Homemade grapple help
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    Leney's Avatar
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    Homemade grapple help

    Hey
    I'm in the process of designing a grapple, i am trying to figure out what length of stroke I will need for my cylinder.
    I have never built anything with a hydraulic cylinder before so not too sure exactly how it will work.

    I am drawing the grapple in autocad, and based on my design I need a 3" stroke cylinder, which seems really short and not sure how I get so much movement out of the top jaw

    I expected to need at least a 6"

    Anyone with grapples, how much stroke do you have for full open to full closed?

    does my drawing look like it should work just fine with the 3"?

    thanks in advance for any help!

    Click image for larger version. 

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    Keeper of the GTT Cookies dieselshadow's Avatar
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    You're not giving that cylinder much leverage. Try moving the stationary cylinder mount up a few inches.
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    Couple of observations:

    1. As Dieselshadow said. I would raise the fixed location away from the arm for more leverage.

    2. I would also move the grapple attachment point to utilize the max range. No sense in using a 24" cylinder if you only need 3".

    3. With a design with only 3" of travel, the flow is going to need to be valved way back. That grapple is going to FLY open or closed. You can also over size the cylinder bore, but that gets expensive.
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    3x8x1 75 Double Acting Hydraulic Cylinder 9 5460 A | eBay

    Looks like they are out of stock. 2 cylinders w/shipping was 123.00

    I used 1" 4140 round stock for my pins, bought from a local machine shop. Used 2 plumb bobs and a magnetic torpedo level to insure the pin axis remained level and parallel to the axis of the square tubing frame. I left the 4140 long for this purpose and simply measured from the plumb strings to the frame and then to the pin to insure the distances were equal on both ends of the round stock.Click image for larger version. 

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    I tried to pick out pics that would best show the relationship between the grapple pivot point and the center of the cylinder pivot pins.

    ETA: Bear in mind that my grapple is for a 55HP tractor but built to withstand probably one twice that size. It is 80" wide. I do not know what size tractor you have and you need to design accordingly.
    Last edited by mtrmn; 03-06-2016 at 07:52 AM.
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    thanks for the suggestions fellas!

    I have moved the stationary mount up a couple of inches, and also moved the mobile one a bit, I now have a 6" stroke and the geometry looks a lot better.

    as far as cylinder bore.....I was planning on using a 2" because they are on sale right now, but I see some of the grapples online that actually list their cylinders are using 3-4"

    the 2" I am looking at has 10,000lbs of force, why would I need more than that?
    or are the larger bores being used just to slow it down as fred suggested?

    thanks again for the help


    Click image for larger version. 

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    johnH123 likes this.
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    figure the down force

    Quote Originally Posted by Leney View Post
    thanks for the suggestions fellas!

    I have moved the stationary mount up a couple of inches, and also moved the mobile one a bit, I now have a 6" stroke and the geometry looks a lot better.

    as far as cylinder bore.....I was planning on using a 2" because they are on sale right now, but I see some of the grapples online that actually list their cylinders are using 3-4"

    the 2" I am looking at has 10,000lbs of force, why would I need more than that?
    or are the larger bores being used just to slow it down as fred suggested?

    thanks again for the help


    Click image for larger version. 

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    I would figure the actual down force on the grapple, particularly the points or teeth. With a low angle, it might surprise you what the actual force at the tooth end is, particularly when almost closed. (Hmmm, is that the sine of 10 degrees or so. Dang, trig was a long time ago.)

    At some point in my future, I will relocate the cylinder on my manufactured grapple as others have suggested. I'll move it higher and probably replace the cylinder with a longer stroke as mine doesn't quite close all the way. It's very workable the way it is, but could be improved. A higher mounting point and longer stroke will help both the closing force and the tooth to frame gap on mine. The downside might be that the grapple won't open quite as wide as it currently does. That's the other dimension you will want to look at, does the top arm open enough for your projected use.

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    Jim Timber's Avatar
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    I got a couple 3.5x8x1.5 or 1.75 (I forget which) from Surplus Center for $50 each plus postage that I was going to use for my grapple before buying a Woods out of expediency. The 2.5" on many commercial units are under sized to increase speed and they're still not all that quick with a 11gpm pump pushing them. The clamping force is marginal in my opinion. These having such a large range of motion reduces the effective gripping substantially. This isn't to say they're going to lose a grip on something reasonable, but the leveraged forces involved in clamping a large log are greater than the force capable on the lever with the cylinder bore provided. These jaws take a remarkable amount of pressure when you factor in all the geometry and physics involved in use. Everything's a compromise because weight becomes a limiting factor against strength - you cannot over build this tool, you can only make it too heavy to use with your machine; thus some medium must be accepted.

    If we had more flow, it'd be cool to make a twin hinged lid. You could have a lot opening with a second hinge - think of your fingers, they have 3 joints.
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    Quote Originally Posted by Leney View Post
    thanks for the suggestions fellas!

    I have moved the stationary mount up a couple of inches, and also moved the mobile one a bit, I now have a 6" stroke and the geometry looks a lot better.

    as far as cylinder bore.....I was planning on using a 2" because they are on sale right now, but I see some of the grapples online that actually list their cylinders are using 3-4"

    the 2" I am looking at has 10,000lbs of force, why would I need more than that?
    or are the larger bores being used just to slow it down as fred suggested?

    thanks again for the help


    Click image for larger version. 

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    leney,

    hope you dont mind, but i had time to kill so i looked at your drawings and put it into 3D. i dont have the clamp(s) done yet, but here is the rake:

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    i tried to follow it as close a possible, but there are a few small variations. hope you like it!
    mjncad, JKR, OldmanX and 4 others like this.
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    Leney's Avatar
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    hey that's really cool, thanks john

    my design will have 7 lower jaws and 4 uppers


    anyone else have any input on cylinder size?
    johnH123 likes this.
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    if you have something that can open .SLDPRT and .SLDASM files i can send them to you if to want.
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