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T-top style roll cage?

Old 02-25-07, 03:39 PM
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T-top style roll cage?

Hey guys,

im getting ready to make a roll cage for my TII, and I'm trying to think of a design that will keep it safe without a helmet. I street drive this car quite a bit, so it has to still be safe, but on the other hand, I want to track it, and with the 20B and my driving style, it needs a cage anyway.

What I'm thinking about doing is a standard main hoop ( a little bit farther back than normal maybe) and front hoop, but instead of door hoops I want to connect them with 2 bars about 6" apart right in the middle of the roof. Thats the only way I can think of to keep the cage far enough away from my head that it wont knock me out when I hit a speedbump. Can anyone think of any reasons why I shouldnt do that?

for the rest of the cage I figure I will have removable door bars at about window level that I can put in when I race, and an x-brace in the back.

thanks
Pat
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Old 02-25-07, 04:03 PM
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First thing to think about is where the loads will go if the cage gets, um, 'tested'. The hardest hit when a sedan goes paint side down is usually at the top corner of the windshield . So without some support to send that hit to some other structure you won't get much help from the front part of the cage.

I have sliced the roof reinforcement above the door window to move the cage away from the driver. That will get you about 1" at the most. You can also move the seat toward the center or tilt it a little in at the top. The tilt, if done slightly, isn't a big deal but you can gain a couple inches there as well. Or can you lower the seat? That would be a good reason to buy a racing seat.
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Old 02-25-07, 04:32 PM
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hmm....thats a worrisome thought.

i will be buying racing seats, but they will have to be one of the streetable ones, so im not sure how much lower it will make me. I dont think I could bring myself to cut the support structure above the door, as Im afraid I would end up with less total integrity. Im not sure about tilting the seat either, as im afraid that while it might keep me out of the bar during normal driving, it wouldnt help much if i hit something and get bounced around...I might end up having to do that and just pad the **** out of it, but im trying to avoid it. I guess what I need to do is draw the structure up in ProE and run some simulations on it. Kinda hard to estimate dynamic loads tho, especially with a 2500lb car and a speed that could be anywhere from 2 to 200.... perhaps if i just make a really beefy front hoop tho it might take it. even if it folds the corner in, as long as the braces keep the hoop from folding backwards I might still be ok.

Im a pretty careful street driver (fast, but still careful), so i figure the two scenarios im trying to design for are either a race course rollover at high speed, or some moron in a suv nailing me at a light or something. the race one is easy if thats all i did, but its really the SUV im worried about, since in that situation I wont be wearing a helmet, and may have someone else in the car.
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Old 02-25-07, 05:12 PM
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Since it seems that you don't have to comply with any race regulations then you can gusset the cage to the roof where the reinforcement is cut out, getting it further away and increasing strength.
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Old 02-25-07, 05:32 PM
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do a search....there is over 100 pictures of cages on this thread, think it is "show me pics of your cages."
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Old 02-25-07, 05:35 PM
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well i do need to comply with NHRA and SCCA regulations, since tho i wont be participating in any series, I will be doing single events sanctioned by one or the other....
I looked up some of the regulations tho, and from what i remember they werent very specific as far as design as long as you use the right size material and good quality welds...
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Old 02-25-07, 06:36 PM
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well ****, looks like NHRA requires you to have a standard cage based on their diagram, so unless I want to restict myself to IHRA tracks, I'll have to just cut the roof bracing and try to get it as close in as possible.
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Old 02-25-07, 07:12 PM
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SCCA is also very specific. For the most strength keep it far away from the A- pilar like Black91n/a says and bridge the area with gussets then stuff it up against the roof on the drivers side.
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Old 02-25-07, 07:42 PM
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you guys got any idea of the cost of enough DOM to get this done? Also bends have to be mandrel bent, right? I can do all the welding, but I'm not sure how much its gonna cost me for the tubing and bending? I can probably get the DOM at cost from my buddy's fab shop if need be...

thanks
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Old 02-25-07, 08:55 PM
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Depending on how big a steel order your friend gets figure on about $5 a foot. A full cage in an FC will take around 60-70 ft. Just get three lengths, they come in what is called 20' randoms. Each piece will be 20-24' long.

Bends don't need to be madrel, just not muffler machine bends. You have to keep the bends in a larger radius than 3 times the dia of the tube. Usually cages are bent at around a 6" radius.
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Old 02-25-07, 09:09 PM
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what do you use to bend them then? its not acceptable to just heat and bend them is it?

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Old 02-25-07, 09:20 PM
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I use a tube bender just for doing cage type bending. I suppose a conduit bender for big electrical work would do the job just make sure the bends don't buckle on the inside of the bends. Don't try to heat it, it will just deform.

Doing a cage isn't something you can just jump into and expect to be good. I had a friend that was an engineer at the Mazda plant in Flatrock, Mi. that I let borrow my bender to do a cage. He ended up ruining three lengths of tubing just trying to get his drivers hoop. bent. Thats back when tubing was $2.30/ft, still an expensive lesson.
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Old 02-25-07, 09:25 PM
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haha, i dont expect it to be good, but i figure i can make it fit and pass inspection. Ive done a lot of fab work, just not used to having restrictions on how i do it... the biggest problem will be that I'll have to do all the bending without the car there....i figure i'll get some 3/16" wire stock and make templates with that. i'll go talk to them tomorrow and see what kinda bender he has stashed away in the shop there.

thanks for all the help

pat

Last edited by patman; 02-25-07 at 09:37 PM.
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Old 02-25-07, 09:48 PM
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think i might be able to get away with one of these crappy benders?


pat
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Old 02-25-07, 10:00 PM
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Originally Posted by patman
think i might be able to get away with one of these crappy benders?


pat
Absolutely definitely not. That is a pipe bender and is made for thick wall pipe. You need a tubing bender, made for tubing. Check out williams lowbuck tool for an inexpensive bender.
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Old 02-25-07, 10:27 PM
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oic, wrong size dies. nice how they list it as a tubing and pipe bender, i didnt even think about the difference. unfortunately the lowbuck tool one isnt gonna work out for me. I'll probably use it for this project and like 2 more in the next 10 years, for 500 extra bucks i could pay someone else to do the whole cage. maybe i can find a shop that will let me use theirs.
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Old 02-26-07, 09:53 AM
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Originally Posted by patman
maybe i can find a shop that will let me use theirs.
Good luck with that

Most shops will bend you whatever you need if you bring them some dimensions. It'll cost anywhere from 15-30 per bend.
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Old 02-26-07, 07:03 PM
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I sure agree that a roof halo is tough on your head without a helmet, you could pad the xxxx out of it or you might consider a fixed rear hoop and a removable (bolt in) front section, you can weld in front mounting plates (with nuts welded to the back) for real strong mounting points. There are specific approved ways to attach the bolt in portion to the welded in hoop.
BTW, might set your door bars (SCCA 2 per side req) at/near bumper/impact height.
chuck
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Old 02-26-07, 08:11 PM
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well...im not going to do the bolt in thing. It sounds nice, but i want rollover protection on the street too. I was sorta planning on putting a door cage down low so its easy to get in and out, and then have a removable one at the required 'between shoulder and elbow level'

I'm looking at racing seats, but its hard to tell all the dimensions online. I think maybe i will take a trip to the summit store or something and find a really thin one that sets me down low enough to keep my head out of the bar.

I think ive basically got the design figure out, now I just need to find a local place to do all the bending if my buddy doesnt have a suitable machine at his shop i didnt get a chance to go there today.

What portion of the welding do you guys usually do inside vs outside of the car?

thanks for all the replies,

Pat
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Old 02-26-07, 08:36 PM
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I usually weld most stuff into the drivers hoop before installation. After that I work front to back on the main parts then door bars last.

I have a chassis here if you want me to bend stuff up for you. PM me. If you wan to take a road trip to sunny Florida you can save shipping!
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Old 02-26-07, 11:24 PM
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Along with bending tubes, the ends have to be notched to make a radiused fit to the side of the adjoining tube. If you are going to use 1.5" tubing for the cage, buy a few 10' lengths of electrical conduit at home depot to practice with and make templates. It's a lot cheaper to screw up at $1/ft. than it is at $5/ft. The conduit is schedule 40, so it's marked as 1.75"? I might have that oe wrong, but it's a 1.5" OD. Also, for the safest cage build, don't weld or bolt things to the floor pan unless you have a very large plate there. The best thing is to terminae to the rockers or other boxed in section of the car also using 1/8" plate. Good luck.

-Aaron
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