QUESTION: sizing a hydraulic cylinder for a DIY grapple bucket

TSO · Sep 15, 2013

Howdy... I'm building a single lid grapple bucket. 60" wide bottom, 32" wide top. Tractor is 47hp, weighs 5000 lbs, lifts 2650 (for power/sizing info related to strength issues).

What size (bore & psi ratings) cylinder do I need to have the strength I need, while still being affordable & durable? I'm only planning to use 1 cylinder with the lid. Also, what is the best way to determine (sight unseen) what overall length I need to place the pin locations for the cylinder ends, in relation to the stroke length? For example, if the cylinder is advertised as an 8" stroke, is there a common length I should use to determine the actual measured points that the "knuckles" will need to be spaced at (I'm assuming it's at least 3 additional inches overall from quick peeks) so I know what the shortest overall measured length will be while the grapple arm is retracted and in the "up" position?

And, is there a way to operate the cylinder by hand, WITHOUT having it hooked up to the lines, so I can be sure the stroke length works with my pin placements & such, before I finish weld everything?

Also, my local farm store (called Family Farm & Home) has this cylinder (Delavan Pumps Inc)... the price seems ok at around $80. It's 2.5 bore X 8" stroke. I don't think it's retracted all the way. How's the brand? Good, bad, ugly, other ???

Thanks in advance.

Zebrafive · Sep 16, 2013

Normally an 8" stroke cylinder will be 20 1/4" pin to pin centers retracted. There are shorter versions that will measure 18 1/4" retracted.
I think the cylinder you pictured is fully retracted.
Remove both plugs from the ports to move by hand.
The psi of the cylinder should be sized to the tractor's output.
One other thing to consider is rod diameter, I'll guess it 1 1/8" You can also find 2 1/2 bore cylinders with 1 1/4" rods.

J_J · Sep 17, 2013

Never heard of it, but that does not mean that it will not work well.

You need as much cyl as it takes to open the grapple all the way and provide a good gripping force.

Arc weld · Sep 17, 2013

That looks like an implement cylinder and they do have a standardized SAE extended and retracted length. To figure out the pivot points and other info you need, you have to look at some grapples and do some designing and measuring on your own. That cylinder is a basic low end farm cylinder but should work OK for what you need. I just had the stick cylinder fixed on my Cat backhoe. The retaining bolt for the piston stripped out of the cylinder rod. It was a 4" bore x 34" stroke cylinder. Total repair cost was $1275.00 and they reused the cylinder rod. A new cylinder rod would have been about $400 more. They said a complete new cylinder from Cat would probably cost 4 or $5000.

:shocked:

J_J · Sep 17, 2013

Make a wood stick that represent your grapple.

If you have no cyl to go by, then use some PVC so one piece slides inside the other.

Place one end where the base end should go.

Slide the other piece to where you want the rod end to connect.

That should give you the stroke and length of the cyl you need.

Cyl size could be 2 to 3 in bore.

2 in cyl, 1 in rod, 2500 psi = 7854 lbs

3 in cyl, 1.5 in rod, 2500 psi = 17,671 lbs

If you use 2 cyl, you will have twice the force.

ovrszd · Sep 17, 2013

Good answers so far. I built my Grapple with two Claws using two 2x8 cylinders. I struggled trying to properly locate the brackets for the cylinder ends. I'm not a mathematical genius so couldn't just draw a plan and make it work. A lot of trial and error. In the end I get great claw range of motion. The only thing I lack is cylinder gripping force when wide open. Once the cylinders start closing the Claws the force increases as they go. By the time they are closed the Claws have tremendous gripping force. With dead wood of small branches they crush them if not careful. For an example, I can pick up a 55 gallon metal barrel with one open end and crush it in the Claw's grip. Here's a few pics to maybe help in your design. Again, sorry I can't give you technical answers in how to locate your cylinder brackets. A LOT of mathmatics come into play.

I'm sorry about these crappy pics. I'll scrounge and find some that show more fine detail about how my cylinders are mounted. As I said, it was a ***** to figure out. With arched Claws the first problem I had was my cylinder barrel falling thru the arch path of the claws as they closed. Put the cylinder in danger of being bent. I added a skid plate under each barrel to protect them from any protruding material that is being gripped.

The force numbers that JJ posted give you an idea of each different cylinder sizes ability to exert straight push force. All that changes when you add the geometric angles of your hinge points and cylinder mounting points. This mathematical mystery is why my cylinders exert minimal force when the claws are fully open and that force increases as they shut. Not intentional, just worked out that way. I'm anxious to see your design and build.

Oh, one last point, my claws will clamp tight against the lip of the bucket. The cylinders are within 1/4" of being fulled extended when that happens. I wanted that so I could grip something small. Secondly, when my claws are fully open and the bucket is rolled completely back the claws lack about 2" of hitting my bucket cylinders. Those two things you have to design into your build. Miss either one of them and you'll be cutting everything back apart!!!

stub · Sep 17, 2013

I did what JJ suggested when I build mine. 1/2 inside of 3/4 PVC pipe sliding with T's at each end to figure out the stroke.
I ended up using a 2x10x20 1/4: Surplus Center - 2X10X1.125 DA HYD CYL W200100
I think 8" would have worked but I wanted to make sure I could get it all the way open.

TSO · Sep 17, 2013

Well fellas last night I ordered a cylinder, it's 2.5" bore, 8" stroke, non ASAE, 2500psi, straight column load rating around 12500lbs. Should do the trick, now it just needs to get here. Luckily I have all the dimensions needed for the pin spacing so I should b able to fab up everything before it gets here.

QUESTION: is 3/8" hydraulic line Ok? They have 4000psi line in long lengths at my local store.

Zebrafive · Sep 18, 2013

3/8 is fine. Some even use 1/4 to slow it down. My 2030 only puts out about 8 to 9 gpm so I used 3/8 hose on my grapple also connected to a rear SCV.

Xfaxman · Sep 18, 2013

TSO said:
Well fellas last night I ordered a cylinder, it's 2.5" bore, 8" stroke, non ASAE, 2500psi, straight column load rating around 12500lbs. Should do the trick, now it just needs to get here. Luckily I have all the dimensions needed for the pin spacing so I should b able to fab up everything before it gets here.

QUESTION: is 3/8" hydraulic line Ok? They have 4000psi line in long lengths at my local store.

If the grapple moves too fast, check this thread: http://www.tractorbynet.com/forums/...-aux-hydraulics-jerky-grapple-attachment.html