Homemade Articulated Mechanical Thumb

[3RRL]

Personally, I think teeth in general are over-rated, but it sure looks meaner!

I had my Gen 2 Thumb cut with some teeth, since the CNC plasma cutter
cost was the same. I had very little slippage with my Gen 1 thumb, and it
had no teeth, except for the two bkt teeth at the end.

I have a question on your linkage: why do you want one link to have
a pivot in the middle? It is not necessary, and that link will be weaker.
Why not have all 3 links pivot on the same pin?

LOL ... Yeah, it does look pretty cool if that means anything.
Regarding why I did not put all 3 links to the same pivot pin...
I thought about that a lot when I designed this linkage and it is necessary for what I wanted the jaw to do.

On my linkage, that one pivot is not in the middle but closer to where it attachés to the dipper stick. The big reason is that I can multiply the movement of the jaw vs the movement of the kidney link on the hoe, which powers the whole articulated mess. Since the middle attachment has a smaller radius than at the end, I am accelerating the jaw movement vs the movement of the kidney link sort of like a cam. That way I make the jaw close faster than the bucket is closing. By attaching all the links at the same point, I can only pull the jaw forward the same amount the little radius on the kidney link moves. Not only would I be limited to the travel of the kidney link, but they will close at the same speed. That would require quite a bit of bucket curl and the jaw might not get close enough to the bucket with the jaw back, out of the way. So yes, I've sacrificed some strength to gain that acceleration feature.

Now, I could do as you suggested, but that would mean having the jaw at a starting gap much closer to the bucket and not folded all the way back to the dipper stick....more like how you would position a "fixed" thumb. One of my thoughts was when using the backhoe for regular digging, the jaw would remain clear until the bucket was curled and then the jaw would rush up to meet the dirt and keep it from falling out. That way I might not even need to take it off into the "rest" position. I'm not sure how that will work but I'm going to try it out that way. If it doesn't work too good or gets in the way, I'll bolt it into the "rest" position.
Let me know if all that made sense or not.
Thanks,

 

[scott_vt]

Mornin Rob,
Nice project as usual ! Waiting anxiously for the finished product and results !

BTW, did you notice how Eddie gravitated towards this thread as soon as you started posting CAD drawings !

 

[KentT]

One of my thoughts was when using the backhoe for regular digging, the jaw would remain clear until the bucket was curled and then the jaw would rush up to meet the dirt and keep it from falling out. That way I might not even need to take it off into the "rest" position. I'm not sure how that will work but I'm going to try it out that way. If it doesn't work too good or gets in the way, I'll bolt it into the "rest" position.
Let me know if all that made sense or not.
Thanks,

Once caution -- don't use the thumb when digging in wet, sticky stuff like clay, or you might pack it into the bucket so tight that you have to stop and dig it out the bucket...

My bucket tends to "clog full" when digging in wet clay, regardless...

 

[BobRip]

Bob,
Thanks for sharing those photos.
I see that the one you made is a "stationary" thumb with adjustable positions for working and a neat fold away position. Is that right?

Exactly. You can also loosen the bolts and slide the thumb assembly for a course adjustment. Also it can be completely removed.

 

[3RRL]

Thanks for the replies guys.
Ken, I didn't think about packing the bucket that I might have to dig it out. My soil is mostly decomposed granite, and very little clay bit I'll keep that tip in mind.

Scotty, you are gonna have to wait a while before I get it mounted because we don't have a trip scheduled until the end of January. Best I can do is get it painted here at home and take a few more pictures for now.

I think I'll add that second row of shark's teeth to the plates across the middle to grab little stuff better. My buddy Larry (Gugloils) suggested it would help that way. Plus they look pretty cool in there.

 

[toolaholic]

3rrl great job. I have posted on my thumb project . Only have the steel, and no time yet. If You google Smart thumb, you will get some live action thumbs at work. Like Eddie I have a full size extendahoe,. when you extend the hoe you rotate the thumb! NOT FIXED.

 

[3RRL]

3rrl great job. I have posted on my thumb project . Only have the steel, and no time yet. If You google Smart thumb, you will get some live action thumbs at work. Like Eddie I have a full size extendahoe,. when you extend the hoe you rotate the thumb! NOT FIXED.

Thank you,
I can't wait to see your project come to life. We need lots of pictures so we can see how yours works. I wish I had an extendahoe too! There have been times when I wished my Nardi was bigger. And the extra reach is really cool.
PS
I started painting the links and jaws but don't have pics yet.
I added the extra rows of teeth too. They look good.

 

[3RRL]

OK,
I had a chance to weld the extra rows of teeth to the inner plates. I had to machine the height down a little so they would not stick up above the outer teeth. They came out pretty cool looking. I also primed and painted the jaws and linkage and bolted everything together. I used Ø3/4" hardened shoulder bolts and Nylock nuts and hardened washers for spacing. I have it mocked up sort of like what it will look like once it's mounted to the dipper stick. Never mind the unpainted bars, they are there only so I could prop it up.

The front white pieces will be welded to the dipper stick, under it and about 4" away from the bucket pivot. The middle white round pieces will be welded to the moving kidney shaped arm (attached to the hydraulic cylinder) which powers the linkage. And the back white round pieces will be welded to the side of the dipper stick.

Here is what it looks like now:





What do you think so far?
I'll try to go up this weekend and attach it, if Loretta can get off work.
Otherwise we'll have to wait another week.

 

[dfkrug]

Wow, that's HUGE. Nice red paint, too.

Looks like your main thumb link is about 1-in x 2-in?

I look forward to seeing how it articulates....maybe you will
post a small WAV file?

I just got a new bigger drill press so I can have an easier time with
my 1" holes. Moving toward MT3 tapered bits and a wet table.

 

[3RRL]

Thanks Dave,
That main link is 1" x 1.5" You have a great eye for stuff like that! That's also why I'm not too worried about the linkage being too weak, even the 1/2" x 2" links ... at least I hope so. If I ever get back up to the property and get that thing attached, I'll link a video of how it works.
Thanks for asking.

Your new "wet" drill press and MT3 tapered shanks will increase your capability. Much better than a smaller chuck set up. Try to get your rpm right around 125rpm ±10 for the 1" drill so you don't burn it up or work harden your piece. Smoke a ½" drill through there first. Coolant will definitely help....even air.
Good luck with the new drill press.