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Old 09-21-2009, 03:28 PM   #41
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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.
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Old 09-21-2009, 03:40 PM   #42
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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.
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Old 09-21-2009, 03:47 PM   #43
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Jesus, it's not even DOM tubing? Do you have even the slightest idea of what you're doing?
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Old 09-21-2009, 03:49 PM   #44
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A roll bar or cage is probably the one item I would never try to fab myself. Its one thing to **** 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.
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Old 09-21-2009, 03:51 PM   #45
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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.
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Old 09-21-2009, 03:56 PM   #46
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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.
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Old 09-21-2009, 04:12 PM   #47
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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"
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Old 09-21-2009, 04:30 PM   #48
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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.
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Old 09-21-2009, 04:39 PM   #49
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^ does this go all the way down by the frame? also what kind of tubes aree they using
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Old 09-21-2009, 04:52 PM   #50
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Quote:
Originally Posted by ls1motorsports View Post
^ 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.
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Old 09-21-2009, 04:53 PM   #51
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ic. i thought they just bolted it right to the package shelf
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Old 09-21-2009, 05:11 PM   #52
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Quote:
Originally Posted by ls1motorsports View Post
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.


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.
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Old 09-21-2009, 07:33 PM   #53
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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 ****** 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.
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Old 09-21-2009, 08:07 PM   #54
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in for epic fail
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Old 09-21-2009, 08:35 PM   #55
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Quote:
Originally Posted by relte View Post
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 ****** 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.

advice on where to buy dom, which wont rape my wallet?
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Old 09-21-2009, 08:58 PM   #56
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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 ***.

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.
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Old 09-21-2009, 11:22 PM   #57
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^ 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
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Old 09-22-2009, 12:12 AM   #58
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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.
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Old 09-22-2009, 12:37 AM   #59
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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....
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Old 09-22-2009, 12:57 AM   #60
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Quote:
Originally Posted by ls1motorsports View Post
i thought they just bolted it right to the package shelf
aka, you haven't searched much.

The weird thing is I don't think we give this much **** 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.
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