DIY thumb for tractor bucket

[davedj1]

Nice , looking to make one for my b7100

Thank you. I am really glad I had it today, decided to get the rest of the wood home ASAP so I just cut it all to 118" and loaded it in the dump trailer.
Two loads and I was done, then I brought the tractor home I am sure I will use it for some spring cleaning of some old metal truck parts we dug up a couple of years ago while installing new septic lines...lol

 

[davedj1]

So now that my tractor is home I took the thumb off and straightened the bucket top out, picked up a piece of 4" x 4" x 3/8" angle iron and went to town.
I had to cut the two hooks I had put on the top of the bucket but I'll reattach them to the angle iron tomorrow. I can't get Imgur to cooperate so I can't get the pictures off my phone to post here but I'm working on an alternative route. Anyway it seems much stronger and less flex than before. I have not attached the back brace to the back of the bucket, not sure If I need to yet or not.

 

[davedj1]

Here are the pictures, finally got them to upload to Imgur

I'm thinking about adding a brace from the channel to the bucket in the front? Thoughts on that , just a 4-6" piece or so?

 

[ovrszd]

The amount of stress applied to the bucket is always underestimated. I used 4"x1/4" square tubing. Tore it loose from the bucket and had to add more bracing.

If I understand correctly, you are considering adding a brace from the "front" edge of the channel downward inside the bucket and welding to the bucket vertical back?? I didn't say that very well.....

If so, yes that will help considerably. Maybe add two, one under each hinge pedestal??

The idea is to keep the assembly from rolling backward.

Trust me on this one,,,, it's much easier to over build now while everything is relatively straight rather that tear it loose from the bucket and then try to repair.....

 

[davedj1]

The amount of stress applied to the bucket is always underestimated. I used 4"x1/4" square tubing. Tore it loose from the bucket and had to add more bracing.

If I understand correctly, you are considering adding a brace from the "front" edge of the channel downward inside the bucket and welding to the bucket vertical back?? I didn't say that very well.....

If so, yes that will help considerably. Maybe add two, one under each hinge pedestal??

The idea is to keep the assembly from rolling backward.

Trust me on this one,,,, it's much easier to over build now while everything is relatively straight rather that tear it loose from the bucket and then try to repair.....

Yes, you understand correctly. I have a piece of 6" wide by 3/8" that extends down the back of the bucket and was bolted through with another piece on the inside to help back it up, I have not bolted it back up yet. Maybe I'll incorporate the front braces to tie into the rear one?
You are right about forces, hydraulics are no joke. My bucket was actually pushed up and back from using the thumb, I chained the thumb down and managed to get the bucket pretty much back to it's original shape then some clamping and hammering with a bfh to get the angle lined up. There will be no work done on it today as I woke up at midnight feeling as though I had ingested a box of razorblades and they are stuck in my throat! I hate being sick!

 

[ovrszd]

Sorry to hear of your illness Dave. I'm extremely Blessed in that regard. Haven't had a cold in the last 7 years. Can't remember the last time I had the flu, guessing over 20 years.

Yes, I'd add the front braces. Better overkill than failure.

A bfh is my "go to" tool.

 

[davedj1]

Thank you sinesterbiker.
Here are the last two loads I brought home in 118" lengths (dump trailer is 120")

I'm going to add two more teeth to the bucket, one on each side of the grapple, The two on the ends of the bucket work well for longer lengths but I'm thinking two more for shorter stuff (big rounds). The ones on there stick out 8" , I'm glad I didn't make them any shorter.

 

[Dave M7040]

I admire your ingenuity and fabrications skills.

Plse let me point out one hydraulic aspect so you can at least consider it.

Many backhoes have thumbs to act like your grapple.

The thumbs are usually fixed and not hydraulically powered.

There is a good reason for that.

At this point, to better explain myself I need to wander a bit.

If you connect a pressure gauge tee'd into the push line for your grapple, you will read the pressure of the relief valve setting on your tractor. Lets say 2,000 psi to keep things simple.

I again will use a simple number (4 square inches) for the number of square inches on the piston in your grapple hydraulic cylinder. Therefore your push force will be the system pressure of 2,000 psi x the piston area of 4 sq inches which equals 8,000 pounds of push force.

If you disconnect the retract hose from its quick coupling, you now have fluid trapped on one side of your cylinder's piston.
The area of the piston, when you subtract the area of the push rod shaft, will be less than 4 sq inches, more like 2 square inches.

Now this 2 square inches is having to use a much higher hydraulic pressure to keep the piston stationary. You have 8,000 pounds of push..
The piston is not going to move because fluid does not compress.
You have 2 square inches of area

So you have 8,000 pounds of push being resisted by 2 square inches on the retract side of the cylinder's piston. 8,000 divided by 2 square niches means the pressure on the retract side of the cylinder will be 4,000 psi. The tractor's hydraulic pressure has been amplified 2 x

When you use a control valve to extend or retract a cylinder, the relief valve only provides protection when the cylinder is moving and the control lever is not in a neutral position.
Once you release the valve lever the fluid is trapped and can rise to very high, even damaging levels..

Consider the backhoe bucket thumb. You add a hydraulic cylinder to allow you to easily adjust the position of the thumb. As the thumb closes, the bucket is stationary. The fluid in the bucket cylinder has no where to go. As the thumb squeezes against the bucket you can have serious hydraulic amplification taking place. The relief valve cannot protect the fluid in the circuit being amplified.

I am not an expert in either grapples or thumbs so my words are cautionary. Perhaps putting a few hydraulic gauges into the circuits on a temporary basis will let you know if you can be at risk of damage.

This photo is of a hydraulic double acting cylinder for a front mounted plow on a small tractor.
Look closely and notice the snap ring hanging off the push rod and the cylinder end partially out.

The owner was trying to center the plow blade. When it would not move right, he increased to full rpm's and tried again. At that moment the end of the cylinder was forced out.

This next picture is of the damaged groove for the snap ring. The line for the retract side of the cylinder was not properly seated in the quick coupling leaving fluid trapped in the retract end of the cylinder. When the pressure was amplified, the snap ring destroyed its groove and the cylinder end came out.

This is an area where cross over relief valves might have a use. They are usually found on pickup truck plows to relieve pressure if the blade hits something solid.

Dave M7040

 

[davedj1]

Dave, I'm not sure I am comprehending all that at the moment as I just came to from a nap and I'm under the weather but I will review it in a day or so when the old soft computer hard drive is a little fresher. Thank you. I do understand the crossover relief valves in pickup plows, I've rebuilt several Meyer brand pumps.

 

[davedj1]

Dave, something I just thought about as I was re reading what you wrote the other day. In your example of a backhoe bucket and thumb one exerts force on the other. In my thumb application this does not happen as the thumb moves with the bucket tilt and not against it. I'm guessing the only way I would have increased pressure on the cylinder would be if a large log was drooping thereby pushing against the thumb?