worked. Not too clear, but
it seems that they use one stack for both pumps, and use a "mid-inlet". I don't know what they mean by
"shuttle valves". Anyway, the best bet to add your own non-OEM valve with PB is before the right hand inlet
to the stack.

I think I'm leaning towards a diverter off of the swing. That way I will be able to control the thumb quickly with my left hand in a side to side motion just like the curl is with my right hand. I'll use a momentary switch on the control knob to select the thumb only when I hold the button, otherwise it will be swing function.

ac

 

[dfkrug]

I think I'm leaning towards a diverter off of the swing.

Oh, I thought you were leaning toward a manual lever-operated valve. Multiple choices; no
right/wrong way.

Something else to consider: the manual valves I buy can usually handle 3500psi max pressure.
My solenoid valve is rated for 3000psi max. I would not get anything rated less than 3000psi,
unless you use a cheaper valve and spend your savings (and more) on a RV.

Post your results....a hyd thumb has doubled (at least) the usefulness of my hoe.

 

[CDN Farm Boy]

There is another way to control the thumb ... I run my thumb cyl in parallel
with my curl cyl, and put one small 12v spool valve on just one of the cross-over hoses. This way, when
I flick a toggle switch, my bkt and thumb act like a grapple. Flick it off, and the thumb is anchored in a fixed
position. A push button on the right joystick would also work here.

This is an interesting idea that I haven't seen before, and sounds like a neat idea. What valve did you use and got a pic or drawing of the plumbing layout?
Would this eliminate the problem of one overpowering the other and work kind of like a dual lid setup on a grapple bucket where one will contact the item, stop until the other makes contact then tighten together?

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.

With the 2" cyl on my thumb and the 2.5" on the curl, I've had no issues so far that I'm aware of due to the different size cyl

Multiple choices; no
right/wrong way.

Post your results....a hyd thumb has doubled (at least) the usefulness of my hoe.

I agree. Its about what works best for you and what you are comfortable with (and not breaking stuff along the way) rather than a "perfect setup". My conversion is the last one in the above link. Will it work for everyone? No but it works quite well for me.