I built mine. Bought a Bobcat LowPro bucket and added the Grapple. I use two cylinders, with two claws on each cylinder. Lets the Grapple pick up uneven or odd shaped loads better. My claws close on the edge of the bucket between the teeth. I don't see any reason for it to close any tighter which is what you would gain by allowing the claws to go inside the bucket.
Sorry I couldn't find any close up photos of the build but I'll get you some if needed. There's a couple things I want to point out though.
There's no such thing as a light duty Grapple. That is unless you are hydraulicly educated enough to calculate forces exerted at the tips of the claws through the entire range of motion. The ability of the Grapple to grip is going to be determined by the cylinder size, geometric design and hydraulic pressure created by the tractor.
There's no such thing as lightly using a Grapple. By most designs when you activate the circuit the tractor is going to exert maximum hydraulic pressure into the system. The cylinder is going to transfer that pressure and flow into the design of the claw. The claw is going to clamp at whatever force the pressure/flow/design allow.
My point is, don't under build. If you do, you'll destroy your design the first few hours of use. I built mine to what I thought was overkill strength. Had to go back and add more bracing and reinforcement because I started bending the claws.
By design mine has a fairly soft grip when the claws are completely open. The amount of grip increases as they close. By the time the claws are almost closed against the bucket they have tremendous grip. I can pick up a large flat rock with one claw tip and grip it hard enough it doesn't slide out.
I used 2" cylinders with 8" stroke. Your design might dictate something different. But I would suggest determining cylinder size early on in the build. I'd also suggest nothing larger than 2" to prevent overpowering your design.
I guess if you were concerned about the strength of your build you could decrease cylinder diameter size to minimize damage to the structure but I'd avoid that. I'd rather build the design with the strength to handle whatever cylinder you chose to maximize uses.
You cannot imagine what you are going to do with a Grapple. As the useage increases so does the stress on the Grapple. That's when you start seeing failures. My loader and Grapple will pick up loads that my 10,000lb tractor with 1,200lb rear ballast cannot control. Very commonly I have a rear tire in the air. Rather than constantly have to make a seat of the pants determination of whether my Grapple will handle the load I'd rather make that determination of the tractor's ability to handle it. Then I'm not spending all my time in the shop making repairs to the Grapple. I've had my Grapple for almost two years. I'd guess the hours of use at 300. I wouldn't venture a guess at how many tons of material it's handled.
