Threaded load AL6061 and rod end

[rcrescencio]

I need some guidance on determining the minimum thread engagement needed between an aluminum (6061) female stock and a 3/4-16 rod end (steel-chromoly).

Thanks,

RC

 

[BUGGAR]

I generally design to standards of the Aluminum Association but they don't seem to cover thread strength. They cover allowable loads on tension/compression members if that's what you need.

I do off road stuff and usually resort to testing these things. Not hard to rig up a loading mechanism.

 

[hydtools]

I've used a thread engagement of 1.5 diameters. With 6061 you may want to consider using a thread insert like Helicoil. You did not say, bit I assumed your using 6061-T6 or similar.

Ted

 

[rb1957]

how much load are you applying ? If you thread directly into the Al there could be issues corrosion (Al and Steel). Heli-coil would be a good route.

another day in paradise, or is paradise one day closer ?

 

[BUGGAR]

I'm leaning on the Heli coil as well. They publish useful strength values. Heli coils are good for assembly and disassembly in aluminum as well, although I don't think that is your problem. Of course, you'll have to cut deeper threads in your control arm thing for a heli coil.

 

[desertfox]

Hi

As others have said a helicoil insert is probably the best way to go, however for a material with equal strength of the bolt grade you are using I would recommend a thread engagement of one bolt diameter as a minimum.
You really need to establish what external load the joint will see in service and with that information you can determine bolt size, insert etc.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[rcrescencio]

1. Doing the destructive scenario is not practical, nevermind expensive.
2. I don't know the loads, although i could get some approximations. This is for a front control arms on a 3100# race car (weight distribution is close to 50/50). I don't normally pull anything greater than 2Gs (I have done 1.5G sustained).
3. Helicoil would require new (smaller dia.) rod ends, or tapping the aluminum arm to account for helicoil, which means, less material on the arm itself, or a full redesign (not my design - so impractical as well).

The current system is out on the market (by the company who sells them), I'm just trying to determine the minimum required thread engagement, not trying to change the design (rod diameter or aluminum arm).

With the current rod end, I could get the desired arm length, but that would leave me with only 0.75" of thread engagement. If I were to go by the rule of thumb of 1.5x dia, then I'd need 1.125" of thread engagement and there lies my prob. The current rod end is not long enough. I just want to know the actual number vs approximating by a rule of thumb. OR just simply buy a longer rod end.

 

[desertfox]

See this thread404-39629

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[BUGGAR]

I would get the longer rod end. You can never have too much adjustment. Of course, the upper arms will see a lot less load than the lowers and if you have to, use them up there.