Grapple Design

[3RRL]

dtd,
IMO, 1/4" is to skinny. I would use 3/8". Why??
With the added jaws there is a better chance of only one of them hitting and oddball shaped object which places more strain and stress on the whole jaw assembly. It will tweak easier being wider since the force is in the center and the farthest jaw from center seeing resistance will tweak easiest. I would also add more reinforcing between each jaw to tie them together for the same reason. Especially since you are using only one cylinder in the center. I think that is why you see the full width grapples having 2 cylinders. But I like the idea of the wide grapple to suit your needs better.

Please don't be offended, again IMO (my 2¢ worth)...
I don't see having the two end jaws in line with the bucket cylinders as adding strength to the grapple itself, other than that is where you bucket is attached to the fel arms. So the bucket is stronger (backed up by fel arm connection), which in turn makes for a more stable grapple base.

But the grapple strength relies on the manner it is constructed. That is, how well each jaw is connected to each other and the single cylinder mount, the pivots on the bucket, resistance to twisting and tweaking, etc.
I guess what I'm trying to say is although they are all intertwined, failure of the grapple (strength issues such as bending, tweaking etc) is not related to the loader arms.

As an example, I made a thumb for my backhoe. The thumb looks and works like a miniature grapple jaw and was made of 3/8" thick material. The power force points were almost directly in line with each jaw. So I thought with my clever design like that, it would work great and not tweak. It was only 12" wide too.



Even designed like that, since I did not have enough bracing in between the two jaws, I still tweaked it and had to reinforce it more. I grabbed an oddball shaped log and one jaw wanted to go farther down than the other...and it did. Just sharing from real experience.

 

[IslandTractor]

I fully agree with Rob. 1/4 inch grapple arms will be too flexible and are likely to be damaged when grappling anything other than light brush. 3/8ths would be standard. Having said that, I suspect that the grapple arms on the PowerTrac 425 grapple bucket might be 1/4" (you'd need to confirm that) so with a relatively light duty set up (the PT425 has bucket lift of only 800lbs) you might get away with it.

 

[dtd24]

Done deal 3/8" it is. Still the welding of the flat stock question rather than plasma cutting sheetstock !!! Any input?

 

[KentT]

I fully agree with Rob. 1/4 inch grapple arms will be too flexible and are likely to be damaged when grappling anything other than light brush. 3/8ths would be standard. Having said that, I suspect that the grapple arms on the PowerTrac 425 grapple bucket might be 1/4" (you'd need to confirm that) so with a relatively light duty set up (the PT425 has bucket lift of only 800lbs) you might get away with it.

They're 3/8" unless I'm mistaken... yet, I've still bent the pointed end of one slightly by pinching logs and pulling them at an angle...

Not concerned about it enough to try straightening it -- in fact I think I've essentially straightened it out in use -- likely by pulling the opposite direction.

The pointed ends on the PT grapple arms aren't reinforced with any webbing or anything... there's only one crossbar, back about a foot or so from the end.

 

[3RRL]

Done deal 3/8" it is. Still the welding of the flat stock question rather than plasma cutting sheetstock !!! Any input?

Again, my opinion...
I don't think there's anything wrong with welding the flat stock together. Weld both sides and be sure you get excellent penetration and then grind the welds down almost flat. It should be as strong as the parent material. Since it will probably be harder and less ductile than the parent material in those areas, I would consider putting the cross braces right there, so they overlap the weld areas sort of perpendicular to the length of the weld beads.

 

[KAB]

I used 1/2 x 2 flat stock. (I could not pass on the price) I beveled the joints prior to welding and the ground them smooth. I used 15 degree angles (actually 1 more joint than I had planned but works quite well.)

It can be seen here. http://www.tractorbynet.com/forums/build-yourself/102733-another-grapple.html

Kurt

 

[3RRL]

Kurt,
I saw your thread and your welded jaws came out great.

 

[KAB]

Rob,

Thanks. That was actually the first time that I did any real heavier metal work. I used to do body work for a living, no heavy metal repairs there. I have spent a lot of time reading the welding forums trying to learn some of the tricks of the trade.

Kurt

 

[IslandTractor]

Rob,

Thanks. That was actually the first time that I did any real heavier metal work. Kurt

That makes it doubly impressive.

 

[SkunkWerX]

For what it's worth, I used 3/8" , and I agree with 3RRL, 1/4" is just a little too flimsy. If I had gotten "a deal" on some 1/2", I would have used it, for sure!

So far, after a couple hours of use, I don't see any un-due flexing or bending on the 3/8" welded stock. I took Pineridge's repeated advice about the gussets between the grapple forks, especially near the tips, and I do think it adds quite a bit of rigidity to the set-up.

Having the end jaws in-line with the bucket cylinder attachment points might make some sense, IF, that is also where the bucket has additional reinforcement?
However, I think the most stressed points in the entire equation are the grapple-cylinder mounts. The hydraulic force wants to spread the grapple away from the bucket, thereby pushing the mount backward, at the end attached to the bucket, and forward where it attaches to the grapple.

BottomLine, build it strong, but don't over-think it, it's pretty straight forward.