I am building a single Grapple on a spare bucket. Because of having alot going on and i think i will like 1 grapple over 2 i will build it this way. It will be a thousand times better than no grapple. I am using field cultivator shanks. I dont know about welding on them so i may use ubolts to join them .
I had planned to cut the shank off but i may try to drill a new hole to pin it in the tubing hinge,
I am close to being done the cylinder mounts have been a problem because i think the more stroke i use the better leaverage or clamping force i will have . Has any one here built there own grapple if so are you happy with it?
I had a homemade grapple that my dad had made me from an old bucket I gave him to use. Worked great, and used it for years. The guy was a master fabricator. He could think it, and make it. He operated under the belief that when in doubt add more steel. The bucket is back at home now (ND), but next time I get a chance I will take a pic of it and post it. As to more stroke adding more clamping force, I am not a hydraulics engineer, but I think to add more force you need to increase cylinder size and/psi to achieve that. Positioning of the cylinders can make it more efficient, but I don't believe that more stroke alone achieves that.
I think what Doug meant is moving the cylinder pins further from the pivot will put more force on the grapple, but less movement for the same size cylinder. For instance, if you had a typical 8x3 cylinder mounted ten feet from the pivot, it would break the grapple before it stalled the cylinder, but it wouldn't move the grapple enough to do anything. OR, You could put the cylinder pin 3" from the pivot, and it would operate fast, and the whole range of the grapple, and easily stall the cylinder to avoid bending anything. IF it was me, I'd have to temporarily weld a mock up of the mounting, or use hose clamps or wire to mount the cylinder then operate it by hand to get a feel for how the range will work with the stroke of the cylinder. I've heard of using cardboard or plywood also, that would be with a piece of cardboard or a stick cut for the length of the cylinder closed and open.
Thats what is bothering me if i dont use alot of the stroke it will mean that it opens fast and dosent have much force. I will weld up every thing but the back cylinder mount and see how it works. The first ideal i had it would open and close in less than 3 inches of stroke.
Sorry, I miss understood the issue.
I wanted to make a grapple, but my lack of available time drove me to buying one instead. I picked up a single clamp, dual cylinder model, similar to what you are building. The hydraulic cylinders are 3" diameter x 12" stroke. The grapple is designed to use the entire stroke. As mentioned by @KSSS , cylinder diameter and system operating pressure determine your max force that can be provided by the cylinder. This force can be amplified by extending their mounting point farther behind the pivot point, ie: a lever. First step is don't use too long of a stroke, or else you won't be able to capitalize on the lever concept to increase your applied force to the grapple tines. Also, the lever arm length affects the rate at which the grapple opens and closes, coupled with your skid steers hydraulic output. I will take some pictures and measurements off my grapple in the daylight and share. That can help give you an idea of what to do with yours. My closing/opening rate is fine, and can be adjusted with throttle position if I need slower. Clamp force is excellent as I have latched onto logs that I couldn't pick up, but the grapple wouldn't drop either.
Last night i tack welded the back mount were i had the 2 parts clamped then i opened the grapple up with a engine hoist it opened about 24". It wedge the 2 parts 2" apart now its using bout 10" of its stroke. I will work on it agin today. Then my next deal is my case dosent have any extra hyd outlets to run it. I have a parts rig that i will take as much off of to rig it up. Then i need to see if i can get tapped into the hyd on it buy a valve to switch from bucket tilt to grapple. This machine could have extra hyd but it was rare there is a plug on the side of its valve that is removed to do this but i cant get my head wrapped around how this works.
I finely got my skid steer rigged up with a extra set of hydraulic outlets. I ran some hoses to the bucket so i could opened and close it. Now i need to finish welding it up.
I lay it out on CAD. I draw cylinders as circles. The smaller circle is the retracted pin-to-pin length (the radius) and the larger circle is the extended length. That will intersect where your grapple swings at both extremes of the grapple's swing.
I dont think it opens as far as most do but i am going to weld the cylinder mounts up and try it. The mount on the grapple is bolted so it could be moved. I didnt know any thing about the cylinder i am using so i took it apart and rebuilt it $25.00 for parts. I need to make a clamp for the hose couplers and build a linkage to make my selector valve foot operated. I cant wait to put it to use . I have a dead tree to cut up and load first thing.