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Union Fab Works
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Discussion Starter #1 (Edited)
This has been discussed a bunch, as i just read quite a few threads on it, but i need some opinions on my personal selections here.

I'm doing 4 link front and rear. My original thoughts were 2.0/.500 for the lowers and 1.75/.375 for the uppers. This seems pretty stout. I trust the lowers, i know people are bending this stuff, but It will work for a while at least, and i'm not as heavy footed as Dibble. close, but not quite.

But, my weld on JJ's i'm using have only a 2" wide surface on the shell. This will make for a hell of a task to weld a 2" wide piece of tubing to it. How does everyone feel about this. I guess i could chamfer the edges where the tube will meet the joint body but I'm afraid i will lose strenght with as much as will to chamfer off to fit a mig bead in there. Other option is to have them tig'd, but even then will be difficult.

So, do i switch out my 2.0/.500 lowers for 1.75/.500 lowers. Is this that much stronger than the 1.75/.375 i have for the uppers. This would give me an 1/8" all around the steel to allow me to weld to. But, I have a guy in our club here that bent a 1.75/.500 link already, so i'm leary.

So suggest some link material for me here... I need to decide something immediately.
 

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i use 7075 aluminum...it holds up well, in the 1.75" variety on top and bottom. Some use 2" on bottom, but my lathe won't hold 2", so im stuck with 1.75 until i get a steady rest. I have only "wasted" on link (big bend) ever, in 4 years of ridin around on aluminum linked stuff.
 

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thhhpptthh!
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carwash said:
I would love to use aluminum, but I'm not running any adjustments, so my JJ's are being welded directly to the link, and they are of course mild steel.

weld a bolt to em.
 

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The difference in bending strength between 2" .500 wall and 1.75" .500 wall is huge. The 2" has a moment of inertia of .736 compared to the 1.75"s .445. This means that the 2" is roughly 1.6 times as strong, in bending, compared to the 1.75, assuming all other properties are the same. What are your chances of using a thread in joint instead so you can use a larger OD tube?
 

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chamfer them and then make two gussets that lay on the tube and wrap around the jonny joint should be solid
 

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Union Fab Works
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Discussion Starter #9
typo

Flashover Mfg said:
Yes, 1.75x375 is stronger than 1.75x300. You can use this calculator to compare any size that you want. The higher the moment of inertia, the stronger in bending the tube will be.
Crap, i meant .500, not .300. Thanks for the link to the calculator. Also just found out that the link bent on my buddy's rig is 1.5/.500.
 

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ill be that guy this time-square tube! 2x2 .250 wall and you can either weld on some all-thread or maybe a piece of 1.5 OD and weld that to the jj and into the tube.
 

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Union Fab Works
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Discussion Starter #12 (Edited)
Wow, very cool calculator... here are some popular "Moment Of Inertia" numbers so we can all look at them...

1.5/.120 = .125
1.5/.250 = .199
1.5/.375 = .233
1.5/.500 = .245

1.75/.120 = .205
1.75/.250 = .341
1.75/.375 = .411
1.75/.500 = .445

2.0/.120 = .314
2.0/.250 = .537
2.0/.375 = .666
2.0/.500 = .736

2.25/.120 = .457
2.25/.250 = .798
2.25/.375 = 1.01
2.25/.500 = 1.138

2.5/.120 = .637
2.5/.250 = .132
2.5/.375 = 1.457
2.5/.500 = 1.669

Crazy to look at it that way. Nuts to think that .250 wall 2.0 is 25% stronger than a .500 wall 1.75 tube. Crazy.
 

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That's actually not a bad idea. You really need the bending strength (large cross section) at the center of the link, not nearly as much at the end. If you are willing to put in some work, I think a piece of 1.5x.250 at each end attached to a piece of 2.25x.375 for the center would be really strong. I would probably make each the smaller tubes about 15-20% of the overall length of the link and the remaining 60-70% the larger OD. Make sure that the small tube is slid a couple of inches into the large tube so you can get some good rosette welds on it in addition to the fillet weld at the transition point.
 

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Union Fab Works
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Discussion Starter #14
I guess with the MOI gain i get with .500 wall 2.0 DOM, it's worth it to chamfer the corners of the tube so that they can be welded on.

How do we feel about this? It will only be for a section about an 3/4 of an in long or so on the sides... shouldn't compromise strength too much i don't think. What do you all think?

I guess i just really want to use the .500 wall for piece of mind...

But here is another question... is a MOI of .445 of the 1.75/500 wall pretty damn strong as well? I don't know how to gauge the MOI number. But if a MOI of .450 is already crazy strong, and the .736 is not really needed, then i may go with the 1.75x.500 wall. The MOI is almost 50% more... jesus, am i rambling now or what?
 

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Union Fab Works
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Discussion Starter #15
Flashover Mfg said:
That's actually not a bad idea. You really need the bending strength (large cross section) at the center of the link, not nearly as much at the end. If you are willing to put in some work, I think a piece of 1.5x.250 at each end attached to a piece of 2.25x.375 for the center would be really strong. I would probably make each the smaller tubes about 15-20% of the overall length of the link and the remaining 60-70% the larger OD. Make sure that the small tube is slid a couple of inches into the large tube so you can get some good rosette welds on it in addition to the fillet weld at the transition point.

Hmmmmm, might be an idea... i get scared tho with the smaller attaching point... but i trust your advice, so i will add it to the list of possibilities.
 

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Another tool that can help in determining your material is in the 4 link calculator. The material section of the calculator will give you a factor of safety in the bending of your links. A F.S. of 1 or greater in the calc means that the link can support half of the weight of the vehicle without the link bending. A F.S. of 2 means that your link is twice as strong as needed to hold the weight of half of the vehicle. It does not, however, account for impact loads such as falling off a ledge and landing on your link.

Ryan
 

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The bending stresses in a bar are greatest at the point of loading (ie a rock inthe middle of your link. The bending stresses decrease to zero in a linear fashion to the end of the link. As bending stresses decrease, shear stresses increase. Bending stress is handled by having a large force of bending allowance, which comes from a large moment of inertia. Shear stress is handled by the actual cross-sectional area of the material in the bar. Your chances of a link failing due to shear stress is very low, as a large material cross sectional area is almost absolutely necessary for a large moment of inertia.

Sorry if this is not very clear. It has been a few years since my last materials engineering course.

Ryan
 

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carwash said:
Yes, the 4 link calculator will be the next enigma i dive into... ugh. What is the link for the latest version... do you have it handy?
No, I don't have a link, but it should be in "triaged"s sig line.
 
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