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....

 

[GLyford]

Pins wear, travel does not always stay what it was at the beginning and design stages. A stop is cheap insurance.

 

[Stomper]

Another member posted this on another thread. I am looking at building one maybe. I like the simple construction of it.

MTL 48" XL Root Grapple Hydraulic Brush Grapple Attachment - Fits all mini Bobcat skid steers — MTL Attachments

 

[polemidis]

My apologies guys, I have not updated the site with the Bill of Materials and the final CAD. I got caught up with a snow plow.

But is very close to be ready. Glyford check this picture. Is not an actual deticated stop, but its some extra insurance. The plate that protects the cylinder and offers bracing now touches the cylinder base mount at the upright position. Would you agree with that? And the angle is 3.6deg. What do you think?
Also do you think that the green pins are ok like that or should I make them longer?

 

[rScotty]

Also do you think that the green pins are ok like that or should I make them longer?
View attachment 535314View attachment 535313

Yes, Make them full length. Easier to fab, line up, & secure. Over-constained is also a strength advantage.
But where is the advantage in using solid pins anyway?
Instead of pins, how about using 4130 weldable tubing? 1" dia. x 1/8" wall = $15/ft. 3/16 wall = $20/ft.
Or since pins are short, with low stress, and large diam. is OK... how about black iron water pipe instead of pins?

 

[GLyford]

One word: wear. Look at some of the youtube vids of people rebuilding backhoe pins, machines often have an amazing amount of wear before someone gets fed up with it enough fix it. Sometimes they won't stop using a machine until they have literally started ripping it apart (pulling the bushings out through the structure). Going with a solid pin is cheap insurance for that, as opposed to Sch40 or 1/8 wall tube.

As to letting the arm structure bump the cylinder mount, I suspect you will be okay, with one proviso...are you planning on any kind of sheet metal cover over the cylinder? Grapple means operating in brush, with sticks and branches pointing every which way. They can get into the darnedest places and damage hoses, or get into pinch points like that and stop the motion before you expect them to (while the cylinder still has leverage) and then maybe break something. So as long as you have a reasonable expectation that if someone rams a brush pile to get a bigger bite the linkage areas and hoses are mostly covered, I think you will be OK.

 

[GLyford]

Another way to help with wear:
Make it EASY and OBVIOUS to get grease to the pins (either drill the bushing for a zerk, or drill your pins from one end to the middle, then cross-drill).

 

[jclaudii]

I'm not an expert and don't have a grapple as my caveat, but you may want to add some more flat bar for support and strength in key areas.

1st, I would like to see a center "ridge" on grapple out of flat bar. Down the spine where the cylinder is and on the front part facing down. It can be on the inside and could give things some more grip when it digs in.

2nd, lateral bracing. That seems like a long stretch between the rear of the bottom mount to the round stock that ties it in to where the teeth are. I would strongly consider adding in some slanted flat bar in direction of penetration like =o=o=\=o=o=\==- This would help prevent the tines from spreading and rock/root/stick from wedging in between the tines. It will also make it quite a bit stronger for deflection or off center approach. I would add at least one more flat bar brace on the back of the tool too.

3rd, double up on the outer most tines to make them twice as thick and the center most tine/tines. just cut out a few extra tines and weld them to each other to double your thickness of material in those locations. As I see it now it would be more likely to bend in its current state than to with the extra material on the edges and center. You would get good welds with the holes you have as well.

Think hitting a root while going forward and just skimming it on the righter outer most tine which causes the whole tractor to be deflected to the left. That is alot of weight and momentum that was absorbed by throwing the tool and the machine to the left. Or backing up and take out a small tree with the tine...done that with the bucket before. I think you have it down to where it will function as intended, now step away and think about how you could use it in a way it was not designed for or accidentally or purposely doing something that could damage it. Looks cool.

How are you doing the hydraulics?

 

[rScotty]

One word: wear. Look at some of the youtube vids of people rebuilding backhoe pins, machines often have an amazing amount of wear before someone gets fed up with it enough fix it. Sometimes they won't stop using a machine until they have literally started ripping it apart (pulling the bushings out through the structure). Going with a solid pin is cheap insurance for that, as opposed to Sch40 or 1/8 wall tube.

I've never designed anything specifically for deliberate abuse. But how do you figure that going to a solid pin offers more wear resistance than the thin wall bushing that it runs in? How thick should the walls of the bushing be? Which wears most? The bushing or the pin?
rScotty

 

[polemidis]

I've never designed anything specifically for deliberate abuse. But how do you figure that going to a solid pin offers more wear resistance than the thin wall bushing that it runs in? How thick should the walls of the bushing be? Which wears most? The bushing or the pin?
rScotty

The reason that I went for solid pin is mostly wear, and because the outer diameter is exactly 1", with the thick pipe that serves as bushing being a few hundreds over 1" internal dimension. The flat piece that is welded at the end of the pin has a small hole for a 5/16" bolt, so be removing that bolt I can take the hole thing apart and grease it. Its not as easy to grease as a zerk, but since no water can penetrate in there I believe I will be ok to do it whenever I service the tractor.

Jclaudii, about the hydraylics, I will "T" the cylinders to work in parallel. So they can grapple to different angles if the load is uneven. They will be controlled by the 3rd function.

On the other comments give some time to think about them. Or can someone give me some numbers to add to the Finite Element MAterial Analysis? I am learning to work with that tool, but I do not know what stresses to test for

 

[GLyford]

The first thing a non-greaseable pin will do is rust, jam, or gall in the hole preventing disassembly without large amounts of jacks, chains, big hammers, torches, mashed thumbs and swearing. Ask me how I know. Do not rely on any lubrication method that requires disassembly of parts to add lubrication. If anything, lube parts while in place to aid in disassembly when needed.

I don't know the metric numbers off the top of my head, but for 1/4-28 zerks, you drill in from the end 7/32, then tap 1/4-28 (fine thread). Drill crosswise through the diameter to intersect inside the mechanism, can be any size from 1/8 to 1/4". Be careful of the bit catching and breaking when it intersects the other hole. If the pin is mild steel, it is very easy to do.