Homemade Articulated Mechanical Thumb

[tlbuser]

I can paint them too.

????? Seems like the last "special project" had a dedicated painter. What did you do wrong to make her unavailable for future jobs?

This project is turning out great so far. Kind of a hard way to "cut teeth" though. I really like your v-block setup.

 

[3RRL]

Thanks again guys,
K7147,
Of course proof is in the pudding so I need to get it done and welded to the backhoe to try it out. I'll probably post a video and some photos. (If it works )
You know Eddie,
There is nothing like a bigger hammer if all else fails. LOL ... I've got a couple big ones in my tool boxes too....I'm not exempt from Murphy's Law either.
tlbuser,
Well, I'm hoping I've been good and she will do it again for me. I've got to get the parts welded and cleaned and then she will do her magic.

I do have some concerns as to what 63DH8 said:
I used to work for an outfit that designed and built bucket thumbs. Unless you use a common pivot point, whatever you are carrying will "roll" in the thumb/bucket. Use your CAD to roll the bucket and thumb. You'll see how the thumb will be closer and further away as you roll the bucket. Our boss tried to get us designers to make a thumb that was prebuilt that would be welded onto the stick (excavator arm), but it wouldn't work due to the rolling effect. That made grabbing then rolling out the bucket impossible to do without dropping what was carried.
I used the CAD to move the linkage and bucket from the pivot points in the picture in one of the first posts where there are multiple drawings of it.
You can clearly see how the bucket and jaws are approaching each other.



It seemed to me the bucket and jaws approach each other to "grab" stuff. Does anyone see a problem where if I "curl" the bucket to grab something it will drop out? I've welded 2 plates across the jaws to help with stability and to catch stuff.



Maybe I should add some extra teeth on the plates ... kind of like a sharks mouth? I do have those drilled out remnants I could cut up and weld to them.
Sort of like this, except I would make the rear ones lower profile. Or do you think adding them makes no sense and could just collect dirt? It does look pretty cool though?



I'm worried I missed something here? I do realize the thumb pivot is about 4" away from the bucket pivot. I guess what he is saying if the object I pick up is smaller than 4" it could "roll" up the thumb towards the gap between them. But then again, I wasn't planning on using the backhoe for stuff THAT small. More like basketball or beach ball sized stuff.

If anyone has any input on this I would appreciate it.
Thanks,

 

[EddieWalker]

You can clearly see how the bucket and jaws are approaching each other.



It seemed to me the bucket and jaws approach each other to "grab" stuff. Does anyone see a problem where if I "curl" the bucket to grab something it will drop out?

I've never done this, so it could just be that I don't understand it, but wouldn't it be better for the bucket and the grapple to come together at the very bottom position?

I understand that with a fixed thumb, you have to bring the material to the thumb, then trap it together, but if you didn't have to do it that way, why would you?

I don't see how it would matter too much with big objects to pick up, but smaller stuff, like a hundred or two hundred pound rock that is maybe more flat than tall.

Of course, maybe it doesn't matter. Maybe you just push the object to the thumb.

Thanks, this is very interesting.

Eddie

 

[KentT]

I've never done this, so it could just be that I don't understand it, but wouldn't it be better for the bucket and the grapple to come together at the very bottom position?

I understand that with a fixed thumb, you have to bring the material to the thumb, then trap it together, but if you didn't have to do it that way, why would you?

I don't see how it would matter too much with big objects to pick up, but smaller stuff, like a hundred or two hundred pound rock that is maybe more flat than tall.

Of course, maybe it doesn't matter. Maybe you just push the object to the thumb.

Thanks, this is very interesting.

Eddie

Eddie, I find myself using the fixed thumb in exactly the opposite way -- I position the thumb first, then curl the bucket to clamp the material against the thumb.

This picture of the excavator pulling stumps on my lot shows what I'm talking about. He positioned the fixed thumb against the stump, then pinched, then lifted...

http://www.loonlanding.info/Img_0895.jpg

http://www.loonlanding.info/Img_0898.jpg

He pulled the stumps, not pushed them out, nor dug them out... He'd first push hard with the thumb, then pinched the stump, then curled back as he lifted... the pine stumps would just "pop out"...

Watching how well this worked, I bought a thumb and installed it on my mini-hoe... totally different scale, but I can pull out 2-2.5" saplings if the soil is moist...

 

[dfkrug]

Thanks again guys,
K7147,
Of course proof is in the pudding so I need to get it done and welded to the backhoe to try it out. I'll probably post a video and some photos. (If it works )
You know Eddie,
There is nothing like a bigger hammer if all else fails. LOL ... I've got a couple big ones in my tool boxes too....I'm not exempt from Murphy's Law either.
tlbuser,
Well, I'm hoping I've been good and she will do it again for me. I've got to get the parts welded and cleaned and then she will do her magic.

I do have some concerns as to what 63DH8 said:
I used to work for an outfit that designed and built bucket thumbs. Unless you use a common pivot point, whatever you are carrying will "roll" in the thumb/bucket. Use your CAD to roll the bucket and thumb. You'll see how the thumb will be closer and further away as you roll the bucket. Our boss tried to get us designers to make a thumb that was prebuilt that would be welded onto the stick (excavator arm), but it wouldn't work due to the rolling effect. That made grabbing then rolling out the bucket impossible to do without dropping what was carried.
I used the CAD to move the linkage and bucket from the pivot points in the picture in one of the first posts where there are multiple drawings of it.
You can clearly see how the bucket and jaws are approaching each other.



It seemed to me the bucket and jaws approach each other to "grab" stuff. Does anyone see a problem where if I "curl" the bucket to grab something it will drop out? I've welded 2 plates across the jaws to help with stability and to catch stuff.



Maybe I should add some extra teeth on the plates ... kind of like a sharks mouth? I do have those drilled out remnants I could cut up and weld to them.
Sort of like this, except I would make the rear ones lower profile. Or do you think adding them makes no sense and could just collect dirt? It does look pretty cool though?



I'm worried I missed something here? I do realize the thumb pivot is about 4" away from the bucket pivot. I guess what he is saying if the object I pick up is smaller than 4" it could "roll" up the thumb towards the gap between them. But then again, I wasn't planning on using the backhoe for stuff THAT small. More like basketball or beach ball sized stuff.

If anyone has any input on this I would appreciate it.
Thanks,

Rob:

Great CAD drawings and milling machine work, as usual. I recently
completed my 2nd generation thumb, and I built articulating linkages
as well. One link in my design uses the same pin as my curl cylinder,
and that has kept me from connecting it all up. (I do not have a 25mm
drill bit yet.) I also have to turn down some 1-in stock to make an
extra-long 25mm pin.

I took the old-fashioned approach and built a full scale wood mockup
first. I do not see a problem with NOT using the bkt pivot for the
thumb pivot as I never had any "rolling" action with grasped rocks or
logs. I am sure you will post a movie when yours is working.

The 2nd time around for me I had a shop in El Monte take my DXF file
and cut a bunch of the curved parts for me on their CNC plasma cutter.
It was quite reasonable. Cutting 1/2" plate is slow and tedious for me.
You guys in Socal have all the good deals on steel and machine shops!

I am sticking with the use of hard steel for the tip of the thumb as
my prototype used std small bkt teeth and got quite worn in normal
use, esp with rocks. I used plow steel this time.

 

[3RRL]

KentT,
That is one big excavator with a lot of power. My backhoe is a dink compared to that.
Thanks for sharing those pictures.

Eddie, your first question about coming together at the bottom is that I can only open the bucket back so far. In the position I have the dipper stick drawn, it is pointing down. This position is very much like the excavator in Kent's 2nd picture.

I hope I can explain this so it is not confusing, so bear with me...
Now when you extend the dipper stick out, more parallel to the ground, then the thumb would be more vertical to the ground and perpendicular to the dipper stick. That's also why I have several linkage connections. This is so I can vary the starting position of the thumb. In other words, if I set the thumb closer to the bucket, they will come together sooner, so the bucket has less curl before the two meet. If I set the thumb all the way back like in the drawing, that allows the bucket to curl quite a ways before they meet.

The reason for the different linkage positions is so I can (to a degree) set up the thumb for the type of grabbing I want to do. If I'm going to pick up rocks down a slope, I'll most likely have the boom and dipper stick extended straight out down that slope. So I would want to have the thumb set back like in the drawing so when the dipper stick is parallel to the slope, the bucket and jaws are in the correct position to grab a rock on the slope.

If I was grabbing rocks say from a level position, like from a road and the pile is a little closer to the tractor, then the boom and dipper stick would be more folded. In that case, I'd set the jaws closer to the bucket and the bucket fully extended out.
More like this drawing that shows the thumb starting much closer to the bucket.



The gap is a lot smaller to start with and they would clamp a rock a lot sooner. But that way I could pick up rocks with the boom and dipper stick more folded, which is the position you were referring to. Again, the dipper stick is drawn almost straight up and down here and I would probably not have the rocks that close to the tractor.
Does that make sense, I hope?

That drawing is just an example of moving the jaw closer to the bucket but in my linkage, I will not have quite that much adjustment. With a fixed thumb you can do that easily by having different locations to fix the jaws or some guys use a turnbuckle top link for that. My friend Dave Krug uses the turnbuckle style support.

 

[3RRL]

Hi Dave,
We must have cross posted as you see I referred to you in my last post.
Thanks for the compliments too.
One link in my design uses the same pin as my curl cylinder,
and that has kept me from connecting it all up. (I do not have a 25mm
drill bit yet.) I also have to turn down some 1-in stock to make an
extra-long 25mm pin.

I know what you mean and I thought about using the same pivot as the bucket but I did not want to make a metric hardened extra long shoulder bolt with 22mm threads on it.
That's also good information about using hard steel ... I thought about case and carburize the HRS for the jaws but would like to try them out first. I might flame harden them at the property?
Get more pictures of your 2nd generation thumb for all of us to see. It looks pretty cool! You know El Monte is right next door to me. If you need some knick knacks turned or milled, give me a holler.

 

[3RRL]

Any comments about adding the extra rows of sharks teeth to the center plates?
Yea or nay?

 

[EddieWalker]

Thanks Rob, that makes sense.

It's a great project and I'm looking forward to seeing it in action!!!

Eddie

 

[dfkrug]

Any comments about adding the extra rows of sharks teeth to the center plates?
Yea or nay?

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?

 

[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.