Topic of Discussion TOD: Roll cage design and building

[Greg]

For the latest Topic of Discussion, we will be discussing: Roll cage design and building.

Let's specifically address: Designing a roll cage which will: Protect the occupants and maintain structural integrity during a roll. Also, let's discuss where to start once you're ready to bend and weld.


Obviously, there is alot of information to cover in building cages. From tools & materials, to triangulation and frame mounts. Please try to keep the TOD on track and we'll cover the realted stuff in another discussion.

Discuss!

 

[I Lean]

Trying to dredge up some tech again, huh?

Where to begin......gotta first decide what the intended use of the vehicle is. A cage that will save your head in a rollover but be deformed and unsafe for further rolls might be adequate for one persons use, but not others. (and not me)

Assuming we're starting with a vehicle of some sort (a jeep, say?) you'll need to determine where and what to mount a cage to. Typically it's the floor, but if it's too rusty and crappy to be solid then something needs to be done about that. Tying the cage to the frame may make it more solid. Some people like to keep the cage "loosely mounted" only to the body, but have the seats and harnesses integrated into the cage, so in a worst-case roll they are relatively safe in their "capsule" while the rest of the rig can disintegrate around them.

I'll stop with material selection, and let others chime in. (there's a TON of options and stuff to cover) The type and size of tube you select will be affected by the vehicle it's going in, the intended use, and how extensive the cage will be. Using larger or heavier tubing will need less structure to be adequate, smaller or thinner tube requires more bracing to be strong. Aesthetics come into play as wel....a K5 Blazer won't look "right" with 1.5" tube for it's cage. On the other hand, a Samurai using 2" tube will look similarly out of proportion.

My personal preference for most rigs is either 1.75" or 1.5" tube....partly just because I hate working with 2", and I think it looks bulky and weighty. I always choose DOM over HREW, because the cost increase is minimal compared to the strength benefit, especially since it is the exact same amount of work to build the same cage out of either material.

 

[Shawn]

I hate working with 2", and I think it looks bulky and weighty.

I agree, My cruiser cage is 2" and I hate it. One of the things I like the most in cage design is the out come. I have tried over and over to preplan a cage. The end result is never the same as the original design. That by far is the funest thing about building a cage. Start with a hoop and let your imagination go. That I love, seeing it develop before your eyes, creating magic, designing and trying different ideas.

God I love this hobby!!!!

 

[Hickey]

The first tool you need is an adequate weldor. A weldor is the operator of the welder. A cage should not be your first, or even second welding project. TRy some bumpers or sliders first.

The tighter you can fit your copes/joints, the stronger your joints will be.

 

[troutbum]

Couple of things I have found helpful.
-25% of the tube diameter for the correct notch depth. 2" tube=.5" notch depth
-Mock up the piece and use a sharpie to mark the direction of your notch then line it up parallel in the notcher. More than once I have scrapped tube because I notched it in the worng direction.
-I bought a clear protractor at home depot is is similar to the PBB bending 101 angle-o-meter, but it will also give you the angle measurement. I use it all the time. pic below
-wimmiter is good for angles the notcher wont do
-Hydro beats the hell out of a cheater bar

 

[Greg]

Something I'd like to address... which type of gussets are stronger, plate steel or round tube? I'd think the round tube, as there's more surface area, further away from the junction of the tube. Would this be correct?

 

[BioNuke1]

Something I'd like to address... which type of gussets are stronger, plate steel or round tube? I'd think the round tube, as there's more surface area, further away from the junction of the tube. Would this be correct?

hmmm, thats a good question, assuming the 2 types were of equal "size"

Another thing, gussets are supposed to curve and flow into each piece, not be a flat triangle

corners and other imperfections gather stress

look at how a tree branch is "gusseted" to a tree trunk, thats what you're going for, imagine if the tree branch just had a triangular shaped gusset instead of a flowing shaped one, it would break at the end of the triangle gusset

For those of you that cannot picture a tree... one is provided below, do not be alarmed

 

[I Lean]

Something I'd like to address... which type of gussets are stronger, plate steel or round tube? I'd think the round tube, as there's more surface area, further away from the junction of the tube. Would this be correct?

Strength of the gusset itself, tube is stronger. Plate is easier to buckle. Also, depending on where you put it, it can actually "slice" into the tube you're trying to gusset. Either way, some gusset is probably better than no gusset at all, even if all it does is move the bend point from the joint to the end of the gusset.

Some of the nicest ones I've seen lately were bent tube gussets. VERY difficult notch, so that's one big reason not many people (including me) do it. Pic:

That's John Reynold's new buggy, being built by Bender.

 

[Herzog]

I agree with the bent tube gussets. The load spread on those are awesome, although extremely difficult to notch like I Lean said.

 

[PierCed_3]

I hear good things about the "halo cage" but will it work and is it just as stable if you use an "a,b&c" pillar? I am in the design stages of my rollcage and I have another hoop that I was going to use for my C pillar. Other than being ugly is it stable enough for me to be able to run my family up and down the rocks and not worry about it failing? Also is the stock rollcage a good place to tie into for your frame. It has been suggested that you replace all the cage with 1.75 DOM .120 wall and not worry about it but what about the guy on a budget?

Basically I want to know if anyone has seen the stock rollbar (with cage added to it) fail. I know on Rockmonkeys old YJ it is still intact and in good shape.

Comments?

 

[RockMonkey]

I hear good things about the "halo cage" but will it work and is it just as stable if you use an "a,b&c" pillar? I am in the design stages of my rollcage and I have another hoop that I was going to use for my C pillar. Other than being ugly is it stable enough for me to be able to run my family up and down the rocks and not worry about it failing? Also is the stock rollcage a good place to tie into for your frame. It has been suggested that you replace all the cage with 1.75 DOM .120 wall and not worry about it but what about the guy on a budget?

Basically I want to know if anyone has seen the stock rollbar (with cage added to it) fail. I know on Rockmonkeys old YJ it is still intact and in good shape.

Comments?

The one on my old YJ took one hell of a beating, and held up for years.

 

[I Lean]

I hear good things about the "halo cage" but will it work and is it just as stable if you use an "a,b&c" pillar? I am in the design stages of my rollcage and I have another hoop that I was going to use for my C pillar. Other than being ugly is it stable enough for me to be able to run my family up and down the rocks and not worry about it failing? Also is the stock rollcage a good place to tie into for your frame. It has been suggested that you replace all the cage with 1.75 DOM .120 wall and not worry about it but what about the guy on a budget?

Basically I want to know if anyone has seen the stock rollbar (with cage added to it) fail. I know on Rockmonkeys old YJ it is still intact and in good shape.

Comments?

It's all good if properly braced.

 

[Ohms]

If it's braced like Carl said-You should be fine. Remember-triangulation is your friend......But there's a fine line between structure and a jungle gym. Custom cages take time to design. Just throwing tubes at a car won't make it any more safe.

 

[Tacoma]

I've got one for you buggy/Jeep guys:

If you're doing a cage in a roofed vehicle, how complete a weld can you get on a tight cage (tight to the roof I mean), and how does this affect the integrity of the cage? I would think that you can't fully weld the top of the tubes, but then you've got some factory structure there... which might not be very sturdy at all. I know that full size Jeeps basically flatten themselves, not much holding the roof up.

Is that going to have to be a compromised design somewhat, or can you usually squeeze out enough room by removing the headliner or something?

 

[I Lean]

I've got one for you buggy/Jeep guys:

If you're doing a cage in a roofed vehicle, how complete a weld can you get on a tight cage (tight to the roof I mean), and how does this affect the integrity of the cage? I would think that you can't fully weld the top of the tubes, but then you've got some factory structure there... which might not be very sturdy at all. I know that full size Jeeps basically flatten themselves, not much holding the roof up.

Is that going to have to be a compromised design somewhat, or can you usually squeeze out enough room by removing the headliner or something?

Depends on how tight it is. If it's nice 'n tight, you can't get to the top of the tubes. You do have options like cutting a hole in the floor to sink the cage a few inches to weld it, then raise it back up and finalize the floor plates and whatever....

 

[Milner]

Depends on how tight it is. If it's nice 'n tight, you can't get to the top of the tubes. You do have options like cutting a hole in the floor to sink the cage a few inches to weld it, then raise it back up and finalize the floor plates and whatever....

Also get creative in how you put it all together....weld sections outside of the vehicle and install them in such a way and order that allows you to more fully weld more of the cage....Sleeves can also be used if needed and used appropriately.

 

[Tacoma]

Thanks you guys... that's clever, cutting holes in the floor. Why not, they'll be covered anyway.

 

[flying Brian]

roll cage

This is a subjeck i know very well. I have bin building buggys for 25 years and rolled 8 of them 3 of them very bad and so i have had a chance to see the affect of rollovers and end over end first hand and i have seen a friend banged up very bad because he did not go with heavy wall tube he wanted to keep it light and it folded up on him and trapped him in his buggy.I have learned that if you think it is going to bend it will i try to X brace every thing i can or tryangels and try to gusset all my bends. I have put roll cages in baja buggs and a acuppel of rase cars and had to cut the body then weld the tube then weld the part you cut of back on you have to design well to keep from cuting the body to min. If you cant do a good job welding the roll bar dont put it in it can be very dangerus when you roll and that tube brakes luse in side with you. There is 3 things i think that is very importent to me when building roll cage is that the seats are mounted in with the cage and the seat belts and the disign of the roll gage and where to put the cigeret lighter
The buggy in the pic. is my last disign i needed all my brain cells for this one { all 3 of them }

 

[jgw50]

Hate to be the engineering geek here, but if you have access to a CAD program, and arent afraid of doing a few calculations, I would imagine you could have a pretty efficient design. I have only done this once and made a small buggy, but used a Finite Element computer program to analyze the stresses in the cage, and it was suprising where I needed to beef up, and where less was needed.

In the end however, weight isnt all that bad, and i'd rather be safe so...

when in doubt, make it stout

 

[Tacoma]

I would love a cheap FEA program... if anyone knows of one. Even a good cheap CAD program would help.