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Discussion Starter · #1 ·
I'm going to be fabricating some things at the machine shop here on campus soon. First thing I'm going to make is a set of toe links, I'm using the SPC ones as a model. What kind of metal should I be using for this, and where can I get some quality Heim joints? I'll also be making some sway bar end links for the rear.
 

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Figure out the stresses that will be applied to it (more then stock obviously, maximum rated load) then times it by 8, you should have a KSI or MPa final, and pick a suitable metal from there. That's what the real companies do.

You could just non destructive test the one you have now to find what kind of material and grade it is, and use the same material too ;) .
 

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Hmmm, i would use 17-4 stainless (expensive, hard to machine, but very very strong and corrosion resisant), or 7075 aluminum (also expensive but much stronger than 6061). but to know for sure you should calculate the theoretical loading characteristics, determine the stresses in the principle directions, etc. multiply by a safety factor and then compare to different materials.
 

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Discussion Starter · #4 ·
jmart said:
. but to know for sure you should calculate the theoretical loading characteristics, determine the stresses in the principle directions, etc. multiply by a safety factor and then compare to different materials.
OR... put them on someone else's car and drive it hard for a few hours!
 

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I looked at the two designs that SPC has. The one I'd replicate would be part number 69460 as it is much simpler, and I just like it better. All you need are a couple heim joints. Search for "heim joint" at mcmaster.com. You can specify material and size and they have them in various strengths. Then also order some metal stock from them: a round bar or tube with sizes corresponding to your heim joints. Then all you need to do it use a lathe to drill and tap the inside diameter of the metal stock. Add a couple lock nuts and bam, done and done.
 

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Also, you could put the finished product in an instron at school and test to failure....
 

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Actually, now that I think about it, if I were you i'd buy the heim joints of proper size in a medium strength. Then look around the machine shop for a piece of 6061 aluminum stock that will work for you, and I'd tap it, assemble it and put it on. Or see what your shop has in medium strength steels that are still machinable.
 

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With something that small, make it out of 4130 steel. You might as well, it'll be cheaper than Stainless. The 7075 Aluminum that was previously mentioned would work too. I wouldn't use a material any weaker than that, just in case.
 

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Discussion Starter · #11 ·
jmart said:
Actually, now that I think about it, if I were you i'd buy the heim joints of proper size in a medium strength. Then look around the machine shop for a piece of 6061 aluminum stock that will work for you, and I'd tap it, assemble it and put it on. Or see what your shop has in medium strength steels that are still machinable.
Would that be strong enough? There's plenty of that lying around... for free too!
 

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I dunno, let me think about the stresses that that link would see.

I do have another Idea though. You could reverse engineer the link by lookign at the geometry of the old piece and seeing what kind of max forces and moments it could handle before failing. Then see if a link emade with 2 hiems and some 6061 would work. Basically the hiem joints will be pleenty strong. They are made form hardened steel and have a geometry that makes them hard to break. The real question is will the threads of the aluminum piece hold when the piece is in tension. You figure there really are no moments about any of the principle axis at either mounting point as a result of the hiem joints. Fo rsimilar reasons you've got no shear forces in any radial direction, only in the axial direction. That means tension and compression only. Compression is less of an issue becasue the steel threads of the hiemst ake the loading from thelock nuts, who take it from the face of the aluminum tube. And that tube isn't goign to fail in compression at the loads we are talking about. But in tension I would worry about those aluminum threads. You can find one of your mech-e buddies as school and have him calculate the number of threads needed for a certain base circle diameter and thread pitch and thread cut angle and the material properties for a given input load.
or you could just sya fuck it and machine the center piece of 6061 and giv eit as many threads as possible. If you do so rememner that finer threads ar ebetter than coarse threads, for a couple of reasons.
Anyway, I've beend rinking and I think i've been rambling, most likely about nothing much.
 

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Hmmmm, okay, now that I think about it, that little linkage doesn't take very much loading at all. The main load pat seems to me to be through the big bushing in the trailing arm. Then lesser load paths would be through the bushings on the toe link. however, by replacing the semi-rigid bushings with hiem joints hich pivot freely, you will actually be eliminating the toe link as a torsional load path. This will ultimately make the trailign arm bushing take more of the load, to a point. I say make the links out of 6061, but also make sure that you've got some nice stiff trailing arm bushings, or at least new ones if they are just oem type.
 

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Discussion Starter · #14 ·
Wow jmart!

I'm not actually an engineer, physicists usually just pay engineers to research this stuff...

I'm going to talk to one of my friends who's in an automotive engineering class now, I've read a little of his book, and it's interesting (where I can understand it). He also took a class in metallurgy last semester.
 

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downest said:
I'm not actually an engineer, physicists usually just pay engineers to research this stuff...
Actually, I think its the other way around my friend... :rolleyes1:
 
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