Will this hold or crack over time? Do more passes?

   / Will this hold or crack over time? Do more passes? #61  
For example....

2x2x1/4 tube has a moment of inertia (i4) of 0.745

2.5x2.5x1/4 is 1.63.....which means it over twice as strong.

3x3x1/4 is 3.02....which is more than 4x as strong as 2x2 and almost twice as strong as 2.5" square tube.

Stress formula is the distance to the center axis (half the tube size) times the force times the length in inches.......all of that divided by 4 x moment of inertia.

So if you span 36" with 2x2 tube....and apply 5000# of force.......

(1x5000x36) / (4 x .745)= the stress on the member. About 60,000psi....which likely exceeds the rating of the tube. Most tube is 50ksi

If you used the 2.5" X1/4 wall tube....with 1.25" center distance and i4 of 1.63.....

(1.25 x 5000 x 36) / (4 x 1.63) you are down to 34.5ksi stress.

The 3" tube would drop to 22ksi stress.

Can also factor deflection.....the force times the weight cubed.....dived that by 48 times the i4 times the modulus of elasticity constant. (29,000,000)

So for 2" tube
(5000 *36^3) /(48x29,000,000x.745)

Your tube will flex about 1/4"
2.5" tube would be about 1/10th of an inch
3" tube would be about 1/16th of an inch.

Hope I didn't loose you. But that's the crash course on stress and deflection and how to apply it. Of course you may be spanning more than 36" or less. And you may be applying more than 5000# or less.

But span.....force....and the moment of inertia are what you can look at, at a glance and get a feel for how strong something will be with just a few calculations.

The strength of that round bar you propose adding.....1.5" only has a moment of inertia of 0.24

So even 2" tube with round bar added is not even close to the strength of 2.5" tube.
 
   / Will this hold or crack over time? Do more passes? #62  
I tried to find a load calc. There was one I used…. span of 44”, middle 3rd, tortional stress from 2000lb and came up with like 21,000lb. No ideal if it was a correct type of calc cause it doesn’t take into the leverage.
Took me awhile to type that last reply so it didn't take into account this last post of yours.

Your proposed design with TWO tubes connecting the latch boxes...I don't think torsional strength is a huge concern. More just the point load at midspan between the two latch boxes.

But in either case.....your strength, both stress/deflection AND torsion come from getting material FARTHER away from the central axis. IE: larger size tube.
Adding mass (like round bar inside tube) gains you very little. Adding mass AWAY from the central point is where the money's at
 
   / Will this hold or crack over time? Do more passes?
  • Thread Starter
#63  
Thanks, and I do understand basically. Kinda. there is also the 2.5” x 1/4 round tube there from the factory, likely a better grade of steel than the mild steel I have.

my second ideal was to go with the square tube but add 1/2 plate to it, this pic kinda shows it. The first pic is the 2 orange ears with the blue tube, second pic shows the yellow 1/2” plate completely welded to tubes. 3rd pic is the side view. I’ve got a36 and ar500 1/2 plate. The green represents the way I see force being applied with pallet forks.

060AFDCE-FE48-467A-9930-56D2BCACBCE5.jpeg

Trying to keep it as light as possible with no engineering knowledge is difficult.
 
   / Will this hold or crack over time? Do more passes? #64  
Here’s a spartan one. It looks like they only used a single tube. Would like to know what grade and what thickness. The angle they did will work great for attachment facing the excavator but will almost be useless for using facing away. You would have to extend boom out pretty far to get whatever you have attached like forks level. But doing a bolt on does give the ability to reverse it.
View attachment 755974

I saw that bracket after I was looking for images after you made the first post. One good part about that design is the tube isn’t spanning very far. It’s probably only 10” or so if even that much.
 
   / Will this hold or crack over time? Do more passes?
  • Thread Starter
#65  
I did call spartan, that tube is grade 50.
 
   / Will this hold or crack over time? Do more passes?
  • Thread Starter
#66  
I picked up a peice of 4x3x5/16 tube. This is roughly the angle. I have 2 ideas how to further brace it From back of adapter to bottom of ssqa.

A3E1B06F-7A99-43D4-B6B3-64E3E01ABF0C.jpeg
8101EFC6-B7FB-4497-9AD8-863CD3970978.jpeg
 
   / Will this hold or crack over time? Do more passes? #67  
That's gonna be under a lot of torsional stress. That looks nothing like your earlier sketch.

And I'd never want to make something where the machine can self destruct itself. And that headache rack on them pallet forks is gonna trash your bucket cylinder if you tilt the forks back too far
 
   / Will this hold or crack over time? Do more passes?
  • Thread Starter
#68  
Lol. Just showing how it’s attaching. Still will be bar at bottom and gussets coming to rear.
 
   / Will this hold or crack over time? Do more passes? #69  
Lol. Just showing how it’s attaching. Still will be bar at bottom and gussets coming to rear.
Are you worried about the pallet fork backstop hitting the bucket cylinder?
 
   / Will this hold or crack over time? Do more passes?
  • Thread Starter
#70  
Yea, was just making sure of clearance. But that’s how it needs to be mounted and I have to build from there.
 
 
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