I'm looking for a metal working project for my highschool mechanics class, and building a roll bar would be perfect. We have already learned how to weld, use pipe benders, and lots of other things I could already do, but now we can put them to use on whatever we want. My question is, what size tubing should I use for a roll bar? I was thinking of 2 1/4" Diameter, and somewhere between 1/8" and 1/4" wall thickness. Anyone know what size would be best?

Also, if anyone has any pictures of how/where their roll bar attaches to on their FB that would help out a lot. I know I need to cut out metal plates, bolt/weld them to the car, and weld the tube to the metal, but I don't know where the best place to attach the bar to the car is.


I'll also be building front and rear strut tower bars, and maybe a front sway bar, but the roll bar is the first project.

 

I may be wrong, but I think thats pretty huge for a roll bar. 1 3/4" at .120 wall thickness is more typical I think. Somebody on this forum must have some rulebooks on hand. What do sanctioning bodies require? (FIA/SCCA?)

 

Coldy, I can email you pics of my cage if itll help. 1 1/2" is appropriate d00d. You dont need that huge tubing. And IIRC, my wall thickness is .095"

 

Carl, I could also use some pictures of this.

 

Yeah, pictures of the mounting points would be very helpful. You can e-mail them to me coldy13@dr.com, and then if you want I can host them for you and put them up here. I guess I'll use 2" tube with 1/8"(.125) wall thickness. I'm not sure what size dyes we have for the bender, but I know we have one for 2".

 

If you are doing this for a class have the kids get an NHRA handbook and the specs from there.
This teaches them how to find requirements as well as do the job.
FYI a roll cage is not as easy a project as a lot of people think to do it correctly. The pipe fitting skills needed where many of the joints connect require a tight tolerance at both ends.
There is no splicing pipes when you make mistakes. Inexperience equals scrap Cutting pieces too short or a little off angle is the learning curve.

If you can get a local commercial plumbing or fire sprinkler company to donate some drops you can have the kids practice by fitting up sawhorses, stools and other projects where you can design some pipe fitting into it to help work them closer to being ready to tackle a rollcage.
You also have to teach them how to weld out of position as well. Have them weld out their entire sawhorse or whatever practice work in overhead position.
you better have some leather ponchos for that

 

Scalliwag, I'm 17. I'm in the class, not teaching it I have at least a month before I will start making this, which is why I wanted to start learning exactly what I need to do to make it right.

The teacher has helped build a couple other roll bars, one for a Jeep, and another for some car I can't remember. He doesn't know anything about cage building, just about the cutting, welding, and putting the pieces together.

 

Well that's a little different then You still need to work with drop and get good at pipe fitting
Roll bars in trucks and roll cages are very different. Truck roll bars are easy compared to roll cages.
Pretty much all the suggestions I gave are still applicable. You just have to somewhat set your own curricullum to the fullest extent allowed.
You won't learn alot from reading on this. Hands on practice. Cut and fit and weld different size pipes at different angles. Get a bevel square and some soapstone and a torch and some scrap pipe and get a feel for this. Oh and have fun bro

 

Sure Ill email em, you can host them if you like. Man wtf? Why do you insist on using battleship tubing? Its not gonna be necessarily stronger, but I guarantee itll be heavier.

 

Is this for looks or functionality. X-braces between diagnal corners stiffens the absolute **** out of a rollbar/rollcage.
How the mounting ties to the frame/subframe is every bit as important. In a roll if the rollcage shears loose it could end up being what kills you

 

It's for functionality. I was planning on building one like the Autopower roll bar, but adding the X like you said. I need to be able to mount a 5pt harness on it, and a camera mount would be nice too

I'll think about using a little bit smaller tube, I'll have to check what dyes we have for the bender before I order the materials anyway.

How thick should the mounting plates be, 1/8"? Or is that overkill again

 

3/16" or 1/4" on the plates. Flat material has a lot less structural stability than pipe or beam.
Depending on how you design it will decide how much stress the flange would absorb in a wreck. The shear strength of a piece of 1/8" mild steel is not that much.
When you look at a really well wrecked car that was going close to 100 MPH it is insane what happens to some of the steel. Of course there is a world of uncertainties in the event of a wreck that you just cannot be sure of. You build it as strong and stable as possible and hope you never have to find out just how well you did
Will you be welding or bolting this in?

 

I will probably be welding it in, but I havn't decided on anything yet.

 

If you are still in high school you most likly don't know how to weld even thoe the teach said your good. I've been doing this kind of work longer then most of you guys been alive. One, know what you are getting into,Two know how to do it and do it a few times befor realy trying, Like some one said your hande work could kill you or some one els , like me ,I wouldn't like that.

 

I don't have much experience, but don't worry, I can weld. I have no problem laying a nice bead with an arc welder, and after that doing some MIG welding will be pretty easy. I've been around a lot of machining work, and have a little bit of experience. My dad has been the foreman at a BIG machine shop for as long as I can remember, and I have been in there quite a few times making some random parts for my car. Actually making the cage is not a problem at all, I just needed help with the size of the tubing and the attachment points.

 

Go to the race section, I just posted pics of my cage, as did several others, you can see everything from basic to extreme. Carl Byck

 

Pictures like that are exactly what I need to see. Carl Byck's looks sweet, I may end up building it like the back half of that one.

 

I saw the carb hat , that's the wrongest way to go, resons why, when it goes in to boost the air perssuer is going to be pos down the thrut thos pushing the fuel back thruogh the jets into the bowl ( I know my speeling sucks ) and out evey seem there is along with the fuel. Most turbos use slinger and piston rings for seals and the boost it self helps to hold the oil in,but some of then have posative seals and can hold vacuum, find one of thoes good luck or build your own seal.Get a water pump and take it apart and see how this type of seal works , designe your own for a turbo and you said you had use of a machine shop , a turbo that sucks and can hold vacuum is the rite way to go

 

What the **** are you talking about??? I have been driving my car for over a month now, and it works great. I have run 16psi, not a problem at all. The car runs great, and is easily a mid 13sec car at 12psi. How is a carb hat the wrong way to go? It's the only right way to do a blowthrough carb'd turbo.

One question, have you ever actually made a blowthrough turbo setup? Have you ever even seen one in person or driven one? I bet you havn't.

 

Coldy, there are some additional elements that will be added, specifically, a bar that goes from strut tower, to tower in the rear, and triangulates with the main hoop. I will also be gusseting the cage to the body in a couple places. The tubing is DOM 1.5"x.120. This is good to ~3000lbs in most sanctioning bodies. The biggest challenges are making a cage that is as tight to the body as possible, and still allows for 360* welds. The next is proper coping of the pipes, this requires a good sense of the third dimension(how the pipes will intersect) The best approach for a beginer is to have an extra piece of tubing, experiment with that to get the cope right, and then go to your actual piece for the cage, a sacraficial 4 foot piece will save you from coming up short on the actual pieces of the cage. Good luck, Carl

 

your rite I have not ,but I know you problems with it.

 

I'm not having any problems with it.

The fuel can not get blown back into the jets, that's what the rising rate fuel pressure regulator is for. Every 1 psi of boost it sees, it increases the fuel pressure 1psi to compensate.

 

Coldy, sorry I forgot to email the pics. If you still need them, drop me an email. DC871@aol.com .

 

Is tat line perssure or bowl pressure ?

 

Okay, here's how the pressure regulator works.

You set it to a base psi, which for the nikki carb is about 4 psi. Threre is a vacuume/boost port on the pressure regulator that gets connected to the primaries on the intake manifold. So, at 0psi of boost, there is 4psi of fuel pressure. When at idle and it is seeing vacuume, it may take the pressure down to 3psi. When you are boosting 3 psi, you now have 7psi of fuel pressure. For every 1psi of boost the regualtor sees, it adds 1psi of fuel pressure.

Get it now?