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Ok so this is the results I have using 1.375x.095 round tube for the cage and .75x.75x.125 for the rest of the frame. This time I constrained the frame at the shock mounting points as suggested by blackbird. The results are closer to what I want and my whole frame only weighs 177 lbs. I applied an equal an opposite force on the front and then the rear. The result for the front is 3168 ft*lbs/deg and the rear is lower at 2066 ft*lbs/deg so I may add a tube or change a few to larger tubes at the rear.

? anyone ever used .75 square tubing for the whole frame plus cage?

blackbird there are two sections that conflict eachother
11.4.7 on page 43 of the NASA rule book gives the following

Vehicle weight DOM or ERW
Under 2000 lbs. 1.50" x .120”
2001 - 3500 lbs. 1.75" x .120"
Over 3500 lbs. 2.00" x .120"

Vehicle weight Alloy (CM)
Under 1500 lbs. 1.375" x .095”
1501 - 2500 lbs. 1.625" x .095"
Over 2500 lbs. 2.000" x .095"

while in section 15.6.18 page 62 is states what you have said

Up to 1500 lbs.
1.375” x 0.095” Chrome-moly / Seamless mild steel (DOM)
1501 - 2500 lbs.
1.500” x 0.095” Chrome-moly / Seamless mild steel (DOM)
1.500” x 0.120” ERW* (No issuance of log books for cars with ERW cages 04/30/03)
*Note- Specifications listed for reference for inspection of grandfathered vehicles.
2501 - 3000 lbs.
1.500” x 0.120” Chrome-moly / Seamless mild steel (DOM)
1.750” x 0.095” Chrome-moly / Seamless mild steel (DOM)
1.750” x 0.120” ERW* (No issuance of log books for cars with ERW cages 04/30/03)
*Note- Specifications listed for reference for inspection of grandfathered vehicles.
3001 - 4000 lbs.
1.750” x .120” Chrome-moly / Seamless mild steel (DOM)
No ERW allowed.
Over 4000 lbs.
2.000” x 0.120” Chrome-moly/Seamless mild steel (DOM)
No ERW allowed

I plan on using DOM so there is a conflict

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ok, i've been working on this for a while and i hope it helps someone. i've inclosed pics for the new data for a primarly 1x1 1/16 gauge square tubing with 1.375x.095 round tubing. i did it with and without the engine which is hard mounted (or will be). hope this helps with that discussion. but anyway here ya go

.75” 1/16 square tubing with 1.375x.095 round
Front=3168 ft*lbs/deg
Rear=2066 ft*lbs/deg
1” 1/16 square tubing with 1.375x.095 round
Front= 5165 ft*lbs/deg
Rear=2940 ft*lbs/deg
1” 1/16 square tubing with 1.375x.095 round with engine removed

Front= 1352 ft*lbs/deg
Rear= 1516 ft*lbs/deg

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Section 11.4 refers to roll BARS while section 15.6 refers to roll CAGES.
Big difference .

I went with 1.5 tubes for my cage knowing what kind of cars I'll have next to me on track, most of which weigh at least double.
I'd go 1.375 if I raced other sevens or similar sized cars.

Moti

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Oh!! I didn't realise the different notation. I will most likely go with the smaller since there will be more tubing outwards when I figure out the body.

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Can someone do me a favour? I'd like to see if the roll car on our car can support it if it ever flips. I know this is stupid but It may be sometime before I cage the car. It's a standard 442 frame with a single roll hoop. The hoop is 2'' dia I'm not sure the wall thickness but let's say whatever the average wall would be for a 2'' pipe. Here's a pic of what it looks like.
http://www.deman-motorsport.com/photos/image32.jpg You don't even have to make a new frame just use an existing one that is about 140lbs or so. The total vehicle weight will be 1200lbs. I'd really appreciate it as I can't figure out how to use an FEA program.

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Deman Sr7 build turning laps once in a while

Sorry to be the party pooper, but that "roll bar" is crap.
You'd be better just making a proper roll bar which is really not that hard or complicated.

Moti

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Personally, I would never even consider 3/4 x 3/4 x 0.125 tube. To improve stiffness, increasing the diameter is MUCH more effective than increasing the wall thickness.
3/4 x 3/4 x 0.125 tube is approximately 30% heavier than 1x1x0.065 (the locost standard 16g tube), AND its only 60% as stiff.
Going the other direction 1 1/4" square 18g gauge tube (0.049) is 60% stiffer and slightly lighter than 1x1x0.065.

I think that 1x1x0.65 is a good compromise here, I'd be scared of cracking my frame with 0.49 tubing.
If you really wanted you could switch just some key tubes to 1.25x1.25x0.65 and add a little bit of weight but make the frame stiffer.

Moti

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FWIW, I found 1.375" tubing very hard to find, let alone anyone with bending dies for it. I went with 1.5" x 0.095.

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The bar shown on that car is a "style bar". I wouldn't use a 4, 5 or 6-point belt in that car. If that car goes upside down the bar may fold to the horizontal postion (fore or aft), you'll want to lay down to try to save your head/neck. Use a 3-point belt if you have one of those bars.

well i just put in a material order!!!! this is what i got

120' of 1x1 16 gauge
80' of .75x.75 16 gauge
~100' of 1.375 DOM tubing with .120 wall thickness
24x24 11 gauge plate for mounting points
48*48 16 gauge plate for passenger area.

later I'll most likely get some aluminum and cover the whole bottom.

as far as

I di the calc with .75x.75 16 gauge and got decent results. i went with what i did because this setup is only ~200 lb without plating. plus my analysis was not including any flat plates so it will end up stiffer

thanx for the help guys. i'll be updating my build long one i actually get some build done next week!!!

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well ya'll saved me alot of headach's. i just changed the order from 1.375 to 1.5OD. it seams that not many places have that die. so should a muffler shop be able to bend 1.5 with a wall thickness of .095?

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Muffler shops don't do mandrel bends normally.
You'll need a shop that does mandrel bending for your cage to be race legal, crush bending that muffler shops do does not qualify.

Moti

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This is a common misconception. Roll cages are not mandrel bent, as mandrel bending means putting a mandrel INSIDE the tube. The cost of that is usually too high, and as this link explains may make the tube weaker. Mandrel bending stretches the outside of the tube more than a regular unsupported bender, making the wall too thin.

The reason exhaust tubing crushes so much is because of the relatively thin walls. I was just at my buddies exhaust shop, and the tool they use for exhaust tubing is identical in design to the tubing benders used for making cages. The only difference is that his was hydraulic and had dies up to 3" in diameter. If you take some tubing to an exhaust shop with one of these, I bet the bend ends up being just as good as a JD2 type bender used in a lot of race shops. I would ask them what the centerline radius is though, to be sure it's not too small.

http://www.vansantent.com/definitions.htm

Ken

Whilliam's LowBuck Tools sells a bender with that size die, 1.375". Also a good tubing notcher.
http://www.lowbucktools.com

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