Hydraulic thumb

[ridefst]

Here's some drawings for a hydraulic thumb I'm working on.
All laser cut 1/2" steel (good to have friends)
2" x 16" cylinder
1" pins throughout, also using three pins welded in to space/strengthen the tips. No bracing in the bottom half of the thumb, so the cylinder will fit in the middle when I'm not using it.
Mostly want the thumb to handle that pile of firewood logs in the background.
I've got the hoe to install a bunch of drain tile in the back yard and pasture.

Doesn't seem to be any real good way to design this, unless I'd go for a common pin with the bucket (which seems like too much trouble). Since it's just logs, I'm not too worried about precise control of the tips to the bucket teeth or anything, so I think this'll be okay.

Already got the aux hydraulic lines to the boom, so I should just need to cut/weld this up, and run some short lines.

See anything I'm missing or screwed up?

 

[magicheater]

Something looks out of scale on your drawings. seems like the thumb is awfully long. Most I have seen are shorter but maybe you are on to something. Good luck with your project.

 

[CurlyDave]

If you can get a close look at a commercial hydraulic thumb for your machine, take some measurements, some pix, and then copy it.

There is a lot involved in getting just the right geometry, cylinder sizes, etc. A copy of a known good one would be your safest bet.

 

[ridefst]

I agree that it is kinda long, mainly due to the pivot point being a little far up on the stick.
I'll probably cut out a paper/cardboard version before cutting steel, maybe I'll be able to move the pivot down a bit. That'd help with the geometry overall anyways.

Not sure where to find a weld-on thumb around here. The local rental shop has a couple with the common-pin mount, but that doesn't really help me much.

 

[mwb]

I think the bucket curl will buckle the thumb cylinder. If the three pins (two cylinder, on thumb) are almost in line then you will not have any mechanical advantage to oppose the bucket curl cylinder. You might want to look at the curling force of the bucket and work backwards make sure the thumb and cylinder can handle it.

Here is a sketch that might help illustrate this. I moved the rod end pivot point out this gives the thumb cylinder some leverage. If the lever distance is shorter (than the bucket) then you will probably have to increase the cylinder size or risk busting it.

Does this make sense?

 

[ridefst]

Makes perfect sense, I'll have to make this change.
The downside is that it will not "store" as nicely when I'm not using it, but if I can make it shorter, it might stay out of the way anyways.
I should've noticed that when drawing, but I was focused on making it fold up as small as possible, rather than actually functioning well:ashamed:

Guess that's why I posted it up, thanks for the catch!

 

[sizzami]

just a thought , but I built one once for this guy who had me make it just short enough to fit in the bucket far enough so that he could use it to bust tops and brush.

 

[niemeyjt]

Have you thought about not having the thumb hydraulic - like the grip talon shown here:

Excavator attachments, Ripper Teeth, Clay Spades, Tilt Ditchers, Land clearance rakes, Grapples, Grip Talons

Some of what they are showing looks similar to your requirements.

It swings out of the way when not required.

J

 

[ridefst]

I did originally think about a fixed thumb, but figured that if I can make it hydraulic for only about $200 extra, then why not?

Not sure about making the thumb significantly shorter than the bucket, I can see the advantage if you want to "bite" something off, but I don't think that is right for me.

I certainly appreciate all the input though:thumbsup:

 

[dfkrug]

Not sure about making the thumb significantly shorter than the bucket, I can see the advantage if you want to "bite" something off, but I don't think that is right for me.

RE the length of the thumb.....you may want to make it short enough
not to hit the boom when it is perpendicular to the dipper. I made mine
just long enough to clear the boom, minus about 1/2".

MWB is correct that if your thumb cyl stroke it long enough to extend the
thumb out straight, you risk overpowering it with the bkt curl force. You
can avoid that by limiting the extend stroke of your cylinder, keeping the
retract stroke long enough so that the thumb is up against the dipper
when retracted.

Another thing to consider: when using weld-on thumb pivot backets at
the end of the dipper, you must allow for the extreme tension forces
pulling on the dipper stick. The metal is not usually thick there. My solution
was to wrap the bracket around the dipper before welding.

 

[ridefst]

Well, looks like all the concern about the thumb length was absolutely correct.:ashamed:

I decided to cut the pieces out of cardboard to mock it up, since I was having a hard time figuring out an exact mounting point on the computer.
Laser cut everything out of 1/4" thick cardboard and doubled them up to make everything 1/2" thick to match the steel.

Definitely looks pretty funny on there, I can probably take off 6-8" no problem.
I'm also going to look into designing it to use a hydraulic cylinder, but just putting a fixed link in to start with. If it works fine, then I just saved some money, and if not I can just buy the cylinder and drop it in.

Pics attached of making the cardboard version, and mounting it on the hoe.

Now, what can I do with these nice looking cardboard jaws? Keep 'em until Halloween?

 

[CurlyDave]

Keep 'em until Halloween?

Make a cardboard alligator now.

 

[andymil]

It seems like most of the fixed thumbs I see are about the same length of the bucket and teeth, and set up at about 90 degrees to the dipper arm.

If the thumb is movable and the pivot is anywhere but the bucket pivot pin, the end of the thumb will hit the bucket at different points depending on the amount of bucket rotation. Your cardboard mock-up seems to verify this.

 

[ridefst]

Yeah, I knew that the "close point" would vary because of the two different pivot points, but thought that it would be best to make it just reach at full extension, and overlap a bit the rest of the way.
However, it overlaps a whole lot and just looks plain goofy, so that's not gonna cut it

Kinda rethinking the whole hydraulic thing now, because I can't see how to make it really work that well, I'm probably going to just drop that idea entirely.

Think I'll just make it semi-fixed by using a Cat 2 toplink (cause I already have an extra) and let it go at that.

Additionally, the only reason to make the thumb move out to contact the bucket when wide open, is to pick up far away objects with the thumb underneath and the bucket on top (make sense?). This seems like a poor way to use the machine anyways, as the bucket is the strong point and the thumb should just provide pressure to hold, not actually support the full weight.
Conclusion: not only do I not need it, I shouldn't even want it!

Anyways, now I'm down to about a 23" long thumb overall. Still 1/2" steel, still welding a couple of 1" pins in between the two halves for strength/etc.

Look better now?

 

[andymil]

Kinda rethinking the whole hydraulic thing now, because I can't see how to make it really work that well, I'm probably going to just drop that idea entirely.

I read on one of the forums about plumbing the thumb cylinder in parallel with the bucket cylinder by putting a tee in the lines for the bucket cylinder and using a manual valve to stop the flow to the thumb when you're not using it. With the valve open, both will move at the same time, but the one encountering the least resistance will move first. If the bucket hits the object first, it will stop and then the thumb will move until it contacts the object and pinches it.

It might be a little tricky to use but you wouldn't need a separate valve and another set of hoses running out to the dipper. It might be more versatile than a fixed thumb.

 

[Topstrap]

Your design looks almost identical to what I made for my Yanmar. I started out thinking I'd just make one with a stiffarm but then decided to go ahead and add hydraulics to it. Added a valve to my blade circuit that I can lift and then use the thumb but am thinking about changing it this summer to use my foot valve that control my boom offset instead.

Here is the link to that thread I posted a while back. I still haven't added my bypass valve yet but have been really careful not to overpower the thumb. The first time I tried it I picked up a big cherry tree I had cut down and was swinging it around thinking this is great then not thinking I put a bit too much pressure on the thumb and bent the piston. Luckily I was able to replace it with another from another old cylinder.

http://www.tractorbynet.com/forums/build-yourself/156107-room-another-thumb-here.html

Make sure you do get a bypass valve added if your hoe don't have one. But adding the hydraulics will really be worth the effort when it's done. I didn't have a real plan for mine other than some pictures I found on the internet which I kinda combined all the details I liked and overall it's prob overkill but works like a charm.

Topstrap

 

[ridefst]

Ok, now you guys are just confusing me:confused2:
As soon as I decide to drop the hydraulics, Topstrap posts pics of a very similar setup and likes it :mur:

I've got no problem with the actual hydraulic hookup, the hoe already has an proportional aux control with lines to the end of the boom. Don't know if it's got a bypass in there, I suppose not, as you wouldn't want that for all applications

The issue seems to be the geometry of the whole thing. Topstrap, do you have any pics of your setup with the bucket curled? I imagine that your thumb would overhang the bucket quite a bit, similar to the my early design?
Is that an issue in normal use? How long is your thumb?

 

[dfkrug]

I read on one of the forums about plumbing the thumb cylinder in parallel with the bucket cylinder by putting a tee in the lines for the bucket cylinder and using a manual valve to stop the flow to the thumb when you're not using it. With the valve open, both will move at the same time, but the one encountering the least resistance will move first. If the bucket hits the object first, it will stop and then the thumb will move until it contacts the object and pinches it.

It might be a little tricky to use but you wouldn't need a separate valve and another set of hoses running out to the dipper. It might be more versatile than a fixed thumb.

Mine is teed into the bucket curl circuit, but I use a single spool solenoid
valve to open/close only one side of the thumb cyl. The valve is small
enough to install to the back of the dipper, and the hoses are short. If
a manual valve is used instead, it would take as much or more room and
you would have to get on/off the tractor to enable/disable the thumb.
It would cost about the same, too.

That is the biggest value to a hydraulic, vs fixed thumb.....activating it for
ocassional use, then fully retracting it to return to digging. All from the
operator's seat.

Tricky to use? Not at all. You get used to flicking a switch on the console
to toggle back and forth from fixed to parallel. I have not seen any others
with a parallel-plumbed hyd thumb. Anyone? (I also plumb my 4-in-1
FEL bucket that way, BTW.)

 

[dfkrug]

Don't know if it's got a bypass in there, I suppose not, as you wouldn't want that for all applications

Rather than using a relief valve for the thumb work ports, you should
design your thumb to have the correct diameter cylinder, the correct
stroke, and a long enough moment arm. That way, the thumb and
bucket do not overpower each other and cause breakage.

 

[Topstrap]

Here are a few pictures of it in various postions. Last is with thumb retracted.
The distanced from bucket pin to end of teeth is 35 inches but teeth are worn a bit so prob 36 with new teeth. The thumb is 36 inches long measuring from pivot pin to the end. It does overlap when bucket it curled but from what I've found is that I seldom ever have it curled that far and still using thumb. It's usually open with thumb down to pluck objects rather than curling bucket under as much as in scooping stuff up.

I'm no engineer and have no idea how much figuring and calculating it would take to engineer a thumb for my machine that would handle the leverage that is generated by the bucket when curling it under. It's amazing how much leverage and power it has for just a small machine. I know that because I have a longer cylinder and my thumb does have a long extension travel and the cylinder loses a lot of it's stiffness and strength. Maybe a lot bigger cylinder might be in order someday but I still think the curling power of the bucket would still possibly bend even a much larger cylinder when fully extended. A shorter cylinder might be better but I like having that much travel and have learned to just be careful while grabbing things.

In case anyone is wondering that contraption in the background is my latest project. Old housetrailer frame being modified to make an eventual arched walking bridge to go over the short end of my pond. Prob be about 46ft when done.

Good luck with yours, hope to see pictures of it when you're done.

Topstrap