SCCA says:
Up to 1500 lbs.
1.375” x 0.095” Chrome-moly / Seamless mild steel (DOM)

Okay, great, my car will be lighter than that. The problem is that Autopower (local to me) only handles 1.5" and 1.75" tubing. I could overlook the large size for a small part, but the weight savings (30%!) is too much to ignore for an entire cage. So who bends 1.375” x 0.095” DOM in SoCal? I wonder if the offroad guys use that size.


Modified by kb58 at 2:22 PM 3/25/2008

 

I thought you just needed the correctly sized die?

 

Yeah thats a pretty unusual size, not sure if anyone would use it.

Can you find out what bender they use? Depending on the bender, I'm pretty sure you'll be able to find a die (probably will be about $200) for it.

 

I'm puzzled that it's an SCCA-approved tubing size and no one bends it. I doubt people bend it themselves since I think it needs a mandrel bender.

 

Mandrel bent cages are more the exception than the rule. Mild steel DOM will bend fine on a regular bender.

Sam Rothchild in Riverside does good work and has a nice bender. I'm sure he'd be willing to do it if you pay for the dies.

 

What about Sports Racers? They'd qualify in that weight group, right?

 

I think so. I realize there must be lots of people who can bend the stuff, it's just a matter of finding them. Preferably someone in SoCal.

 

just go 1.5" with .083 wall
that should weigh about the same and be stronger.

 

I was thinking about that, too. I'll have to compare the strengths between the two but it would probably work.

 

KB try John at Revenge Motorsports in Santee. If he can't do it he will know somebody who Can. I am sure he would love to see Kimi in person.

 

Could look up any off road fabrication shops in your area.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kb58 &raquo;</TD></TR><TR><TD CLASS="quote">I was thinking about that, too. I'll have to compare the strengths between the two but it would probably work.</TD></TR></TABLE>

you just need to do area moment of inertia which is a 15 second formula.

Moment of inertia, round tube = (PI/64)*(Do^4 - Di^4)
i dont have any books with me so i just pulled that off the web. looks right though.

 

I talked to Rick at Autopower, about buying a die for their bender. AHAHAHAHAHAHA, says Rick, gently letting me know it's $$$$. Okay, lesson learned there. I'll call them back and ask, since they can bend 1.5 x 0.120, can they also bend 1.5 x 0.083?

As an aside, I know a bit about Rick's background and asked if he'd ever met Burt Monro ("World's Fastest Indian") at the salt flats. He said he did as a kid back in the 1960's. Pretty cool I thought. If you haven't seen the movie, SEE IT. Not too many people pour their own pistons...

And thanks D Rex, I've noted it if the Autopower thing falls through.


Modified by kb58 at 6:52 PM 3/26/2008

 

The 1.5x.083 would be stronger than the smaller tube. But many sports racers use that size tubing.

 

No-go on Autopower. They use mandrel benders which means the smaller mandel would probably allow kinking or tearing of the thinner wall. Guess I'll try John at Revenge. Thanks for the input guys.


Modified by kb58 at 9:15 AM 3/28/2008

 

Been thinking this through a bit more. If going from 1.375 x 0.120 to 1.5 x 0.083 is a good thing, I wondered if I could go to 1.75 x 0.060.

Technically, yes... it's stiffer and lighter, but that's not the sole function of a rollcage. That is, if the car turns over and, say, rolls over a small rock, it'll kink the large OD but thin wall tubing. That'll ruin all the strength in the cage which seems like a really bad thing.

I have to think about this more.

 

i am getting slightly confused because you first cited SCCA rules and now it looks like you are looking at tubing outside of scca rules.

i would not build anything without making sure it complies with scca and nasa rules. look for the common ground in the most likely organizations the car would be. with either you as the owner or if you need to sell it.

and i am not a fan of chrome moly due to stress hardening issues....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tom91ita &raquo;</TD></TR><TR><TD CLASS="quote">and i am not a fan of chrome moly due to stress hardening issues....</TD></TR></TABLE>
X2

The funny car guys leave their chassis unpainted just so they can check for cracks. I'd rather have something painted that's less prone to cracking. Maybe if I had a crew of WD-40 wiping, crack checkers then chrome moly would make more sense...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tom91ita &raquo;</TD></TR><TR><TD CLASS="quote">i am getting slightly confused because you first cited SCCA rules and now it looks like you are looking at tubing outside of scca rules.</TD></TR></TABLE>
I'm building something for trackday events, so technically it doesn't have to meet SCCA rules. However, I'm well aware of how the rules came about, learning the hard way that thinner tubing fails, and having the car fold up isn't the plan.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley &raquo;</TD></TR><TR><TD CLASS="quote">
X2

The funny car guys leave their chassis unpainted just so they can check for cracks. I'd rather have something painted that's less prone to cracking. Maybe if I had a crew of WD-40 wiping, crack checkers then chrome moly would make more sense...</TD></TR></TABLE>
x3. It will not be chrome moly.