Thumb thumb in action and more.

[gray]

I am trying my first picture post. It sould show the thumb I just put on my BH. It also may show the big lake ( Superior ) in the back ground.

I have been practicing with it and finding out how to best use it. I have also found a weekness in this thumb design. Nothing that will stop it's use just a design weekness.

I hope this picture works out.

 

[cherokee1]

Wow, that is some load to cantilever. I just bought a 10000# excavator am anxious to see just how much it will pick up in comparison.

 

[gray]

My guess is that the 10000lb would have about a 2000lb +or - 500 boom lift based on the distance out from the base pivot you are lifting from? My machine has between 1000 and 1400lb lift. My guess is that it lifts more than the specs rate it for. the machine wieghs in at 7800lbs but it is not designed for digging alone. Yours should easily do much more than you see in the picture- much more.

Is it equiped with a thumb?

 

[Gary_in_Indiana]

Is your thumb fixed or adjustable? If it's adjustable, is it manual or hydraulic? Thanks. /forums/images/graemlins/smile.gif

 

[gray]

It's manual and adjustable. 3 positions plus folded up- out of the way. It is from Excavator Thumbs.com. It is heavy built and accurate but has one flaw that I know of and will keep in mind when in use as to not do damage to it or the hoe.

 

[v8dave]

What is the flaw? Or are you going to keep us guessing?

 

[gray]

Dave,

The flaw as I see it is that the main pin is run through a single 3/4 inch plate that is welded to the dipper stick back plate. It is strong but did bend a bit with a heavy offset grapple of the tree in the picture. I discovered this after taking the picture. I am guessing it is about 3degrees bent. The thumb still functions properly but I beleive if it had a wider pin base and base plate it would resist this type of twist much better.

It does have a 2 inch main pin that is more than enough. I am not a mechanical engineer but I do have some experiences with design and stresses. It will provide good service as long as I remember not to put too much twisting stress on it.

I was just not too sure it is much of a flaw but after thinking about it for a while- it is something to mention.

 

[gray]

Dave,

More info on the thumb. I took a close up picture so you could see the plate I tweeked.

I used it tonight for a few hours and here are my findings:

Scale of 0-10

Function when set up- 9

Ease of set up adjustments-2

fold out of way option-2

overall design-6

Major needs. tool free adjustments
2 plate base pin mounting to resist twisting
Tube in tube stiff arm
Quick fold away system

Yes, it work good when set up- I just like things designed to set up and take down better. I will get/ plan to get lots of use out of the thumb.

 

[v8dave]

I hadn't thought of the twisting aspect of a thumb. But, it makes sense. I did think about the rotation center of the movable thumb and bucket I rented. So, I took some pictures in case I ever got the idea of adding one to my backhoe.

Here is the first of two I'll post here. Notice the thumb uses the backhoe pin/pivot as it's pin also.

 

[v8dave]

This picture shows the wide attachment pin better. A nice wide attachment like this would help transfer the radial load better. Although, a radial load with this beefy attachment might transfer the bending moments to a more expensive place to repair. Sometimes, a weak point is a good thing--you never know.

Thanks for the heads up. I'll keep this in mind if I ever get a thumb. On the other hand, maybe I'll just keep on renting the Bobcat excavator for the rare occasion I need one.