Custom hydraulic backhoe thumb

[MEMEMEME]

Your project looks wonderfully well thought-out and executed and I was hoping to just pick up the same valve you used for $50 and work out the construction details for my machine on my own.

My problem is [actually, one of MANY...]-I know precisely nothing about hydraulics other than how to rebuild cylinders, change hoses and how to remove/rebuild/replace the hoe valve stack on my old hoe.

The Hydraforce pdf makes my head want to explode...I probably just overlooked it, but I didn't see any explanation of the alphanumeric codes on these valves.

I live in a pretty remote area with no hydraulic supply outfit closer than 250 miles so I can't easily drop by and talk to the guys with the parts books and explain what I want and have them find what will work. No point in calling them up and trying to explain it because I don't understand it well enough myself yet.

My M.O. is usually to start collecting parts and pieces for a project whenever I find them really cheap and then build a few months later. Since I can't find the exact valve you used anywhere and the HydraForce supplier I contacted didn't even bother to reply I began haunting eBay for something similar. The valve I listed is on there for $40 which sounds pretty good to an old fart on Social Security-IF it can be made to work.

I can fabricate brackets and mounts and have several unused cylinders in various sizes which appear to be OK for this project but don't really want to have to take a mini course in hydraulic theory in order to build a thumb on the cheap.

This old hoe [which is 14 years younger than I am] only cost me maybe $4,500 total so far [manhours not included...] and I won't be doing more than picking rocks and building a couple of retaining walls and maybe grabbing the occasional log or pipe with the thumb, so extreme ease of use isn't a high priority.

Wiring the solenoid valve to an ignition-switched source seems to take care of any issue with draining the battery.

 

[MEMEMEME]

Well, I've FINALLY located a SV08-24-6T-N-12DS valve and it should be here next week. $62 plus shipping. A bit more than the $40 the OP mentioned back in '08-thank God there is no inflation in this country or it might've cost even more...ullinghair:

 

[Aquamoose]

Very interesting read, ongoing to do this over the winter on my BH76 backhoe on my Branson.

Question: Has anyone of you considered a mechanical diverted setup or is it too cumbersome? I have room to run extra lines back to the controls where I will install the diverter as I'd like to keep it out of the way.

Hat tip to you fellas,

 

[bumperm]

Aquamoose,

Considered, but just as quickly discarded. If you are paralleling the bucket cylinder to drive the thumb, then the discussed solenoid valve has some real advantages, the least of which is that running a pair of wires is easier than running hoses.

The biggest advantage, at least on my BH77 (and I assume it's pretty much the same as your 76) is the operator's control for the thumb. In use, the thumb is far from the set it and forget it operation that would be suggested coming from a mechanical thumb, where positioning the thumb and making do with it in one spot is the only practical, but sometimes frustrating, way to go - - unless you enjoy jumping on and off the tractor a lot. When you have remote control of the thumb you will find that you are moving it often enough so it needs to be easily accessible. And preferably not having to take your hand off the joy sticks. That leaves either foot control (and there's not enough room for my long legs and big feet to be doing that. Or:



Momentary push button switch for thumb hydraulic control.

 

[briandantz]

Guys,
Here is a Dfkrug and Bumperm hybrid I built last summer. this is the way to go. Time tested. Probably closer to the Bumperm design.
https://www.youtube.com/watch?v=lamu34e837I

 

[dfkrug]

Guys,
Here is a Dfkrug and Bumperm hybrid I built last summer. this is the way to go. Time tested. Probably closer
to the Bumperm design.

Looks good, Brian. How did you deviate from my design? If you set up your switch to have a position
that allows for a momentary button on the joystick, then you will be like both of our designs.

 

[bumperm]

Brian,

I do like the way you ran the hose for the thumb cylinder up alongside the curl cylinder - more out of harms way than doing the S turn loop thing I did.

However, I made a change on mine since it slid off the ways. Moved the solenoid valve more out of harm's way, added a short welded extension to the cylinder to make use of it's full range (the retracted length needed to be about 1/2" longer, so the extension also allowed more thumb reach. And while I was at it, I rotated the cylinder sleeve to have better access to the zerk fitting.

Where you have your valve is where mine was - I smacked it pushing over saplings and working in brush.

New valve position:

 

[Racerwannabe]

So after reading this forum multiple times, I said to myself, "This is something I HAVE to do". I just got a new Woods BH75 with the mechanical thumb and I can appreciate how useful a hydraulic conversion would be. But I've got a couple challenges that I'd love some expert input on, keeping in mind that I'm mechanically inclined but have little experience tearing into hydraulics.

1. Woods told me the curl cylinder is a 2 1/2", 3000# cylinder with a 12 1/2" stroke. I confirmed the stroke with a tape, and the OD of the cylinder body is a little over 3", so I tend to believe them. Figuring I have to approximately match the applied forces, I thought I'd go with the 2 1/2" Chief WX welded cylinder that has the rotating ports (which Bailey's reports as backordered). Interestingly, the 2 1/2" cylinders take 3/4" pins, while the 2" cylinders that you guys are using take the 1" pins. My thumb has 1" pins. What to do about this? Given this cylinder would only experience significant compressive forces, would I just hog out the ends to 1"? Or bush the bosses in the dipper and thumb and go with the 3/4" pins that the cylinder wants?

2. The pin-to-pin dimension on the existing thumb linkage is 20 1/2" in the stowed position. The retracted length of the 2 1/2" WX cylinder with a 12" stroke is 20". The thumb won't stow quite as tight against the dipper, but probably OK. The range of motion on the existing thumb linkage is 13", so I think I'll be OK with a 12" stroke. You guys with me on this? A cylinder with a 14" stroke has a retracted length of 22" which I think is too long to stow the thumb properly.

3. Now the plumbing. Below (I hope) is a photo of the dipper. The curl cylinder has 90 deg ports welded on. According to Woods, they take a SAE 6 male O-ring Boss fitting. The centerline of the female is only 3/4" off the surface of the cylinder. Can I get a male O-ring Boss tee in there? If I have to spin the tee to thread it in and then tighten the O-ring keeper nut (which is how I think they work), then the answer is NO. If the answer is no, then what? How would you plumb it? Short section of hose off the cylinder fitting and then a tee? Or two 45's to step off the surface of the cylinder? I think it might get real ugly real fast.

4. The part that I thought would be the most difficult turned out to be the easiest: I ordered the Hydraforce SV08-24-8T-12DS valve from Hydro-Air Hughes in CT. All pieces parts were in stock and it should be here on Monday. The 8T designation indicates SAE 8 ports, which I thought would be a good idea since the WX cylinder has SAE 8 ports as well. Would likely mount it like Bumpern did, provided I can still get to the grease fittings.

Looks like this will be a winter project since the cylinder is backordered. I'd prefer not to modify the new cylinder because it seems like the length and stroke will be "close enough". Plus I don't have the right tooling but I could call in a favor to have it done if I need to.

Any other potential issues here? Would really appreciate some fresh sets of eyes on this before I order a bunch of stuff that isn't going to work!

 

[bumperm]

Make sure the manual link bosses will provide enough spacing from the dipper boom to mount the cylinder you are talking about.

I'd use two 3/4 to 1" bosses to adapt down to the smaller 3/4 cylinder pin.

"2. The pin-to-pin dimension on the existing thumb linkage is 20 1/2" in the stowed position. The retracted length of the 2 1/2" WX cylinder with a 12" stroke is 20". The thumb won't stow quite as tight against the dipper, but probably OK. The range of motion on the existing thumb linkage is 13", so I think I'll be OK with a 12" stroke. You guys with me on this? A cylinder with a 14" stroke has a retracted length of 22" which I think is too long to stow the thumb properly."

If, as you say above, the mechanical linkage retracts to 20 1/2" and the cylinder retracts to 20", that would have the cylinder coming up short, not being able to retract all the way, banging the thumb into the cylinder, it would also subtract an additional 1/2" from the effective extended length - if I'm understanding you correctly.

Okay, I wouldn't necessarily go by the length of your mechanical linkage unless, that is, it allows full thumb movement in the extended position as well. It is desirable to have it all, full retraction and full extension, if you can get that. I got more extension with the cylinder I used, but that's on a different hoe of course. In order to fully utilize the range of the cylinder, I added a 1/2" spacer to the cylinder end by cutting off the pin boss, inserting the spacer and welding it back up. This also allowed me to correct a small alignment issue, tack welding the spacer in place while mounted to the hoe, then taking it off to fully weld. Also gave me the opportunity to move the zerk fitting so it wouldn't require disassembly just to grease the darn thing.

You are correct on the SAE O-ring issue, you gotta have room to swing the thing to thread it in, ending in the direction you want the fitting aligned, then snug up the nut driving the washer to seal and lock.

I know I haven't addressed all the issues . . . need more pictures and I need more active brain cells.

 

[Racerwannabe]

Thanks Bump: "If, as you say above, the mechanical linkage retracts to 20 1/2" and the cylinder retracts to 20", that would have the cylinder coming up short, not being able to retract all the way, banging the thumb into the cylinder, it would also subtract an additional 1/2" from the effective extended length - if I'm understanding you correctly."

You are absolutely correct - I had it backwards. This is an important point!

The photo shows the thumb linkage fully extended which is 33 1/2" pin to pin. The 2 1/2" WX cylinder with a 12" stroke gets me to an extended pin-to-pin of 20" + 12" = 32". This is an inch shorter than the mechanical linkage. Now I get why you added a 1/2" weld-in spacer. I could do the same and get my retracted length up from 20" to 20 1/2" (matching the mechanical linkage) AND get my fully extended pin-to-pin dimension up to 32 1/2". 1" shy of full pin-to-pin extension with the mechanical linkage.

Now I'm curious whether a cylinder with a 14" stroke would work. I'd sacrifice some stowage because the retracted length is 22" instead of 20". Time to get the tape measure out again! Looks like the "ideal" cylinder is right between the 12" and 14" standard stroke sizes, both for range of motion and retracted length.

How tight does your thumb tuck up to the boom and how far does it extend? Does it look anything like mine when fully extended?

I think I'm good on the pin boss on the dipper. The centerline of the pin is 2" off the dipper. This should leave me with 1/2" of clearance using a 3" OD cylinder.

I'm still a little worried about the 3/4" pins given the forces involved. I have 3 7/8" clear between the pin bosses on the thumb. The rod end is 1 3/8", so I would need two 1 1/4" bushings to take up the slop. Bailey told me the cylinder could generate 9300 lb of force at 1900 psi. I don't know if a 3/4" pin is going to withstand that without bending?

And I took a closer look at the bucket linkage. Turns out the curl cylinder linkage pin is 5 1/2" from the pin the bucket rotates on, while the (future) thumb rod end pin is 7" from the pin the bucket rotates on. So the thumb cylinder would impart more leverage on the thumb than the curl cylinder does on the bucket. Makes me wonder if I could get away with a 2" cylinder instead of a 2 1/2" for the thumb. We are trying to match bucket curl and thumb rotation forces, correct?:confused2: