square tubing cage

[ks-sparky]

who makes or can make a hoop made of 2x4 to 2x6 tubing it doesnt have to be those exact measurements. for a first gen camaro.
thanks for any help

[71dusterdan]

why? a rectangular or square tube does not bend like a round one. it will crush on the inner radius, which is considered wall fatigue and it will just fold up if it ever needs to save your life. cutting and welding is better but still not equal to a properly bent round tube. then you have to factor in protecting yourself from the corners of the tube. there is readily available padding for round tube, designed and certified for the purpose, try and pad flat surfaces on a sq. or rect. you will be on your own there. then there is the aesthetic point, it is straight with sharp edges, in sq, or rect. it will look out of place in a car with a lack of geometric shapes. sorry , i'm not trying to shoot you down but from a safety standpoint it just isnt. many companies will sell you a basic hoop cheap, and you can have one bent custom by an infinite number of companies with a little legwork. i have seen show cars with oval bars for hoops, cant weigh in on the safety, it is usually two bars bent identical and then filled with sheet metal, or a carefully cut round tube that is then ovaled with the addition of sheet metal strips. again sorry i didnt mean to break you down or hurt your feelings, but your idea could just leave you DEAD! Dan

[70TWO NOVA]

Theres a reason you dont see them.

[ks-sparky]

i do alot of offroad rockcrawling and i saw one at a event and really like the way it looked. the guy who had it worked for ditchwitch and had it done there. honestly i figured if you had some triangulation tied in with the cage it would be fine. i have never had a high speed roll over but i have had a few mild rollovers so i do understand and want it to be safe. thank you for the reply and opinions

[jason@gmachine]

please dont, its just not safe.

Jason

[wick]

Exhaust pipe might be stronger and lighter. LOL

[ks-sparky]

wick thanks for the advice, im shure it makes you feel good to help others not as wise as your self.

[70TWO NOVA]

Hey, asking questions is how you learn! Its when you dont that you end up looking real stupid.

[nancejd]

Honestly, I don't see why it couldn't be done. Rectangular tubing is used for frame rails all the time, and I suspect that that takes quite a bit of loading without failing. I think the key would be to have it mandrel bent so that the walls of the tube didn't crush. A round tube thins just like a rectangular tube does when bent with a mandrel, that's why the bent peices usually use a wall thickness that is thicker than the minimum, so it doesn't fail at the bent parts. A couple of things to keep in mind though, finding padding would definately be a challenge, and it would weigh more than a round tube bar would for an equivalent amount of strength.

[MrQuick]

Sparky, is this for rock crawling or anything over 18 mph?

[paul67]

I would think if you looked at some tech web sites for tubing and box section spec's you would see how week the box section would be compered to the tubing.

[71dusterdan]

well in answer to the comment about mandrel bending sq, and rect tube. now i am no expert, and there may be benders that i have not seen, but the benders i deliver steel to everyday all crush the inside wall. the inner wall fails and rounds to the inside of the bend, meaning it protudes into the interior of the tube. now i dont know how art morrison handles this with his max g chassis. maybe there is some other kind of bender. flipside, dse, hydroforms there front subframes, most likely because the inner wall of the tube does fail. so i would say the most common benders, including mandrel, will compromise your tube strength. so i still vote for the passing on this idea, sorry. Dan

[nancejd]

A bender will make the tube thin on the outside of the bending radius, and bunch the material together on the inside, whether the tubing is round or rectangular. From what I understand, one of the advantages of a hyrdro formed rail is that the material thickness remains uniform in thickness. Since the material thickness is more unifrom, you can use an overall thinner wall, and get the same design strength. With a mandrel bender, you can only calculate design strength using the thickness of the material as it is thinned in the bend. That's why roll cages in general use a wall thickness greater than the sanctioning body requires, to allow for material thinning in the bending process.

Given identical materials, the ability to resist bending is a function of material area and the square of the distance from the centroid of the shape (why an I-beam works better in one direction than another). So as you can see, this also has to do with the direction a shape is being bent in. Given that, if you had a square and round tube of identical wall thickness, and identical width (measuring perpendicular to the surface of the tubing), the square tubing will resist more moment. It would resist even more moment if you could get it to bend diagonally (which of course you can't, since it would buckle in the weak axis).

I suspect that the real reason square tubing cages are uncommon is that it would be a fabrication nightmare. With a round tube, you have a single plane cut at the end of a tube, which has to be fishmouthed. Imagine trying to get three or four square bars all come together in a nice joint.

I'll admit, I'm not an engineer, only an architect, so most of this stuff applies to building structures (and I haven't done any steel calcs since I was in school), but I would assume that building steel operates the same way as car steel.

[ks-sparky]

noi this was not for rock crawling but my point was if it can take that kind of abuse, why couldnt be used in my car. my idea was that if its strong enuff for ditch witch it should work for my ride. someone did make a good point on the weight and roll bar padding both being issues. i was thinking of the use more for visual like then saftey use, one way or another i will need a cage. thank you for your input.

[CamaroAJ]

easy test.....take a piece of copy paper and fold it 3 times and tape the ends together so you have a square, roll up another piece so you have a tube. put a regular red brick on it and see what one will hold the weight.

[MrQuick]

In that case the only safe and strong way a roll cage built of straight rectangular pieces would be a geodesic design and that would require alot of metal. Even then it might not be as strong as a tubular type.

Even though a frame is make of square tubing,it is srong for its application. This would not be a fair comparison because it goes through a different stress than a roll cage would have to endure. Crushing as opposed to twisting.

[nancejd]

I'm not sure the paper folding vs. rolling is a good example, since the wall thickness wouldn't be the same. Now, if you cut the paper so that it was an equivalent diameter to the and a single layer of paper thick to the square, then that would be an equivalent test. The seam might be the limiting factor, but as long as it was equivalent, I'm not sure it would matter for the experiment.

Strictly speaking, I don't think that a cage crushes. Material crushing occurs along the longitudinal axis of a shape. When a cage takes an impact, it would be expereinceing a sudden point load along it's length, causing it to bend, and possiblly deform permamnently if the loading exceeds the yield stress. Basically, for a cage to crush it would have to get shorter.

I think the bracing would look essentially the same as a round bar cage, but it would certainly be more difficult to fabricate.

Any materials or mechanical engineers out there that would like to comment? I'd love to hear any more technical information on this.

In the end though, I'd be less concerned about the appearance of the cage than the safety of it, and since finding padding would be an issue, I probably wouldn't do it. One advantage it might have would be if you were trying to get the main hoop up above the headliner, but I don't think any sanctioning body would allow that, so it wouldn't be a competition legal cage then.

[Damn True]

The ACO, FIA, SCCA, NHRA and NASCAR have put a lot of time, money and effort into establishing what is and what is not a safe cage material and cage design. If square tube had any benefit it would be in use. It isn't in use. From that we can safely deduce that it isn't safe.

[Steve Chryssos]

If you will not be racing, then build a double rail round tube structure and face it with sheetmetal. There.

[68sixspeed]

There is a book out about drag race cars from the 50's and 60's titled "Cool Cars, Square Roll Bars"- (I know one person/car in it, but he did not run square bars.) I've heard of square roll bars 'back in the day'; anyone find a copy of this book? I'm sure weight for weight round tube is the only safe way to go, but it might be a stretch to say square tubing is unsafe. Just not as practical.

http://www.amazon.com/Cool-cars-squa...7134520&sr=8-1