Need info on steel strength

[ns_in_tex]

I have built a root rake grapple and used 1" steel rod for the hinge. It is spanning 5" with the grapple attachment made of 3/4" steel plate, centered in the 5" and is operated by a 3" dia cylinder.

It seems to hold the hydraulics OK, but I hung the grapple on a tree & it bent the 1" pin a little, but not beyond use. It also blew a hydraulic hose at the same time.

So when I decide to replace the pin, I will want to try to make it stronger. Because of the pivot clearances, I do not want to go to a larger pin.

So what are your suggestions?
Would heat treating the pin make it stronger or just harder?
Or would it be better to try to close in the 5" span?

Thanks for any suggestions?

 

[jmc]

Neal,

Definitely close up the clearance to a minimum. With no clearance, the pin is in pure shear-very strong. More clearance means shear plus bending stress. Heat treating is better than nothing but you need to know what the metal alloy is and pick a medium hardness to avoid brittle failure. Only some alloys can be hardened full thickness. Mild steel can be case hardened(surface) only and probably won't gain much in strength.

Got any pictures?

John

 

[markct]

well its kinda hard to picture just how its setup but i assume you mean that in the center of the 5 inch span the 3/4 thick plate thats the grapple is welded to this piviot pin and then its just open air to the 5 inch opening, could you weld gussets in this space, also closing the 5 inch opening would help alot since a pin is always stronger in shear than in bending. also what material is your pin made of, just mild steel? something like case hardenened shafting, or 304 stainless would be much tougher, or possibly an old truck axleshaft machines smooth on a lathe, they make an extremely tough pin but are very hard to machine but they are about the ultimate for toughness a picture of what you made would definatly get some more insight tho on how to improve this setup

 

[mrcaptainbob]

Can't quite picture exactly what it is that you have except that you have 3/4" centered on a 5" span of 1" round stock and it bent the round stock and blew a hydraulic line. It's the hydraulic line coming apart that bothers me. That may well asnwer why that 1" pin bent. Did the relief valve not work? What caused that hose to pop? Had to be either a weak spot or too much pressure. Heat treating would harden that pin, but may not be the answer.

 

[ns_in_tex]

Thanks, John & others,

I will try to get a picture tomorrow, of the hinge setup.

I only used it today for the first time for about an hour.

I think, probably the pin was mild steel. Made them out of an old blower shaft.

I don't think the relief bypass in is the circuit when a valve is not open. I have popped hoses before by putting to much pressure on an implement, while pushing to hard on something. Like I was in low range, 4 wheel drive, differential locked, ETC while not realizing the grapple had hung on a tree.

I am hoping to get any bugs out of it, and maybe a coat of paint, before posting pictures of the whole implement.

 

[bgott]

You can make your pin out of a torsion bar from an old Chrysler product. According to a blacksmith book I have they're made from 5160. I don't know how long they are, you might have to weld two together.

 

[hazmat]

<font color="blue">So what are your suggestions?
Would heat treating the pin make it stronger or just harder?
Or would it be better to try to close in the 5" span?
</font>

For a beam (your round stock) supported on both sides the bending moment is directly proportional to the length ie 1:1. the amount of stress you can handle is proportional to the moment of inertia (cross section) and material strength.

Given that you want to keep the pin the same size, both shortening up the span or increasing strength of the steel will help. ie - @2.5" ILO 5" you could handle 2X the load. @2X steel strenght you could also handle 2X the load. Maybe a combination of both.

A word on inertia: For a circular section I = pi*diameter^4/64. It is diameter to the 4th power. Big bang for the buck here.

A 1.25" pin would be 2.44 times stronger. A 1.125" pin would be 1.6X stronger. A 1.5" pin would be 5X stronger. Maybe you want to re-evaluate changing pin size?

Good luck & I wish I had the fabrication tools to build half the projects you've shared with us.

 

[SPIKER]

if you bent the pin and blew the hose, then I would say that you hit soemthing pretty hard to do that. like others said close the gap, between the opening, so there is more shear stress and less bending stress. or increase pin size, (maybe not an option for the HYD cylinder? remember next time it happens it may be more than just a bent pin/blew hose, maybe broke act? but I would think that adding a relife valve would help a lot as a break away device to HELP prevent the next time...

markM

 

[PineRidge]

<font color="blue">I think, probably the pin was mild steel. Made them out of an old blower shaft.
</font>

Neal most blower shafts were indeed cold rolled, ground, polished, and surface hardened only. They can be very easily cut using a hacksaw.

 

[ns_in_tex]

Attached is a picture of the hinge.
I can add some metal inside the uprights, but must leave enough room for the cylinder end (horseshoe) to pass between.