Anything welding

Anyone can over engineering a product

 

Most programs tell you the recommended material thickness needed. I know my vendors programs do

 

The 1/2" material used on the recovery point isnt what sketches me about it, it's the proximity of the D ring through hole to the front of the recovery point. Looks like it gets pretty thin up there, I know I wouldnt want to see it tear open and send a D ring flying on the end of a strap/cable. JMHO, but I would at least weld on another piece on the side to laminate the material and make it a bit thicker... or sleeve some tube through the hole if the diameter of the hole is large enough to do that and still hold a D-ring.
Remember, static and dynamic forces are much different. In a static load situation sure maybe(probably) it would be fine. But then add in the 'tug' of a recovery which shock loads the material and you may see failure. Plus with a shock load like that that would give the recovery line the most stretch and stored energy to send the projectile(d-ring) flying and could do some serious damage. My $.02

 

Yes, this is something that Solidworks will do when designing parts and doing stress analysis on the part

 

Totally agree with that, too.

Going to do some destructive testing on Amsteel and some other synthetic rope sometime in the near future.. Got an invitation from the lead engineer at Samson. It'd be pretty cool to test a recovery point/shackle/winchline combo; not sure if it'll for on their test bed.

 

OK there you go, so maybe some 1" .120 wall tube for a sleeve and run a quality 5/8" US made shackle. You'll see american shackles with a higher load rating than the chinese ones. my US made 3/4" are 6 1/2 ton rated rather than the 4 3/4 ton rating on the common chinese ones.

 

This ^^^

It's crucial to understand the difference between WLL/Breaking Strength/Safety Factors..

Also, something really cool is how exactly the lifetime of a length of synth. rope is calculated. Cycling/shock loading/over-stressing, etc.

 

For instance, this 5/8" is 4 1/2 ton rated with a 5:1 safety factor... 45,000lb catastrophic failure. Probably going to rip the truck in half at that point. lol
http://www.fastenal.com/web/product...pcode=&filterByStore=&filterByVendingMachine=

 

To me over-engineering means building it bigger on the assumption that it's going to be better...

I agree with you on what you've said. I feel like having solid engineering with home fab projects is just as important as having it look "cool". I've been around pad eyes when they've failed due to shitty design. Not fun. Especially with 25 Tons at 50' overhead.

 

I have to agree with Jason, I've seen smaller mounts like that rip before.

 

Sleeve it w/stainless.. Because the insides of your mounts are bound to get the paint rubbed off by shackles..

 

I always use the 7/8" d-ring mounts

Built this bumper for a friend last weekend and used them

 

I'm with Eric and Jason on this as well. 1/2" would be fine if your hole wasn't so close to the edge I can see that ripping open in a hard pull. Same go's with surface welded shackle mounts (not that you did that) I will not pull from them on the trails they are on their own. There is a few companies that just weld them to the outer skin of the bumper and it's a big no no in my book. I know what ones have them and I refuse to pull from it.

That said my shackle mounts are 1" cold rolled through welded to 2" x 3" x .188 wall tube.

 

Personally I would.

 

My mig is setup for .030 wire and I want to weld my sliders to my frame. Will this work or should I run .035 wire?

 

.030 is totally fine

 

Kase, the allowable stress of mild steel is 36,000lbs/square inch. For shear stress you have to divide that number by a factor of 2. So you have an allowable stress of 18,000lbs/square inch. More than likely your failure mode (past bending) will be shear pull out. Meaning that the slug of steel that's holding the pin of the shackle will shear away.

Like this...


You have to take into account the area of steel on either side of the area that could pull out.

It looks like the length of your shear plane is about 1/2". Here's how we find out the pull out strength.

F = allowable stress * 2 * l * t

F = pull out force
2 - (because we have two shear planes to consider)
l = length of material in shear (1/2")
t = thickness of the plate (1/2")

F = (18,000lbs/square inch) * (2) * (1/2inch) * (1/2inch)

F = 9,000lbs


So at 9,000lbs of STATIC load you will pull the shackle out of the eye.

Here's the kicker. Lifting eyes typically have a safety factor of FOUR, so you only have a safe working limit of 2,250lbs for that particular eye.

You will also see much higher loads under dynamic loading conditions. Meaning if you're trying to snatch someone out of a hole you'll definitely rip the shackle loose.


Here's what you can do to solve this problem.

You need to add cheek plates around the hole to increase it's thickness. Figure out which shackle you will be using and find it's throat opening width. Subtract off 1/8" and that will give you how thick of a cheek plate you can weld on.




Other things to consider

Don't forget that most bumpers tie the bumper back to the frame with a plate on either side so they're not relying strictly on the tensile strength of the mounting bolts.

When you cut the holes in the plates for the shackle you need to consider the size of the shackle pin. The hole should be 1/8" larger in diameter than the pin diameter. So a 3/4" shackle, which has a 0.88" diameter pin, should have a hole diameter of 1.0". Looks like you got that one right.

A 3/4" shackle has a throat of 1.25". That means you can have a 5/16" thick cheek plate on either side of the 1/2" eye. I'm assuming that you won't have 5/16" laying around, so use 1/4" plate. By adding two 1/4" cheek plates to either side of the 1/2" plate you'll increase your pullout strength to 18,000lbs. Throw in the safety factor of 4 and you're at 4,500lbs. You can probably be safe with a SF of 2 instead of 4, so let's say your pullout strength will be 9,000lbs.

You'll still bend the plate if you side load it though. Good luck.

 

He's trying to give you some advice with practical examples. He's right too.

He could have added that a lot of guys fab their recovery points with a "T" at the back side and install them through the bumper with welds on the front and back. This spreads the load more efficiently through the bumper.

The absolute worst thing that could happen isn't ripping the bumper off. It's tearing the tab off and having it fly back at the anchor point