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  1. #1
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default another backhoe mechanical thumb, fixed or articulated

    Here is my 2nd generation home-made backhoe thumb, designed for
    my Prairie Dog 7.5 subframe-mounted hoe. I posted my 1st gen thumb
    last year as some may remember, for this same Woods 7500 clone.

    First, for you backhoe owners, a thumb of any kind will be a
    tremendous addition, at least doubling the usefulness of this already
    valuable attachment. A mechanically articulating thumb works way
    better than a fixed one, too.

    First photo is of my 1st Gen. I learned a lot from it, so I incorporated
    several design changes in the 2nd Gen. I considered going to a full
    hyd thumb, since I have used them before, but I do not like the
    exposed hoses on the outside of my hoe. Also, the work of plumbing in
    another spool valve (foot-operated) would be quite significant.

    2nd photo is of all the steel parts for the 2nd Gen. I paid a fab shop to
    use their CNC plasma cutter to cut the curved side pieces from my
    DXF file. The rest I made and welded (photo #3). Main pivot pin
    is 1", and the tip is a piece of plow steel. My 1st Gen used small
    backhoe teeth, and even those got quite worn picking rocks.

    Finally, #4 & #5 are the fixed thumb, using a std cat 1 adjustable toplink.
    Attached Images Attached Images

  2. #2
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Next is the articulated version of my Gen 2 thumb.

    For this project, I actually made a full scale mockup out of OSB, so
    I could plan the links and the extent of the articulation. Also, I had
    to use the existing 25mm pivot at the lower end of the curl cylinder.
    This sounds easy, but I needed an extra-long 25mm pin drilled for
    grease and a way to drill a 25mm hole in the new link. Also, pin
    rotation must be restricted, so a special pin had to be made. Links
    are 3/8" x 1.5".

    I took a 10 second video with my Nikon, but the file size is 3.2 MB.
    I have dialup, so I can not post. Even 5 sec would be 1.6MB. Instead,
    I am posting 4 series pix of the thumb articulating. I shortened up
    my Gen 2 a bit so it clears the main boom by an inch at full open.
    In use I find that I can switch from digging to grabbing very easily
    without having to adjust or remove the thumb. Sweet.

    Next modification will be to try a slave hyd cylinder, connected in
    parallel to the curl cylinder. That may work even better than the
    this method.
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  3. #3
    Super Member 3RRL's Avatar
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    Foothills of the Giant Sequoia's, California
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    55HP 4WD KAMA 554 and 4 x 4 Jinma 284

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Dave,
    Thanks for taking the time to show us you Gen 2 stationary and articulating thumb. I think they came out great. It's funny you and I were working on similar projects, not knowing exactly how the other's would look.
    Our concepts to power the jaws are the same except you used different pivot points than I did.





    The other difference is your linkage runs above the dipper stick and mine runs below it.





    Your final link to the jaw seems to be a lot longer than mine. How long is that one? Are the main set of pivots connected to each other (where all 3 links come together) or to the cylinder? Do you have a "rest" position for your thumb?
    Very interesting indeed, how we accomplished the same thing with the same concept but varying technique. It's great to be an American, isn't it?
    Great job.
    Last edited by 3RRL; 02-07-2007 at 09:34 PM.
    Rob-
    ...The Older I get...the Better I Used to be...
    Member of the Month

  4. #4
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: another backhoe mechanical thumb, fixed or articulated

    You beat me to it, Rob. Not that anyone is competing. :-)
    Thx for the support.

    To ans your ?, my longest link is prob over 2 ft, I don't recall.
    The thumb moves extra-fast when nearly closed, as the angle
    betw link and thumb gets quite acute. I am not sure about what
    you mean by a resting place...you mean disconnect it? If so,
    no, there is none with out pulling links. I found that with the
    Gen 1 thumb, I dug with it in place, too, rather than getting
    off my lazy a55 and removing it. It even came off in 5 seconds. I did
    find the thumb actually assists in digging. Much more so with
    Gen 2, so I do not anticipate disconnecting it. I have too many
    rocks here anyway.

    I tried different kinds of pin retainers this time. Anything exposed on
    the sides of the thumb will be destroyed, as you will find.

    I did not even consider a link in the middle of my kidney link, as you did,
    since mine are cast and have large concavities on their outboard sides. I
    also did not want to weaken them, esp since they are cast steel.

    I never considered hanging most of my linkage below the dipper as you
    did, since that is where most of the "dirt action" is.

    I am about to order some more toplink cyls, so I will get to try my
    4th type of thumb soon.

  5. #5
    Super Member 3RRL's Avatar
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    55HP 4WD KAMA 554 and 4 x 4 Jinma 284

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Dave,
    I like that your linkage is above the dipper stick, out of the way. I should have considered that in my design. But at the time, I was not sure if it would be useful for digging...mostly "grabbing" stuff.
    I am not sure about what
    you mean by a resting place...you mean disconnect it? If so,
    no, there is none with out pulling links. I found that with the
    Gen 1 thumb, I dug with it in place, too, rather than getting
    off my lazy a55 and removing it. It even came off in 5 seconds. I did
    find the thumb actually assists in digging.

    So that is good to know that it assists in digging. I have not tried mine out yet and I'm keeping my fingers crossed, hoping for the same results.
    Yes, by "resting place" I meant a spot for it to fold back when not in use. But heck, if it comes off in 5 seconds, that is even better. Mine will need a few minutes to remove some bolts.
    It's too bad you can't load up that video, I would live to see that thing work. But from your pictures, I saw how fast the jaw closes as it gets closer to the bucket.
    Very cool Dave.
    Rob-
    ...The Older I get...the Better I Used to be...
    Member of the Month

  6. #6
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Don't know if I was clear. My 1st Gen thumb came off quickly,
    but my 2nd Gen does not come off quite as fast. I do not anticipate
    having to take off Gen 2 at all. On the Gen 1 thumb I welded
    handles onto the main pivot pin so it would be faster to remove. That
    got all bent up in use. I still have to pull the main pin and one other
    to remove the thumb and a pliers is needed to grab the hairpins. Maybe
    30 sec to one minute to remove if the pliers is handy.

    In hardcore digging, I am not able to fully curl the bkt with the thumb on,
    but I seem to hit 50 lb rocks every 6-in of digging.

  7. #7
    Veteran Member
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    lower part of Md.
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    JD310, ASV RC-100

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Yes, they are both VERY cool add-ons. Different horses of a different color and all that.

    We want real action shots of how the stupid things really work though Quit teasing us and get to it!

  8. #8
    Super Star Member EddieWalker's Avatar
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    Several, all used and abused.

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Quote Originally Posted by dfkrug
    To ans your ?, my longest link is prob over 2 ft, I don't recall.
    Your thumb is similar to what I put on the front bucket of my loader. Same principle and the linkage looks more like what I did than Robs. One thing that I didn't expect was how much preasure is on the linkage that closes the thumb. I used half inch by 4 inch steel and assumed it could handle it.

    I was wrong and learned that almost the first time I used it. The first picture shows how it bent. Looking back, it was obvious that I vastly under-estimated how much force is aplied when closing the thumbs. Once the thumb locked the logs in place, the hydraulics were able to just bend and twist the metal like it was nothing.

    In the second picture, you can see how I put 3/8 by 2 inch steel on top and bottom of the 4 inch steel to create an I-Beam of sorts. Lots of welding, but after using it for about 100 hours, it's holding strong.

    The last picture shows me carrying the top part of a pine tree with it. I can pick up more weight, but balancing it is just about impossible. Most big trees I cut in half, or if they are realy big, I cut off the root ball, then cut the rest in half before moving them. It's turned out to be more sueful than I'd hoped and I'm really using it allot lately clearing up my land and burning.

    Thanks for sharing your progress and the great pictures!!!!

    Eddie
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  9. #9
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Eddie, it is very true that you must be very carefull when
    putting any plain strap in length-wise compression, as you
    found out. Your industrial tractor's curl force is HUGE.
    My longest link does experience significant compression, but
    I tested it to see if it could take it, fully prepared to have to
    strengthen it. So far, so good.

    Let's see more of your pix!

  10. #10
    Gold Member dtd24's Avatar
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    Schenectady, NY
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    98 JD 1070

    Default Re: another backhoe mechanical thumb, fixed or articulated

    Nice, I like the use of original motion. I have thought about a stationary thumb, but working on FEL grapple projects now with some of your help. 3RRL now your hoe will match the FEL..........very nice.
    98 JD 1070 (573 hrs), 440 JD Loader, 8B JD Back Hoe, 5' King Kutter Rotary Cutter, 6' King Kutter Landscape Rake, 7' King Kutter Back Blade, 6' Farm Force Box Blade, Custom Design/Built Grapple, Farm Force PHD w/ 9" & 12" Augers

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