Simple Grapple Design done!

[polemidis]

Hello to the community. Finally I finished the design of my grapple. I made quite a few changes from my previous post -if you remember it-. I change the approach because right now its not easy for me to handle a full 3/8" sheet, and I do not want to give the cutting to someone else because of the cost. Its redesigned in a way that most of us can built it out of flat bar. A plasma cutter will definitely help for the hinges ,the multiple mounts, and the holes to the tines. The latter reduce the weight by around 30lbs, and when I run the FEM analysis it didn't show any significant difference between the whole tines and the tines with the holes.

The tines are 3/8", and the plates on the lids are gauge 10 (I feel its too thick??). Solid steel for pins. Without the 2.5" x 6" cylinders and the welds the total weight is 298lbs.

Clamping force at the closing position, starting with 2250psi is 2230lbs (2250*3.14*2.5^2/4*sin(14.91)*22/28)

Can you plz critisize it? Any comments, ideas, suggestions etc are welcome. Anything else that I may consider before I order the steel and start the fabrication process. I mostly need the negative ones, not trying to feed my ego today, rather than avoid mistakes :drink:
I know there is a lot of welding, but thats ok, I am just starting to weld I need practice.

Here is the current CAD feel free to download it and use it for any reason you feel like. Next week I will have the complete BOM at the same link.

 

[tvman]

Hello to the community. Finally I finished the design of my grapple. I made quite a few changes from my previous post -if you remember it-. I change the approach because right now its not easy for me to handle a full 3/8" sheet, and I do not want to give the cutting to someone else because of the cost. Its redesigned in a way that most of us can built it out of flat bar. A plasma cutter will definitely help for the hinges ,the multiple mounts, and the holes to the tines. The latter reduce the weight by around 30lbs, and when I run the FEM analysis it didn't show any significant difference between the whole tines and the tines with the holes.

The tines are 3/8", and the plates on the lids are gauge 10 (I feel its too thick??). Solid steel for pins. Without the 2.5" x 6" cylinders and the welds the total weight is 298lbs.

Clamping force at the closing position, starting with 2250psi is 2230lbs (2250*3.14*2.5^2/4*sin(14.91)*22/28)

Can you plz critisize it? Any comments, ideas, suggestions etc are welcome. Anything else that I may consider before I order the steel and start the fabrication process. I mostly need the negative ones, not trying to feed my ego today, rather than avoid mistakes :drink:
I know there is a lot of welding, but thats ok, I am just starting to weld I need practice.

Here is the current CAD feel free to download it and use it for any reason you feel like. Next week I will have the complete BOM at the same link.
View attachment 534635View attachment 534636

I am definitely no expert on grapples but I believe you will need to add a stop of some sort. This is to keep the grapple lids from going over center when they are retracted.Ask me how I know.

 

[polemidis]

I am definitely no expert on grapples but I believe you will need to add a stop of some sort. This is to keep the grapple lids from going over center when they are retracted.Ask me how I know.

Good that you bring that up. I was wondering if thats an issue since the angle between the lids and the cylinder at the opening is only 1.7°. Maybe make it a little more and sacrifice some of the force at the closed position, 2230lbs is too much anyway.
And I could design the top bracing plate of the lid to stop at the cylinder's base connection plates (the tall red ones). Thank you tvman!

 

[Rustyiron]

It looks good to me. I wish I had your computer/cad talents!

 

[Stomper]

I am definitely no expert on grapples but I believe you will need to add a stop of some sort. This is to keep the grapple lids from going over center when they are retracted.Ask me how I know.

****, im the last guy you should take advice from on grapple design, but wouldnt the position of the lid in the fully retracted and fully extended positions be built into the design with the location of the cylinder mounts as well as the cylinder travel length. This way there would be no need for a travel stop
Oh by the way, nice design. I like it

 

[tvman]

Stomper, you may well be right on this. I certainly don't have the skills or knowledge that polemidis has. When I built mine I found that when I was pushing the grapple into some heavy piles that the lid would double back on itself. I would also think It would help protect the cylinders.

I would like to see EA jump in on this, they are the experts.

 

[Joe Malovich]

I've attached a picture of some suggested changes that should be made for strength and crack-propagation reasons. Also some guys like their tine teeth to meet so they can pinch small offending roots/rocks. Source: I'm a mechanical engineer and amateur MS Paint user)

 

[polemidis]

It looks good to me. I wish I had your computer/cad talents!

14 months ago I didn't know what the CAD is Looking back now, you can reach my "skills" (its not skill, but just enough time spent working the program) one can reach that level in less than 100hours. Some tutorials, and someone to guide you is all you need. Feel free to ask anything about Freecad btw, I love it.

****, im the last guy you should take advice from on grapple design, but wouldnt the position of the lid in the fully retracted and fully extended positions be built into the design with the location of the cylinder mounts as well as the cylinder travel length. This way there would be no need for a travel stop
Oh by the way, nice design. I like it

It is that way. On the fully closed position the cylinder could extend the lid 2 inches more. But on the fully open position, I do worry that even though the cylinder ends 1.7° before the lid would turn the other way (backwards) thats not enough security. I can easy increase that angle and also make some mechanical stop. If you pay attension on the opened lid, it already touches the red anchor point of the base of the cylinder. Maybe thats some extra safety.

I've attached a picture of some suggested changes that should be made for strength and crack-propagation reasons. Also some guys like their tine teeth to meet so they can pinch small offending roots/rocks. Source: I'm a mechanical engineer and amateur MS Paint user)
View attachment 534656

You are right, do not make any holes at the brace points, and add a brace at the lid. Thank you!!! The teeth meet, yes.

If anyone wants the stronger version of this and can make cuts from 3/8" steel, on the link that I gave you above there is th link of my original design
I will update it soon. It looks like a open source grapple is 90% ready! I spent over 100hours redesinging, and changing stuff. Save some human efford, and improve mine rather than starting from scratch. Its my pleasure!!

 

[polemidis]

Suggested changes are done, clamping force now is about 2070lbs

 

[James Eric]

****, im the last guy you should take advice from on grapple design, but wouldnt the position of the lid in the fully retracted and fully extended positions be built into the design with the location of the cylinder mounts as well as the cylinder travel length. This way there would be no need for a travel stop
Oh by the way, nice design. I like it

Ditto....