How to Grapple without a Grapple - Pictures please

[ovrszd]

I like that setup. Have you had any indication that full down pressure on a solid load might bend the top of the rack at the back that the forks attach to?

I was wondering about that as well. But the pics don't give a clear indication of how much force the cylinder can exert.

I built my Grapple on a Bobcat Lo-Pro bucket. I paid particular attention to how I fastened it and braced it to the bucket. I still tore it loose and had to reinforce it even more. With the pressure my cylinders exert I would immediately bend this system backward.

But I like the simplicity of his setup. Hopefully it will hold up and serve him well.

 

[IslandTractor]

Pushing with any significant pressure on the upper grapple arm is a bad idea regardless of grapple design or construction. Upper grapple arms are engineered to pivot and clamp not to stand up to the weight of a tractor or even worse the forces of tractor momentum. Most damage to upper grapple arms and their attachment points occurs with inadvertent (or dumb) pushing the arm against something instead of pushing with the bottom tines which are built for it.

 

[ovrszd]

Pushing with any significant pressure on the upper grapple arm is a bad idea regardless of grapple design or construction. Upper grapple arms are engineered to pivot and clamp not to stand up to the weight of a tractor or even worse the forces of tractor momentum. Most damage to upper grapple arms and their attachment points occurs with inadvertent (or dumb) pushing the arm against something instead of pushing with the bottom tines which are built for it.

I agree.

But what we are talking about is the clamping pressure of the thumb. If the cylinder exerts enough clamping pressure to overcome the bracketry holding the base in place, it will bend the brackets.

The force on the hinge is not just vertical. It's also horizontal. Without adding any pushing force with the tractor.

If you look at your Grapple you will see the hinge points are highly braced and reinforced to control all those forces. In this particular case there is no bracing to prevent the hinge point from moving forward or rearward. Only up and down.

 

[stuckmotor]

I was wondering about that as well. But the pics don't give a clear indication of how much force the cylinder can exert.

I was loading logs on my forks by hand. I tried to muscle one end of a log over the forks and let go too soon. It bent a nice curve into the rop of the rear guard. Mine doesn't appear as heavy as the one in the photo though.

 

[ovrszd]

I was loading logs on my forks by hand. I tried to muscle one end of a log over the forks and let go too soon. It bent a nice curve into the rop of the rear guard. Mine doesn't appear as heavy as the one in the photo though.

Yep. As explained earlier, the forces exerted by a thumb or grapple on the base it's fastened to are tremendous. Some users will say "Oh I'm not going to lift or clamp on anything heavy, just use it for light brush". Whatever. A Grapple setup is one tool that will be used to it's maximum ability repeatedly. The longer you use it, the more difficult and strenuous the tasks become.

 

[IslandTractor]

I agree.

But what we are talking about is the clamping pressure of the thumb. If the cylinder exerts enough clamping pressure to overcome the bracketry holding the base in place, it will bend the brackets.

The force on the hinge is not just vertical. It's also horizontal. Without adding any pushing force with the tractor.

If you look at your Grapple you will see the hinge points are highly braced and reinforced to control all those forces. In this particular case there is no bracing to prevent the hinge point from moving forward or rearward. Only up and down.

Understood. The setup Albionwoods has is atypical but I don't see that hydraulic pressure from closing the grapple arm could do damage to the fork frame. For starters, that fork frame is more solid than any standard bucket top lip where folks routinely mount grapples. Secondly, it seems the forces in closing with the ram would be mostly directly backwards and that is against the strongest dimension of the frame. I might be concerned about pushing sideways against the top of the forks frame but pushing directly backwards looks to me like what it is designed to resist. Of course pushing against a load with more than just hydraulic pressure would potentially damage the mount/frame but that is true with any grapple. A third point is that forks grapples are typically not used to grub in brush or to uproot trees but rather to carry brush and logs. The typical use of a forks grapple would therefore seem to provide few risks to the upper grapple arm mount.

 

[IslandTractor]

Yep. As explained earlier, the forces exerted by a thumb or grapple on the base it's fastened to are tremendous. Some users will say "Oh I'm not going to lift or clamp on anything heavy, just use it for light brush". Whatever. A Grapple setup is one tool that will be used to it's maximum ability repeatedly. The longer you use it, the more difficult and strenuous the tasks become.

If you mean that maximum hydraulic pressure on the ram is typical I would agree but that is precisely the force that every grapple is engineered to resist. Doesn't matter what the load is, clamping pressure is always the same. It's the dynamic forces of ramming or leveraged forces pushing on the open upper arm that are dangerous. I've never heard of any grapple bending while just clamping with max force on a load.

 

[ovrszd]

Understood. The setup Albionwoods has is atypical but I don't see that hydraulic pressure from closing the grapple arm could do damage to the fork frame. For starters, that fork frame is more solid than any standard bucket top lip where folks routinely mount grapples. Secondly, it seems the forces in closing with the ram would be mostly directly backwards and that is against the strongest dimension of the frame. I might be concerned about pushing sideways against the top of the forks frame but pushing directly backwards looks to me like what it is designed to resist. Of course pushing against a load with more than just hydraulic pressure would potentially damage the mount/frame but that is true with any grapple. A third point is that forks grapples are typically not used to grub in brush or to uproot trees but rather to carry brush and logs. The typical use of a forks grapple would therefore seem to provide few risks to the upper grapple arm mount.

Where his setup has exceeded the manufacturers assumed stresses is that he added what appears to be 12" of vertical height to the fork frame. So now he has created a lever. The forces of the thumb are hugely magnified at the fork frame base. It was never intended to be exposed to that. Add the fact that their is no way to brace his addition to stop it from moving forward or backward and you have the distinct possibility of failure. If it fails, I expect it to bend his bracketry that he's added to the fork frame before it actually curves the frame. But when failure starts, it expands. And it will probably be noticed too late. "What's going on, my thumb isn't closing all the way????" Too late.

But I hope it works. He has certainly expanded the ability of his forks. Which again places forces on them they were not designed for. It would be interesting to send the Fork Manufacturer a picture of this setup and ask them if this voids their warranty??

 

[ovrszd]

If you mean that maximum hydraulic pressure on the ram is typical I would agree but that is precisely the force that every grapple is engineered to resist. Doesn't matter what the load is, clamping pressure is always the same. It's the dynamic forces of ramming or leveraged forces pushing on the open upper arm that are dangerous. I've never heard of any grapple bending while just clamping with max force on a load.

Remember, we are not talking about a manufactured Grapple. We are talking about a light duty fork set that has been modified.

As for load pressures. It certainly matters what the load is. The clamping pressure will exert it's forces back into the hinge point differently almost every time something is gripped. Even with repeated loads of loose brush the forces will move.

I agree about not abusing the open claw. Another no-no is rolling the Grapple forward and clamping onto an immoveable force and then moving the tractor rearward. This can pull the hinge point forward with forces beyond it's designed capability. It can also exert compression forces on the cylinder that it can't withstand bending the ram, blowing hoses/seals, etc.

A Grapple needs to be used with consideration and attention to detail concerning the goal.

 

[IslandTractor]

Where his setup has exceeded the manufacturers assumed stresses is that he added what appears to be 12" of vertical height to the fork frame. So now he has created a lever. The forces of the thumb are hugely magnified at the fork frame base. It was never intended to be exposed to that. Add the fact that their is no way to brace his addition to stop it from moving forward or backward and you have the distinct possibility of failure. If it fails, I expect it to bend his bracketry that he's added to the fork frame before it actually curves the frame. But when failure starts, it expands. And it will probably be noticed too late. "What's going on, my thumb isn't closing all the way????" Too late.

But I hope it works. He has certainly expanded the ability of his forks. Which again places forces on them they were not designed for. It would be interesting to send the Fork Manufacturer a picture of this setup and ask them if this voids their warranty??

I assumed that extension was part of the fork frame and engineered by the manufacturer to prevent loads from falling back onto the tractor. If he added it himself it is certainly a professional looking and pretty well engineered extension. Assuming the manufacturer designed the "bridge", I'd also assume it is engineered to withstand a ton or more of pressure. It actually looks like an oversized grating so should withstand backwards forces pretty well.