[mitchntx]

IN an effort to lose weight off the race car, I want to cut the SFCs off. However, I use them to jack up the car.

After seeing several "pro" teams use a receiver/stab setup off the roll cage, I began fabricating this kind of rig.

I used 1" square tubing as the receiver and gusseted the hell out of it to keep deflection to a minimum. I have some 3/4" solid bar stock I was using as the stab.

After welding the receiver portion to the cage and mocking up the stab with plenty of gussets, I tested the rig and ... it bent. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/mad.gif) 3/4" solid bar stock bent like a pretzel.

And it yielded right at the end of the gusseting. Think of it as a pry bar.

I opened the door and placed the jack on the end of the receiver and lifted the car without an issue ...

So help me out here ... what can I do to the bar stock I have to increase it's strength or what kind of 3/4" bar stock can I source that will lift 1500lbs?

[mitchntx]

The stab ...

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab.jpg)



The stab fully inserted.

(IMG:http://www.lawmotorsports.net/Pics/Mitch/stab_receiver1.jpg)

After closer inspection, it appears the end of the receiver is deformed as well, just beyond the gusset on top.

Again, the stab was a mock up in order to find the weakness. I didn't spend a lot of time on it.

I added in about 10* off vertical because I realized that as the car goes up, the angle change would add leverage.

Maybe I didn't add enough angle?

Maybe I under built the whole rig?

[StanIROCZ]

I assumed a 6" lever arm and 1600 lbs of load and came up with 364 ksi stress. Regular off the shelf mild steel is good for ~50. I don't know of any steel that can handle 364 ksi.

If you take the gussets out completely you can slide that 3/4 stock in farther to reduce the 6" lever arm that I mentioned above. If you can get the vertical bar within .5" (zero would be better) of the end of the square receiver your stress goes down to 30.3 KSI. To do that your verticle tube will be almost touching the rocker panel.

But really, you should have the gussets because your failure mode will probably shift to the weld (or atleast it would scare me).

Maybe I under built the whole rig?

Yeah, I think so. I would probably use 2" next time and you wouldn't need a solid bar stock. A .250 wall will be pleanty. And keep the lever arm to a minimum.

[StanIROCZ]

I assumed a 6" lever arm and 1600 lbs of load and came up with 364 ksi stress. Regular off the shelf mild steel is good for ~50. I don't know of any steel that can handle 364 ksi.

If you take the gussets out completely you can slide that 3/4 stock in farther to reduce the 6" lever arm that I mentioned above. If you can get the vertical bar within .5" (zero would be better) of the end of the square receiver your stress goes down to 30.3 KSI. To do that your verticle tube will be almost touching the rocker panel.

But really, you should have the gussets because your failure mode will probably shift to the weld (or atleast it would scare me).

Maybe I under built the whole rig?

Yeah, I think so. I would probably use 2" next time and you wouldn't need a solid bar stock. A .250 wall will be pleanty. And keep the lever arm to a minimum.

I have a better idea for your design that will reduce the amount of mass on the car and increase the strength. If I get time tonight I'll sketch it up and post.