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-square-roll-bars/dp/B0006RCLM2/ref=sr_1_1/104-4398766-3291966?ie=UTF8&s=books&qid=1187134520&sr=8-1

[gt1guy]

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

Good idea here. You'd still be able to use a DOM tubing. Square & Rectangular tube is ERW, and that's not what you want.

Kevin

[69stang]

I'm utilizing 2x3 tube inboard of my rockers and 2x2 tube for the A-pillar pieces and B-pillar/main hoop. The square tube fits the factory roof reinforcing rib above the B-pillar. I have access to dense foam padding and will be making a headliner that incorporates the roof bars and will be padded. As the picture shows, I'm also using round tube. The picture shows what I would call the general configuration of my framing and cage. Things are changing as I'm building. For instance, most everything behind the B-pillars will change based on my suspension setup. What's in the picture is just some generic geometry. I've already welded in the rocker rails, A-pillar posts & B-pillar posts on the right and started on the left. I would've liked to run my car on the track from time to time but realize my car probably won't meet any of the sanctioning rules. That's not an issue as I plan on just driving and enjoying the car.

[Damn True]

I'd love to see what you have in mind for the headliner.

[69stang]

I'm thinking a fiberglass headliner with dense foam around roof bar areas and covered in vinyl. The headliner will also have a console area down the center for some switches and I'm thinking a display screen for audio control. I don't want to butcher my dash, I like the factory design. The picture above doesn't show any cross bracing at the top or behind the driver which I plan on installing also.

[KUL FIR CHICK N]

I've seen Art Morrison's bender. He can mandrel bend in either the "easy way" or the "hard way." That means the short or long direction on the rectangle. His bender does beautiful bends. He does custom work; all you need is a drawing of what you want.

Like James said, if you had a 2" square tube and a 2" round tube of equal wall thickness, the square tube would be ~ 1.7 times stiffer. BUT, the square tube has much more steel in it. Weight for weight, the round tube wins. The 2X3 hoop you're proposing, if properly bent, would be much stronger than a standard 1 5/8 hoop, but it would weigh a ton, and you're putting all that weight up high, where you want it least.

[Kenova]

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

This would be my choice. I think it would look more elegant and, although I'm no engineer, I think it would be stronger than a single square or rectangular bar.

Ken

[nancejd]

It would be marginally stronger in the short direction, but have negligable additional strength in the long direction. Resistance to bending is a function of the amount of material as a factor of the distance from the centroid of the shape. That's why wide flange beams are so efficient in floors, and you usually see tube steel used as a building column instead of the wide flange. I wonder if you could use a thinner wall section to regain some of the weight savings of the round tube. Of course, if you're racing this won't apply, since you'd be lucky to get the inspector to accept ssquare vs. round tube to begin with, let alone varying the wall thickness.

[ss dave]

Go to Prodigy's website and look at Pete's Camaro's bar. I believe that is the look you're after. Frank has done this type of roll bar with that look but with round tubing.

[BAILEIGH INC]

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[Jim Nilsen]

All of the cages on the fork lifts at work have rectangular or square tubing and solid flat stock. They are heavier than all get out and hold up as well as round would from what I can see when they wreck them. I have seen some punished forklifts beyond what we can do to our cars.
Square is just way too much more weight for the same size dimension across and harder to work with. I have never seen a cage made of square or rectangular tubing with any bends in them, just cut ,welded ,gussets and fish plates.

[GetMore]

All of the cages on the fork lifts at work have rectangular or square tubing and solid flat stock. They are heavier than all get out and hold up as well as round would from what I can see when they wreck them. I have seen some punished forklifts beyond what we can do to our cars.
Square is just way too much more weight for the same size dimension across and harder to work with. I have never seen a cage made of square or rectangular tubing with any bends in them, just cut ,welded ,gussets and fish plates.
I suspect that a square tube cage is stronger than round tube when used in an application like forklifts and heavy equipment. The tube can't be bent, it must be welded and gusseted to make turns to keep the strength.
In those applications forces are usually applied from the front or side. I think tipping on the side is the most common.

[1360]

There was a funny car from the '60's that ran a square cage.....folded in the first wreck & killed the guy.

To make a square tube cage strong enough (like on industrial equipmnet), it would weigh a ton more than a round tube.

Good luck!

[1969CamaroRS]

It would be interesting to see a square tubing roll cage/bar done so that when finished you could barely tell it was in the car (form fitted to the pillars and roof etc).

[b-man]

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-square-roll-bars/dp/B0006RCLM2/ref=sr_1_1/104-4398766-3291966?ie=UTF8&s=books&qid=1187134520&sr=8-1 The square roll bars 'back in the day' were were usually made from either round exhaust tubing or plumbing pipe. A lot of chassis building was done using both of these materials.

They were square because the corners were welded together at 90-degree angles and not bent in most cases, not because they were fabbed from square tubing, not that there weren't some made from square tubing as well.

This was long before there were really any rules or established practices for this type of safety equipment, it was quite common for the top of many of these early roll bars to be below the height of the driver's head.

Seat belts were optional back then too, a lot of NASCAR drivers even into the '60s didn't use them.

A lot of guys died in crashes that would only slightly injure a driver today using the modern roll bars or cages and restraints.

[newby]

i'm quite sure if you put in the time and engineering you could have just about any cage approved. depending on the sanctioning body, computer analysis might be enough, others would want destructive testing.

never assume that just because something is usually done a certain way that it is the best way. never assume that just because someone else has tried something in the past and failed that you will not succeed.

[Twentyover]

i'm quite sure if you put in the time and engineering you could have just about any cage approved. depending on the sanctioning body, computer analysis might be enough, others would want destructive testing.

never assume that just because something is usually done a certain way that it is the best way. never assume that just because someone else has tried something in the past and failed that you will not succeed.


Perhaps so. The question is, is the time and effort involved in justification of the deviation from norm compensated for by reduced manufacturing costs.

While the way it's done today may not be the best way, it's is a proven way. Just because they failed in the past is no guarantee you will succeed with this effort. Improved fabrication technology is no guarantee of sucess. You need to understand why the prior effort failed, and design around that feature. Even then, even if you mitigate the prior failure, there may be other failure causes. You will probably end up pushing a rope with regard to the sanctioning bodies.

[Bryce]

i guess i am still confused on why u want to use square?

A roll bar is just that, a bar to protect you if u roll the car. Round DOM tubing has been tested over and over. as previoulsy stated square wall is not regulary found as DOM (drawn over mandrel) and is typically welded therefore weaker.

[funcars]

Take a look at the yield strength of DOM used in typical rollbar steel tubing vs ERW in rectangular tubing. Then think about the extra weight needed and where that extra sits relative to the cg of the car. Kind of answers itself. Also, the closer you are to accepted practice the more likely it is that tech inspectors would let you run at a track.