Custom hydraulic backhoe thumb

[Kernopelli]

I went and bought some 3/8 .063 tubing at Home Depot and re-did
it. My next post will show the finished custom cylinder.

I am curious about the tubing you got at H.D. When I made my FEL I had a hard time finding hard lines and ended up using hose for everything, I would still like to replace them. Can you tell me more about the tubing you used? Obviously it will withstand high hydraulic pressure...I'm surprised they carry something like that.
Thanks

 

[dfkrug]

I am curious about the tubing you got at H.D. When I made my FEL I had a hard time finding hard lines and ended up using hose for everything, I would still like to replace them. Can you tell me more about the tubing you used? Obviously it will withstand high hydraulic pressure...I'm surprised they carry something like that.
Thanks

HD has a rack of raw weldable steel. One thing they have always carried
is some 3/8" ID tubing. It has about 1/16" walls and I think it was in
3-ft sticks. Works great, but use good mandrels if you want to bend it
much.

 

[RedDirt]

Thx, MJN & RED

The hyd fluid takes the path of least resistance and pressure is always the same in each cylinder.So what you see in operation is usually either the bkt or thumb moving byitself until it touches something, then the other element moves.

Excuse me for missing the price quote earlier. Your expanded dialog was helpful though.

Have you used the hydraulic thumb enough to to see whether the preferred operation method is locking the thumb in position and moving the bucket toward it or having both the thumb and bucket move together.

You say "either the bucket OR the thumb moves by itself...". Why is this an "either" situation? Is it just the dead weight of either at a particular boom angle that makes one movement override the other? Is the override predictable? IE can you tell which one is going to move first, as in choosing where to position the boom when setting up to grab something?

 

[RedDirt]

I can get these chrome-plated 25mm pins
pins for very reasonable prices from the Prairie Dog backhoe manufacturer.
I will use cir-clips to retain them. These seem to work a bit better than
bolts, hair pins, or retention clips.

I googled Prairie Dog Digger & Prairie Dog Backhoe and could not come up with a manufacturer. Do they have a web site? I like the cir-clips pins for some applications and would like to check out what they've got.

Thanks

 

[dfkrug]

Have you used the hydraulic thumb enough to to see whether the preferred operation method is locking the thumb in position and moving the bucket toward it or having both the thumb and bucket move together.

Having both cyls operate at the same time is vastly better than just
having a fixed thumb. When fixed at one position, I almost always have it
at full retract to get it out of the way for serious dirt digging. My mock-up
with my 2x8 cyl provided all the functionality I current have, except for the
full retraction and I put a bunch or hours on it. (I was waiting for the
right cylinder to come along.)

You say "either the bucket OR the thumb moves by itself...". Why is this an "either" situation? Is it just the dead weight of either at a particular boom angle that makes one movement override the other? Is the override predictable? IE can you tell which one is going to move first, as in choosing where to position the boom when setting up to grab something?

Imagine 2 scenarios: the first is where the dipper is extended outward
and both the thumb and bkt are fully retracted. If I operate the curl circuit,
only the bkt moves initially because gravity helps out and the bkt provides
less back pressure on the bkt curl cylinder. As the bkt nears about 3/4 of
its curl travel, the thumb starts to move since now the backpressures favor
the thumb cylinder. In the 2nd scenario, I have the bkt and thumb fully
retracted and a big rock positioned to grasp. As I operate the curl circuit,
the bkt moves toward the rock, then stops as it touches it. Then the
thumb moves toward the rock. It is quite predictable and the rock does not
get moved before it is grasped. If you go back and look at the articulated
thumb I made, where the thumb and bkt actions were linked, I often got
into situations where the thumb action would lift the hoe before I contacted
the object I was trying to grasp. Or the bkt would move the rock before
the thumb could grab it. On an excavator I operated a few years ago,
I would position the bkt on the back side of the rock, then extend the
thumb with the foot pedal. With my current setup, those actions are
automatic. I do not feel I have many ANY compromises by not using a
separate spool valve or full diverter setup.

 

[dfkrug]

I googled Prairie Dog Digger & Prairie Dog Backhoe and could not come up with a manufacturer. Do they have a web site? I like the cir-clips pins for some applications and would like to check out what they've got.

RED:
The parts are not listed on their website. I use parts diagrams and order
the specific part by number. The best bet is to order by telephone at

Grand Blanc Tractor sales in Saginaw, MI.
810-694-5314

You can PM me for some part #s if you know what you want. I am not
sure you want to tell them these are not for one of their hoes. The longer
of these pins are about $15 ea. plus shipping.

 

[RedDirt]

dfkrug,
Thank you for the fine explanations. It makes perfect sense and it works as I imagined it would. That's a fine set up you've got now. I had in mind to just build a fixed thumb next winter but now you've got me re-thinking hydraulic.

As far as needing pins from Prairie Dog I don't have a build project going right now. I work the tractor in the summer and work on it in the winter. I had hoped there was an online catalog available so I could pick and choose appropriate pins when the need arose. Thanks for the PM offer but I'll use other sources unless I find I absolutely require a cir-clip style and can't find them elsewhere.

 

[tlbuser]

I do not feel I have many ANY compromises by not using a
separate spool valve or full diverter setup.

Interesting concept you hit on. So, just using the path of least resistance until they equalize? How did you plumb it in so that the thumb has "pressure" all the time for it's static positions?

I've had good luck getting parts at Progressive Power and Control , kinda far from you, but UPS goes almost everywhere

 

[dfkrug]

RED:
The biggest value in finding pre-made 25mm pins is how well they fit
inside 1.000" DOM tubing. 25mm or 63/64 rod is hard to find at your
local steel dealer. It is also nice not to have to drill for the recessed
zerks in the end.

 

[dfkrug]

Interesting concept you hit on. So, just using the path of least resistance until they equalize? How did you plumb it in so that the thumb has "pressure" all the time for it's static positions?

I've had good luck getting parts at Progressive Power and Control , kinda far from you, but UPS goes almost everywhere

My solenoid spool valve, when de-energized, simply blocks the flow of
oil to one side of the thumb cylinder. This converts the thumb to a
fixed thumb since oil can no longer enter or exit EITHER side of the cyl.
There is no need for a 2nd valve at the other cylinder port.

I checked the website you referred to, and I do see they carry several
brands I use. I will try them next time I need a quotation.