PSA: Check your recovery points

To nerd a little.
Screenshot_20231008-203549.png

This is what Google found for a force calc. I used 6k and the feet per second is roughly what 15 mph come to.
 
So roughly 2 tons of force applied if I'm not an idiot and using the wrong formula.
Then I found this and was really interested.
Screenshot_20231008-204453.png

I used the circumference on the 1.25 tube and called it a 1/8 fillet. Actual weld measured sized is probably more.
Then I did a basic average of A36 steel. Plain mild steel strength nothin special. I assumed a ER70 type mig filler was used. As tested 70k strength in the weld wire....blah.
So I just averaged half the difference between base metal and filler to arrive at the diluted weld strength.

Now the calc in the pic should be for one side.

My math isn't matching or one of two things have happened.

Lots of woooooopow hits on that loop, lots of over all fatigue and what I refer to as repetitive blunt force fatigue(I like hammers) or the reality that weld strength is highly subjective because of many factors. The latter of which I'm well aware of but geeze that's a big number difference.

One side of that connection irks me without pause....the other tear out and what appears to be the base metal around the entire weldment is another.

All this to say damn.....
 
WARRIORWELDING said:
So roughly 2 tons of force applied if I'm not an idiot and using the wrong formula.
Then I found this and was really interested.
View attachment 404814
I used the circumference on the 1.25 tube and called it a 1/8 fillet. Actual weld measured sized is probably more.
Then I did a basic average of A36 steel. Plain mild steel strength nothin special. I assumed a ER70 type mig filler was used. As tested 70k strength in the weld wire....blah.
So I just averaged half the difference between base metal and filler to arrive at the diluted weld strength.

Now the calc in the pic should be for one side.

My math isn't matching or one of two things have happened.

Lots of woooooopow hits on that loop, lots of over all fatigue and what I refer to as repetitive blunt force fatigue(I like hammers) or the reality that weld strength is highly subjective because of many factors. The latter of which I'm well aware of but geeze that's a big number difference.

One side of that connection irks me without pause....the other tear out and what appears to be the base metal around the entire weldment is another.

All this to say damn.....
Click to expand...
I'm no engineer, but my bet is if it was welded to a thicker parent metal, it wouldn't tear. But, that's a shitload of force on two welds distributed around 1.25" tubing.
 
I think the main issue was the mounting angle. That put a nice twisting load on it, which was made worse by the poor penetration on the left side. I’m guessing the left side failed first, and then you can see where the right side sheared cleanly along the weld line at the bottom first, then tore out at the top as it ripped away from the tube.
 
justjeepin86 said:
I'm no engineer, but my bet is if it was welded to a thicker parent metal, it wouldn't tear. But, that's a shitload of force on two welds distributed around 1.25" tubing.
Click to expand...
Parent material thickness would help for sure on the side that tore out.
Here is another thing to chew.
Look at this generic mount.
Screenshot_20231008-211741.png

It allows for 7.6 inches of weld over the circumference. At the same fillet we get...
Screenshot_20231008-212347.png


A substantial difference. So without looking just a equal size tube as the base would help.

Also I'm not disputing or placing blame just nerding a little on numbers.

As @jeepinmatt said angles and such play hugely into to equations. My over all take is just like the original from @CLRracer check your points and really consider how they are executed.

Even the surface mounted clevis mount I used for comparison is plain dangerous loaded over and over, welded poorly, and Yanks at wanky angles.
My grampa said it best:" It's damn wonder any of us live as long as we do."
Referring to life in general.
 
WARRIORWELDING said:
Lots of woooooopow hits on that loop, lots of over all fatigue and what I refer to as repetitive blunt force fatigue(I like hammers)
Click to expand...

This definitely happened. We were using a 20 or 25ft rope and he was backing up at least half of the length a few times, plus another vehicle pulling him. Up some steep, loose terrain. Admittedly not ideal recovery conditions, and I honestly expected the rope or soft shackle to fail if anything.

Duane
 
CLRracer said:
This definitely happened. We were using a 20 or 25ft rope and he was backing up at least half of the length a few times, plus another vehicle pulling him. Up some steep, loose terrain. Admittedly not ideal recovery conditions, and I honestly expected the rope or soft shackle to fail if anything.

Duane
Click to expand...
To bad those ropes are not manufactured as a "fuse". The general public would get all pissy about cheap tow straps and never realize the safety of such.
 
CLRracer said:
This definitely happened. We were using a 20 or 25ft rope and he was backing up at least half of the length a few times, plus another vehicle pulling him. Up some steep, loose terrain. Admittedly not ideal recovery conditions, and I honestly expected the rope or soft shackle to fail if anything.

Duane
Click to expand...
I let freedom ring a few times! In retrospect, checking recovery points before is great, but should also be checked periodically during recovery, when all the horsepressures are being used in multiple short bursts.
 
WARRIORWELDING said:
To nerd a little.
View attachment 404813
This is what Google found for a force calc. I used 6k and the feet per second is roughly what 15 mph come to.
Click to expand...
WARRIORWELDING said:
So roughly 2 tons of force applied if I'm not an idiot and using the wrong formula.
Then I found this and was really interested.
View attachment 404814
I used the circumference on the 1.25 tube and called it a 1/8 fillet. Actual weld measured sized is probably more.
Then I did a basic average of A36 steel. Plain mild steel strength nothin special. I assumed a ER70 type mig filler was used. As tested 70k strength in the weld wire....blah.
So I just averaged half the difference between base metal and filler to arrive at the diluted weld strength.

Now the calc in the pic should be for one side.

My math isn't matching or one of two things have happened.

Lots of woooooopow hits on that loop, lots of over all fatigue and what I refer to as repetitive blunt force fatigue(I like hammers) or the reality that weld strength is highly subjective because of many factors. The latter of which I'm well aware of but geeze that's a big number difference.

One side of that connection irks me without pause....the other tear out and what appears to be the base metal around the entire weldment is another.

All this to say damn.....
Click to expand...
WARRIORWELDING said:
Parent material thickness would help for sure on the side that tore out.
Here is another thing to chew.
Look at this generic mount.
View attachment 404822
It allows for 7.6 inches of weld over the circumference. At the same fillet we get...
View attachment 404823

A substantial difference. So without looking just a equal size tube as the base would help.

Also I'm not disputing or placing blame just nerding a little on numbers.

As @jeepinmatt said angles and such play hugely into to equations. My over all take is just like the original from @CLRracer check your points and really consider how they are executed.

Even the surface mounted clevis mount I used for comparison is plain dangerous loaded over and over, welded poorly, and Yanks at wanky angles.
My grampa said it best:" It's damn wonder any of us live as long as we do."
Referring to life in general.
Click to expand...


Imma just say I don't know if what you're saying is English or not, but the math talk is moistening my manties.


Also glad OP is good to go.
 
Excellent welds or not, your base and hoop metal is just 1/8” thick. Unless specifically designed and engineered, I wouldn’t use 1/8” metal for recovery. This isn’t picking on this one incident, it’s a generalization of my overall opinion. If I were stuck, would I accept help from the rig with the failed hoop? Sure would.

Thankfully nobody got hurt and we all can learn so it doesn’t happen again. Next time we may not be so lucky.
 
As everyone else has said, glad no one was hurt. But I'm glad you brought attention to this. Recovery points and recovery operations are serious business and need to be treated as such.
Check your equipment regularly for wear and fatigue. Treat every recovery carefully and with the proper respect.
 
Holy fuuuuuuu
Glad no-one was hurt.


If you want a couple of ideas
As far as making another tow point, just cut the bar, replace it with a 1.75x .250 unit and use a soft shackle to go around it.
The math gives you about 5k of force as a center point load (worst case scenario) before it enters plastic deformation. Still not ideal.

I'd suggest a couple of corner gussets and doubling the shackles so you can spread the load better. See below, imagine it's a view from above :

1696858775246.png

Black is 1.75x.120 tubing
Blue is 1.75x.250 tubing
Red is towing force. I know the scenario 2 would have the arrows pointing more towards the inside, like a triangle.

Scenario 2 probably doesn't even need .250 tubing since most of the force is focused close to the ends of the material.
 
Bebop said:
Holy fuuuuuuu
Glad no-one was hurt.


If you want a couple of ideas
As far as making another tow point, just cut the bar, replace it with a 1.75x .250 unit and use a soft shackle to go around it.
The math gives you about 5k of force as a center point load (worst case scenario) before it enters plastic deformation. Still not ideal.

I'd suggest a couple of corner gussets and doubling the shackles so you can spread the load better. See below, imagine it's a view from above :

View attachment 404842
Black is 1.75x.120 tubing
Blue is 1.75x.250 tubing
Red is towing force. I know the scenario 2 would have the arrows pointing more towards the inside, like a triangle.

Scenario 2 probably doesn't even need .250 tubing since most of the force is focused close to the ends of the material.
Click to expand...
If you put large tube gussets close to the center of the tube on scenario 1, then you will have great support transferred to the adjacent tubes and greatly reduce the risk of bending the horizontal tube.
 
tobaccoroad4wd said:
@ghost
My rig. My tow point.

@CLRracer came over the radio, rig was dead at the entrance of Rubicon. The obvious answer, that many of us have and will continue to do is go help.
Got down there and got hooked up and I gave her hell trying to get traction pulling up the trail to get him out. We ended up hooking @Mrxdieselx YJ to me, and essentially had an offroad train chugging up the trail.
We made it a good ways up, before the loop left the chat. It’s an absolutely horrible feeling, and a horrible sound. I’ve seen seen some videos back in the day, of guys getting cut, hurt and worse and the sound of metal tearing and cracking at the same time, is one I do not ever want to hear again.
The loop was 1.25”, .120 DOM welded to 1.75”, .120 DOM.
I’ll state this for clarity, I did not weld it; Not saying I’m a professional, or that mine could or would have been better, I’m saying it because I can’t get the sound out of my head, nor the feeling of ‘what if,’ especially when a friend and his family are in the rig being pulled. After it happened, and everyone was ok, I left to go find Bobby and the dozer to pull him the rest of the way.
View attachment 404809
View attachment 404811
View attachment 404810
Click to expand...
Thanks for posting this. Defiantly learned some things here.
 
rockcity said:
If you put large tube gussets close to the center of the tube on scenario 1, then you will have great support transferred to the adjacent tubes and greatly reduce the risk of bending the horizontal tube.
Click to expand...
This is my intention.
I have several plans for the near future, for a few things I want to change. And the rear section of the buggy just got bumped up on the list.
 
Bebop said:
Holy fuuuuuuu
Glad no-one was hurt.


If you want a couple of ideas
As far as making another tow point, just cut the bar, replace it with a 1.75x .250 unit and use a soft shackle to go around it.
The math gives you about 5k of force as a center point load (worst case scenario) before it enters plastic deformation. Still not ideal.

I'd suggest a couple of corner gussets and doubling the shackles so you can spread the load better. See below, imagine it's a view from above :

View attachment 404842
Black is 1.75x.120 tubing
Blue is 1.75x.250 tubing
Red is towing force. I know the scenario 2 would have the arrows pointing more towards the inside, like a triangle.

Scenario 2 probably doesn't even need .250 tubing since most of the force is focused close to the ends of the material.
Click to expand...
I have the same chassis you do, just an earlier version. A few changes are in the works, some I will do myself, some done by @MarsFab
 
tobaccoroad4wd said:
I have the same chassis you do, just an earlier version. A few changes are in the works, some I will do myself, some done by @MarsFab
Click to expand...
Hell yeah ! Chris does metal magic, can't wait to see the result.

My rear section is a little bit different due to trailing arms and the high uptravel numbers but it has a similar tube that I've used for light recoveries. Never trusted it for heavy ones and this confirms it.
I have used the rear axle as a heavy tow point a few times but I ended up ripping the truss off at some point (not while towing though, happened on a waterfall) so not ideal either.
 
WARRIORWELDING said:
Lets say all of the "science of metals" was 100 percent. I'd love an engineer type to chime in with the cross section tensile strength of said weldment. Let's make it easy with the know circumference of the tube and use a cross section of weld equivalent to the size of a fillet expected of 1/8 of an inch.
Any of you modeling engineer type able to calc the strength in a perfect world and a straight line pull?


I'd love to see that damage up close. Glad everyone is good!
Click to expand...

Edit- didn't see all the other posts, saying same thing I did lol. Guess I should have read the whole thread.

I'm by no means an engineer, and your welding knowledge likely far exceeds mine. But from my time running calcs and designing fabrications, I would say a 1/8" fillet weld all around on those two points would have a substantial shear rating (14.8 kips based on quick math while eating supper).

From what I can see, it looks like the weld failed at the hoop on the left side and then the base pipe actually sheared on the right. Not knocking anybodys welds (it held on the right side, the material failed), but maybe it didn't get tied in well? Whole lotta stress induced at an odd angle and in one specific point.

Maybe I'm just talking out of my rear end, it's been a long day and I'm tired.

Also, I'll say that I wouldn't have doubted that recovery point. Hate it broke and glad everyone is alright.
 
Last edited:
Back
Top