Custom hydraulic backhoe thumb

[IslandTractor]

Nice job. I have to get around to doing this on my Woods BH-90x. I have a mechanical thumb but find it next to useless so I don't use it. I could definitely use the hydraulic version though.

 

[MEA]

MEA,

The valve is a Hydraforce SV08-24-6T-N-12DS

As mentioned earlier, I tried to order direct from Hydraforce, but no joy. They referred me to one of their dealers Hydraulic Controls in the S.F. Bay area 510-658-8300, who referred me to their branch in Yuba City, CA (closer to me). Called them and it wasn't in stock, 3 week wait and I flew over to Sutter County airport and they met me there with the parts!

Hydraulic Controls, I think, has outlets all over, so you might could find one close to you.

I used two 3/8 JIC female 1/4 inch hoses, one 24" and one 18" (stock lengths) from surpluscenter.com/Hydraulics/

I bought all the hydraulic fittings from Discount Hydraulic Hose

One particular part, the SAE 8 O-ring to SAE 6 O-ring 90 degree, I could only find at discount hydraulic hose:

O-Ring Boss (ORB) Union 90ｰ Elbow part 6807-08-06

This goes from the cylinder (assuming you use the same one I am using, as it has SAE 8 O-ring flush ports) and the hydraforce valve has SAE6 ports. This fitting allows the valve to fit nice and snug (snugger than what I've shown in my pics - as this particular fitting was out of stock so I used two fittings to "get there"). I have the right one now and will install it when I lengthen my cylinder a little. (OCD . . . the cylinder works as is, I just can't leave good enough alone - it's a sickness :c).

BTW, you will be replacing the 3/8 JIC male to 1/4 NPT 90's on the BH77 cylinder with street T's 3/8 JIC 1/4 NPT

Plumbing is a piece of cake.

Oh, the switch I used is this'n: Amazon.com: Alpinetech 19mm 3/4" Waterproof Momentary Stainless Steel Metal Push Button Switch Screw Terminal Extended Button Normally Open 1NO: Automotive

bumper

Thank you , I will let you know how I make out.

 

[bumperm]

When swapping curl cylinder fittings, I used a step ladder to block up the dipper stick so the ram end of the curl cylinder was almost level (ram end a little higher), then removed the upper pin from the curl cylinder and used a wood blocks to keep that end of the cylinder higher. Relieve any pressure on curl cylinder with joystick. This is all necessary as otherwise there would be no room to install the street T fittings. Note when removing the original 90's, they are screwed in **** for tight - - I mean *seriously* tight. I had to use a large adjustable wrench to get enough leverage to break them loose. Pipe wrench would have worked too, but those were at the hangar.

Even w/ steps to get ends of cylinder higher and remove pressure, there will still be leakage of course. Car drip pan, garbage can lid, etc is helpful, along with lots of paper towels. Pre- teflon tape the new NPT threads before starting.

I purchased the anti-chafe hose sleeve from Amazon: Amazon.com: apache hose and belting inc 39020518 1.59 -Inch ID x 15 -Feet, Nylon Protective Hose Sleeve: Industrial & Scientific

best,

bumper

 

[dfkrug]

I have the right one now and will install it when I lengthen my cylinder a little.
(OCD . . . the cylinder works as is, I just can't leave good enough alone - it's a sickness :c).

Getting the cylinder length and stroke just right makes a big difference. I remember when I got
my first hyd toplink, an off-the-shelf unit. Worked OK, but when I went with a custom cyl with
the stroke and length optimized for my CUT and implements, it was much better. I hope
this thread shows that clearly.

Since the cylinder is harder to modify than the dipper bracket and the thumb itself, I would
encourge people wanting to make a hyd thumb to get a cyl that you DON"T modify, and
adapt the thumb and dipper bracket to IT.

 

[bumperm]

dfkrug,

No argument from me. But, you were fabricating your thumb from the get-go, so that has your approach making a lot of sense. For those adapting an existing manual thumb (Kubota sells only the manual thumb option for their BH77 hoe) it makes more sense to leave the mechanicals as is . . . the BH77 hoe comes with a nicely welded on and substantial upper thumb cylinder bracket, whether or not your order the thumb. Guess they figured it makes more sense to make all the dipper sticks the same.

Modifying the cylinder is both straightforward and easy enough if you have a metal cutting band saw, as all you need do is cut off the cylinder end tube. Insert a 1/2" spacer and reweld it. I did this when modifying an off-the-shelf cylinder for my TnT tilt (cut apart fixed support link and used the ends on the cylinder. I disassembled cylinder for welding, though wrapping with wet rags, could probably have gotten away with leaving it intact.



I took the tractor to the shop today with the intent of modifying the thumb cylinder. I thought it was maybe 1.5 inches too short. Actually, it's only 1/2" short. Now admittedly, that 1/2 inch translates into 4 inches of movement at the distal end of the thumb. So I decided I didn't have time to make the mod now, as it really doesn't buy me much. The cylinder I purchased is a good match for the BH77, and has the advantage of flush ports that can be adjusted circumferentially to exit where needed (cylinder end only two choices, 90 degrees apart). I'll run it like it is for now, and knowing me, probably still add the spacer one day - - maybe.

bumper

 

[dfkrug]

No argument from me. But, you were fabricating your thumb from the get-go, so that has your approach
making a lot of sense. For those adapting an existing manual thumb (Kubota sells only the manual thumb
option for their BH77 hoe) it makes more sense to leave the mechanicals as is . . .

Actually, I did not fabricate this hyd thumb using a new design from scratch. So I had to modify an
off-the-shelf cylinder for the correct stroke and closed length (see post #4). I had built up several
thumbs that fit my hoes, but were initially intended for mechanical use. The cylinder pivot point on
the thumb was fixed and I was not going to make another thumb to move it.

I understand that some folks will not want to design from scratch in order to keep from changing their
thumb or their existing dipper bracket. In starting this thread, it was my intent to show what I did,
but also talk about tradeoffs and suggest other approaches that may be easier.

But if someone wanted a hyd thumb and had not made any commitments, then I would suggest
making an off-the-shelf cylinder of the right diameter the "dependent variable", and the dipper
bracket position and the thumb pivot the "independent variables". I DO think that removing and
welding a new dipper bracket is easier than cyl mods.

 

[bumperm]

I DO think that removing and
welding a new dipper bracket is easier than cyl mods.

You are obviously very talented, no question . . . and your posts were a huge help to me in "hydraulicizing" my thumb. But, I disagree with your last contention, at least as it applies to the Kubota BH77 (and probably BH65), inasmuch as the upper thumb bracket is "seriously" welded to the dipper stick. To remove it would both risk destroying the bracket itself, which has welded in bosses for the pin, or compromising the integrity of the dipper stick if the removal effort was botched. This is exacerbated by the bracket being welded along both edges of the sides of the dipper stick, and then also across the recessed bottom of the dipper stick in a position that would be all but impossible to remove copious amounts of grinding. Also, to even consider thumb bracket relocation would mean the use of hand tools (electric or otherwise) though it would be "easier" if one remove the whole dipper stick. Okay, one could cut off just the sides of the bracket and then start over that way, but even that's more work than "adjusting" a cylinder's length or shortening its stroke.

Increasing the length of a hydraulic cylinder I find to be no problem, can be done in the generally recommended "disassemble first" method, or the "wrap it with wet rags and don't weld near the seals" method (some recommend filling with water first). Takes a little more work to decrease a cylinder's length, but if that was my only alternative, it's doable too. Both these options obviously require a modicum of welding and fabricating skill, and it's nice to have a machine tools as well.

bumper (with "hobby" machine shop)

 

[avc8130]

Are there any concerns with the flow rate limits of the solenoid valve you have chosen?

The SV08 is only rated for 4.5 gpm.

ac

 

[dfkrug]

Are there any concerns with the flow rate limits of the solenoid valve you have
chosen?
The SV08 is only rated for 4.5 gpm.

The short answer is no.

Remember that flow is shared with both cylinders when the valve is open. Of course, both
cylinders do not move at the same time usually, due to different loads.

Also, I do not run my hoe at the full engine RPM where I get my specced 8.3 GPM.

Finally, the flow rating from the manufacturer must make some account for duty cycle. Any
sustained flow that I subject it to will be for a few seconds at a time. I do not know
how Hydraforce rates their valves, but I am sure that it is rated for 4.5GPM over a longer
period, and it can tolerate momentary excursions into higher flow conditions.

Oh yeah, it has worked very well in the field for over 6 years.

 

[avc8130]

The short answer is no.

Remember that flow is shared with both cylinders when the valve is open. Of course, both
cylinders do not move at the same time usually, due to different loads.

Also, I do not run my hoe at the full engine RPM where I get my specced 8.3 GPM.

Finally, the flow rating from the manufacturer must make some account for duty cycle. Any
sustained flow that I subject it to will be for a few seconds at a time. I do not know
how Hydraforce rates their valves, but I am sure that it is rated for 4.5GPM over a longer
period, and it can tolerate momentary excursions into higher flow conditions.

Oh yeah, it has worked very well in the field for over 6 years.

Ok, just checking. I might choose the SV10 series just to have a little head room. My machine is rated at 11.8 GPM and the SV10 series is 10gpm.

ac