tubular lower control arms for coilovers

I just started reading this thread....very interesting and very good fabrication, as I have been thinking about modified A body front suspension work. I almost hate to bring this up, but I can't look at this and not do some analysis on something that jumped right out as a possible issue. (I sincerely apologize to the OP for saying this after so much hard work.)

The issue raised earlier in the thread about the stress in the threaded portion of the rod end sticking out of the end of the LCA is very real. Some straightforward calculations, with a typical car weight just sitting still and assuming 3/4" fine threads on the rod end, shows the stress on the lower edge of the threads where it enters the threaded bushing to be around 50,000 psi. Yield strength of 4130 steel is in the range of 66,000 psi.

So it looks like it will not take much impact loading (think: small pothole) to bend the threaded portion of the rod end. And yeah, I realize not all calculations are the end-all and be-all, but this is so close (in just a static setting) to the yield strength of a strong steel that it looks to have very little margin. And the earlier info about the rod end strength of 15000 is likely for radial strength; that has no bearing on how this part is being applied.

Bottom line: Rod end are not designed to be used with cantilevered loads on the threads, which is inherent in the design here. I see the inner pivots of some wishbone LCA's using rod ends in a similar way, but the mitigating factors in those are that these use 2 rods end to split the load, and the force acting on them is a fraction of the load in this type of set-up.

You can read here to see more on this and duplicate the computations:
[ame]http://www.aurorabearing.com/pdf/rod-ends.pdf[/ame]
and here:
[ame]http://americansolarchallenge.org/ASC/wp-content/uploads/2013/01/rod_end_calculations.pdf[/ame]

For reference on another aftermarket LCA design, look at the HDK tubular LCA's and see how the material between the ball joint mount and the end of the tube and coil-over is short and stout. The short distance lowers the bending moment considerably, and that, plus the increase in thickness, makes the internal stress around 20-30 times lower than in the design shown in this thread.