roll bar build
 

this is just a picture of what i made last night.... i figured i'd atleast do something to keep me busy while doing my engine rebuild....ill post more pics as progress comes along. My bar is 1.25 inches. i dont quite remember the wall thickness but its damn thick enough that it didnt crumple like a soda can when i used it on this cheap hydraulic pipe bender. I first tried exhaust tubing to just get a feel for the bender. but it got squashed. In this picture i just sized up everything to make sure the width of the hoop contours the hardtop just right.

So what kind of piping did you use? Mild steel? Stainless? What thickness? If you could shed more details that would be great.

Im going to build my own as well, and this might really help me and others out:)

i used ridgid steel piping. ill take a picture of the piping wall thickness with a ruler ontop of it for comparason . give me about 10 mins

I finished up my bar a few weeks ago. Are you going to weld it in or bolt it?

I planned on bolting mine in but I'm a lazy ass so I just welded it in lol.

^ definatly welding it in. right behind the seats, i still need to figure out where to weld plates at for the bars that go straight back.. Do they go somewhere by the rear shock tower?.. 18psi . i lied, and so did the sticker. It says 1.25 tubing but its definatly much bigger than that on the od or even the id. the pipe's wall thickness is 3/16. I made the main hoop out of 2 peices of piping. So, in the picture above, there is a gap. i filled in that gap by patching it up with piping welding it solid and grinding the welds down, then sleeving it. (pictures below) I definatly did not want this portion of the hoop to be a weak point so i put a preety long peice of rod inside half of the hoop, welded it to the pipe, then slid the other half of the hoop onto the rod, welded it onto it. Then the patch, then grinding, then sleeve.

sorry for the shit quality pics guys, but this is all that my phone can provide :(

FYI, that won't pass any type of real tech inspection. Main hoops ALWAYS have to be a single bar.

^ no worries. I dont plan on auto xing this car. Just mainly personal safety. Im sure the rod inside of the hoop, welding the seam shut, then sleeving the seam is much stronger than one solid piece. But, i could be wrong. i dont understand why it wouldn't be stronger

id be careful with that... give it a try before installing it in a car. just in case, you know?

How are you planning to build it within regs for head to bar spacing? It's gotta be a close call between not being able to fit it under the roof and keeping it 2"(IIRC?) away from your helmet. Can't really hammer it if it doesn't fit right. :D

Yeah I'd roll the car over atleast once before trying it with you inside it.

for now im only doing the back portion. I dont think i will be doing a full cage as that may prove to be more dangerous for a street application. if this is what you meant by the head to bar?. but i have the bar sitting behind the seat as possible and as high up to the roof as possible. Im using the design of miatacage.com, where they use plates onto the frame to weld the main hoop in. then two down pipes to the rear, then a diagonal section in the hoop... ehh instead of trying to describe how it will look . check out miatacage.com :)

the walls of the pipe are nearly twice as thick as miatacage.com. it had to be. If i were to use .095 (walls thickness) this bender would just have flattend the tubing. they are able to get away with using thinner walls cause they probally have godly mandrel benders. Dom - drawn over mandrel i believe is what that is called. Mandrel = no bottle necks to ribs, no crushed tubing. .1875 walled tubing+ cheap hydraulic bender = same thing.

oh haha in the first picture. you can actually see what that bender did with exhaust piping look to the right of the engine stand. that tubing just crumbled under pressure

:bowrofl:

I wouldn't let that touch my car. And my car is ugly as crap.

^ its ok. Im sure no one would touch your car. Not here for your guys criticism. just here to give some outlines on people who want to make their own bar. Its up to them if they do it in one peice or 1000 pieces

im gonna say it now: youre an idiot. dont put that crap in your car.

why not just make it out of PVC since its only for show? Did Helen Keller weld that?

A false sense of safety is better than nothing? Is your next project going to be a Papier-mâché helmet?

Good luck with that.

so for all you thread bashers, who have nothing better to do than say stupid shit. shed some light and tell me exactly what is wrong with this hoop. I would like to be enlightend by the pros, who know piping, on how "unsafe" my hoop is. Y8s can you tell me why this is crap? where exactly is the weak point in this bar?. Also why is this bar much more inferior than the ones that are made on a jig and are dom? as far as im concerned. this tubing is far more thicker and stronger than what miatacage has.

In engineering terminology:

You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).

Make the main hoop out of one piece. Yours wiiillll bend.

in your opinion, do you think that it is still not going to be strong enough even though there is a solid rod on the inside of the bar that connects the two halves, all welded together so there is no seam, then sleeved?

another question about roll bars/ cages. i dont really know how to explain this. or ask the question, but, comparing my seam which is solid on the inside and sleeved, and comparing another portion of miatacage's cage (where the overhead bars,(the bars that go through the dash and up the a pillar), weld to the main hoop) how strong is that seam? granted it is connected by the area of the dead pedal and connected to the main bar, how strong exactly is it that thoes welds just dont break off and you have this bar come crashing down on your face?

The problem is where the outside bar (sleeve) ends....you are creating a moment about that point (on both sides of sleeve) which will cause failure. It is "stronger" in some directions, but could fail -in dramatic fashion- under the right circumstance.

Consider the outside points of that hoop (which bolt to car) as the end of a lever. You have created a leverage point at that joint which would not be there if it were a seamless piece.

The bends at the sides of the hoop are the failure method for a roll bar. A gradual, mandrel bend with predictable failure which can take a lot of energy and do not break violently until WELL beyond their design range.

That sleeve joint in not only a THIRD failure point, but one which has a poor failure mode. It will take a good deal of force to break, but will not deform in a predictable fashion like the bends. It may bend as little as 10* before it shears in fast fracture failure. This would be bad.

In reality it may not happen, but it's a poor design.

Different stresses, different application.

Those bars tie in two members to form a complete frame, and only see axial loads. There are normally not moments created about those until the frame as a whole has already failed it's designed purpose.

Those sleeves are also necessary for assembly....yours are avoidable...and should be avoided.

Just because you can doesn't mean you should.

thanks for some engineering enlightenment godspeed. i appreciate it

Thanks for listening to reason instead of running off puffy eyed like a lot of the ignorant hard-headed newbs we see around here.

It's one thing to have a bad idea, it's another thing entirely to not listen to the advice of others on how bad that idea is.

Stick around...keep learning...all those guys bashing you on page 1 can help you learn a LOT about making a fast Miata.

heres a visual, made by helen keller and her paper helmet

yeh there are some people, like you who are actually willing to give encouraging advice, other than just straight bashing

that's a little better, and honestly would work...but it's bad practice, and easier to buy a longer bar and bend it.

You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.

What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.

i mean split time said he wouldnt let it touch his car. I mean after seeing his car i would have said why even run with a front bumper cover?

yes i did think about this^ when it comes to a roll. i didn't want that bar creating any more stress on the bend and rip clean out so i cut and positioned accordingly

but just to put this out there, where the seam and sleeve are positioned, it is completly solid .

Also consider that all this sleeve-jointing and inside-barring is adding a lot of weight at your roofline, which raises the CG of your car, and will have an effect on handling.

If you think that effect is small then you probably shouldn't own a Miata, or atleast not one modified enough to need a rollbar. I just swapped my carpet, and drove a few weeks sans rollbar and passenger seat, almost every day with the soft top down.

It was a whole different car.

oh yes i know. Hopefully being how low my car is, it can offset this. i have to roll onto 2x4s to get scissor jacks under it

but non the less i will take that and many other things into consideration along this build

It looks like you have plenty of tubing...why don't you just make another single bar hoop?

You could use the tubing from the first hoop you made as support bars.

i will probally end up doing that. or if for some odd reason, i am compelled and feel that this is stronger, then it might stay. Being bashed on or not bashed on, i dont really mind. like i said. its just kinda a way for others to see how to make their own. Depends on them if they do one continous bar, or reinforced to the max bar. but like i said. twice as thick as miata cages tubing. we'll see how it goes, should i ever roll, ill be sure to make a post ,if im still alive.

You should redo the main hoop fasho. I wouldn't want that big ugly sleeve on my bar everytime I walked outside to get in my car.

Also, paint it orange when your done.

That tubing had better be larger than 1.25". Every sanctioning body out there requires at least a 1.50x.095 (might be thicker, not sure) DOM tube. Bars must be 1.75x.120 DOM.

Roll bars and cages are not something you do yourself, especially if you're considering using a sleeve on your main hoop. If I were an instructor, I would refuse to ride in your car on a track. Not trying to bash, just letting you know that what you're doing isn't safe.

heres why i think its crap:

1. the material is probably not nearly as strong as the DOM seamless steel used in rollbars. how dou you know it wont split along its length in a crash and open up like a floppy taco?
2. welds compromise the strength of the material either by insufficient penetration or by heat cycling
3. you are adding a lot of weight (solid rod plus sleeve on tubing that is too thick!?) WAY above the CG of the car. Go watch a bus corner sometime.
4. you have no way to know how strong it is until youre crushed under it
5. it will not pass any kind of inspection if you ever decide you do want to take it somewhere that cares
6. a false sense of security is far more dangerous than known unsafe conditions.
7. when all is said and done, did you really save anything?

It's pretty obvious that hundreds of thousands of people have tested and developed the specifications for car safety equipment. There is a reason for the existence of roll bar standards.

If you do go ahead and build this thing anyway, be prepared to die in a crash. Be happy if you dont.

Jesus, it's not even DOM tubing? Do you have even the slightest idea of what you're doing?

A roll bar or cage is probably the one item I would never try to fab myself. Its one thing to fuck around with manifolds and exhausts, but not a roll bar/cage.

Even if your doing it simply to have something to do and kill time.....I would say its not worth it. Buy one and make something else. :2cents:

DOM is how the straight pipe is made. Tube is mandrel bent (mandrel inside pipe), while pipe is bent using external dies only. The tooling to bend it is not that expensive. JD Bender

I think HF even sells something like it for about the same price as your hydraulic bender. May not work as well as the JD one but if it's only for personal/1 time use should be ok.

Split time said he wouldn't let it touch his car because of all the many reasons given to you by EVERYONE. It is just not a wise design and as a rollbar is meant for safety... what is the point in doing it wrong?

And make fun of my bumper cover all you want... I haven't run across you out on track... and I enjoy running ambient air into my engine.

DOM = Drawn Over Mandrel. It is not a bending method. (and my mistake, it is not always seamless)

the mandrel is a straight mandrel. the tubing is drawn over it to cold work and improve surface finish and dimensions. very different beast than "regular old steel"

This is the only DIY rollbar i've seen that i'd actually put in my own car:

Custom Roll Bar Build - ClubRoadster.net

Take note of how the main hoop is constructed.

Most of you have prolly already seen it.

^ does this go all the way down by the frame? also what kind of tubes aree they using

they are using 1.75" DOM tubing. It is a copy of the HDHC design, it shows where they attach in the thread: behind/beside the seats and then the rear supports through the shelf.

ic. i thought they just bolted it right to the package shelf

This is the reason I've devoted seven goddamn posts to this thread....so you don't show "others how to make their own" in this fashion.


y8s and Sav brought up a very good point: MATERIAL SELECTION

I assumed you had picked some good bar, but any tubing off a fab rack isn't going to work. At my last internship I had to spec a lot of steel section...and there are DRASTIC difference in their construction and properties, even for parts that look the same coming off the truck.


If you don't know what you're doing...buy something from someone who does...and sure as hell don't try and "teach" anyone.

DOM is a hell of alot stronger than the stuff you are using. That stuff almost looks like large diameter conduit. LOL.
Seriously don't do it.
I was the co-captain for our SAE Baja buggy team my senior year in college and had to learn alot about DOM materials and the strengt of roll cages and tube frames.
The most important part is the material selection. Don't go less than 1.75" DOM .120 wall. I think thats the SCCA requirements for the Miata's weight and works for most organizations. The only place I have seen smaller stuff allowed is for the 24-hr of Lemons where they allow 1.5" DOM tubing for cars under 3000lbs.
I was under the impression that DOM is usually seamless too which makes it a more stable material to consider in a application like a roll bar where you want it to display consistant properties throughout and not just fail at a seam or a weld.

Sencondly you want to minimize the welds in your cage or rollbar. Now that I think about it almost every rule I have read about rollbars require a continuous loop with no joints. Even though you think the rule makers are pricks some times when you are building a vehicle to meet spec, they do have a reason for making these rules.

Lastly look at your attachment points. You can have the strongest bar in the world but if you mount it in weak areas and with inferior materials and lots of welds to introduce stress concentrations you are really hurting yourself. Just cause a joint looks real strong and beefy, it could cause the whole tube to fail right next to the weld due to heat treatment even though the weld itself could probably hold a tank.

I have to admit that I am probably one of the cheapest bastards out there, but I would not reccommend that you mess with this stuff if you do not have experiance. If you have some welding experience, the right materials and a good bender I would say go for it. Till you have all those things, go ahead and play around with the welding and stuff to gain some experience, but please don't use it in your car thinking that it will make you safer.

That bar is suposed to help you in a wreck, but imagine that sucker braking off in a collission and it actually injuring you for no damn good reason.

in for epic fail

advice on where to buy dom, which wont rape my wallet?

You would have to check your local yellow pages or google for steel suppliers in your area. Some racing shops might be able to hook you up. We had to travel almost 2 hrs to get some relatively cheap DOM tubing for our buggy.
I think we could have gotten it through the local steel suppliers but it would have been a special order item.
Honestly you will probably spend at least $100 or more just on the DOM. Actually I don't remember what the 1.5 or 1.75" DOM costs. We built our buggy out of 1" and 1.25" DOM.

LS1, what is your motive for building this rollbar? If its just for looks, get a style bar, they would both be useless. If you really want to build a bar that will serve a purpose, go make some friends at a racing shop or somehwere that does this kind of stuff. It is easy for someone to give you advice oline that could potentially get you killed (especially in this case), but its easier for someone to help you out in person to make sure you get things done right.

I wish more people would take the time to learn how to do things and then do it themselves. The problems is when people that do not know how to do something, just jumps in does something and hurts someone. Its ok if you hurt yourself when you do something like this, but what if your girl, wifie, kid ect. gets hurt in your car because of a defective bar?

Take your time save up for a proper bar. If you are on this forum, I know you like to "drive" your miata, I know I do. The average miata driver is probably much safer than a SUV driving soccer mom, but i sure like having that sturdy rollbar begind me when I have a soccer mom tailgaiting my ass.

One more thing. Not only is the rollbar a safety item. When done right it will greatly add to the stiffness of the car. My miata was transformed after Hard Dog install.

^ agreed. The car will most likely never hit the tracks. i do plan on making this a solid one piece out of dom as well as the other piping for it. the over all design will still be the same as miata cage. Just not a full cage. Just the main hoop and down tubes. with some triangulations

If everyone isn't circle jerking over your "fabrication" the first reaction shouldn't be to throw a hissy fit. Peeps b hatin because they see real problems with what you're doing. Calm down, find your shift key and spend some time reading and learning.

:cjerk: that Fail bar is awesome!!! Seriously listen to everyone.... there telling you what is wrong with it, if you don't want to listen why start the thread????? trust me....... redo it....

aka, you haven't searched much.

The weird thing is I don't think we give this much shit to the people with the chrome double hoop ebay style bars, weird. Please, for safety, looks, and peace of mind do not use this roll bar.