Roll cage design lessons learned?

Nvrstuck, just hope you are not in one of those EBs if the time comes to put a cage to a real world test.

I like this post! So is there a really good cage out there to use as a starting point? I think I can add some additional support. Digger I noticed your design uses flat metal at the door pillars I assume that is so you can bolt the cage to the pillar/kick area.

I see so many Bronco out there with skimpy roll bars, I want to build some thing that still allows me to get into the truck without climbing over a tube, but I think more lateral strength is a must.

Jamie Chriss said:

I like this post! So is there a really good cage out there to use as a starting point? I think I can add some additional support. Digger I noticed your design uses flat metal at the door pillars I assume that is so you can bolt the cage to the pillar/kick area.

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Yes. The picture was screenshot during the preliminary work and doesn't show all the elements of the final cage.

The flat plates were so I could retain access to the glovebox and E-brake and provide more knee room. They are tied to the floor, the kick panel, dash and the windshield frame for lateral support. The plates can support the stress of the vertical load, but rely on the kick panel, dash and windshield tie-ins to prevent buckling. The kick panel tie-in has a provision to add a tire intrusion bar to the footwell area that I see more and more on newer trucks.

68ford said:

Who here has access to solid works and can stress test a 6 point cage like practically all of them, zero lateral support. Then draw in an X behind the front seats and see how much stronger it is. That would end this argument all together.

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I did that early on in my project. It was pretty horrible. The un-braced cage moved laterally ~12" IIRC. Honestly the results were very inaccurate because the cage was well beyond it's elastic point and could only be modeled with non-linear analysis. (very time and computer intensive)

One thing that really improved my cage was tying to the beltline in 6 places. I had to model it as an elastic support since the sides are not completely rigid anchors, but it got the cage much more passable.

Digger, and anyone else, Can you please post pictures of your cages that have had the computer modeling? I need visual cues so I can make mine safer. I'm interested in these tire intrusion bars as well. I learn visually, please post some pictures. Love this open collegial discussion.

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74 Bronco Billy said:

Digger, and anyone else, Can you please post pictures of your cages that have had the computer modeling? I need visual cues so I can make mine safer. I'm interested in these tire intrusion bars as well. I learn visually, please post some pictures. Love this open collegial discussion.

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https://waynesbronco.shutterfly.com/421#468
Min was partially drawn in solidworks but changes had to be made to make it more user friendly. Angled tubes behind the headrest were not used because headrest hit them. I also did 1 angled door bar instead of a flat one because I did not want to climb over it. Being a half cab created it's own set of issues.

68ford said:

https://waynesbronco.shutterfly.com/421#468
Min was partially drawn in solidworks but changes had to be made to make it more user friendly. Angled tubes behind the headrest were not used because headrest hit them. I also did 1 angled door bar instead of a flat one because I did not want to climb over it. Being a half cab created it's own set of issues.

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That's dead sexy there.

74 Bronco Billy said:

Digger, and anyone else, Can you please post pictures of your cages that have had the computer modeling? I need visual cues so I can make mine safer. I'm interested in these tire intrusion bars as well. I learn visually, please post some pictures. Love this open collegial discussion.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Click to expand...

A pillar foot in progress



Bare Cage with all attachment points.



Installed



Windshield braces. I triangulated this to give lateral support as well. This reinforces the windshield to the cage and vise-versa

Safer Broncos... so I live in farmland and our road off our driveway is 2 lane and 50 mph...I'm turning into my drive (1200' long so its just a gravel drive) and a lady (suicide door T-bird) rear ends me the WSP estimates at 60mph... rolls me through my barbwire fence and across my driveway.

My 20'x3/8" logging chain (no tow straps back then) is wrapped around the strg column, my 35lb toolbox is on the floor btw my pedals and the seat. Castrol 20/50wt is dripping on my dog and I...I"m not hurt at all because I had high back bucket seats and was strapped in...

My Bronco was our DD and we had a backup car so we put appr 25K/yr miles on it...kids always in it...

I put HIGH BACK BUCKETS in the back to keep their necks from getting snapped if it EVER happened again!

Getting rear ended is 100x more likely than rolling over and over and over down some road...

We want safety and this is probably the easiest thing to do... I already had a 4 pt cage...within a couple years I had a 6pt tied into the frame...

Put in high back bucket seats for your kids in the rear or take the dang stock seat OUT... it's not safe for anybody...

The other thing to do is NEVER leave tools, snatch blocks, clevis hooks or ANYTHING in the back that is not secured...ALL my tools and crap are secured in two custom metal boxes that the rear seat is attached to. The seat belts and high back fold and tumble seats (kids are gone and so are the individual buckets) are attached to these very sturdy steel tool boxes.

BTW...ditch the bomb under the drivers seat too...nothing like a gas tank under your butt...remember what Chev went thru with all the lawsuits with people burning to death from saddle tanks...

Be safe guys...protect your families....

68ford said:

Who here has access to solid works and can stress test a 6 point cage like practically all of them, zero lateral support. Then draw in an X behind the front seats and see how much stronger it is. That would end this argument all together.

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I don't believe there is any argument, we all understand, we are just trying to do the best we can that fits our needs. From what I have seen from the posted pics is ANYTHING is better than nothing with varying degrees of better. Just my .02

This has gotten me to rethink everything! I really like Diggers cage, I do think there should be more lateral support behind the front seats. I asked the question earlier is there a workable frame being sold that would be a good starting point and then add structure support from their instead of building one from scratch.

^^^^^X2, just bought a Bronco Bob roll cage, wondering how I should modify it to make it much safer for the mainly streets I'll be using it on.

I think a standard 6 point cage with added structure is fine for most people. now if you want to step up then you have to start thinking halo tube designs.

Check this out and click on the video clip.

https://bcbroncos.com/shop/interior/roll-cages/75-00111-bc-sport-roll-cage-for-early-ford-bronco/

Rustytruck said:

I think a standard 6 point cage with added structure is fine for most people. now if you want to step up then you have to start thinking halo tube designs.

Check this out and click on the video clip.

https://bcbroncos.com/shop/interior/roll-cages/75-00111-bc-sport-roll-cage-for-early-ford-bronco/

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Even that one has no side to side diagonal support and could simply fold over.

Great discussion guys!

For whatever its worth...

I've experienced the extreme terror of rolling my Bronco, with a passenger, and having the windshield fold on top of us, before the ground smashed both of us into the foot wells, the second time around. This was with a 4 pt. roll bar, at @ 40 mph on a dirt trail... nothing compares to hitting the folded windshield and the ground with your head and feeling your seat compress you (as the truck settles up-side down [bikini top]) into the foot well... I literally thought I was going to get pancaked into a pile of blood and bones. If not for the luck of slipping past the steering column (the steering wheel bent completely inward, toward the dash, from the force of me holding on just enough to give me the room to slip past) in that split nano-second, I honestly don't think I would have survived... The steering column almost impaled me, right through the chest...

So I write this with extreme gratitude to be alive and feel compelled to add my voice to this discussion about safety, for the benefit of everyone... Some may disagree with my thoughts...that's fine...I won't disparage you for trying to keep your family safe...as I certainly do not consider myself an expert or believe that I have built the best cage out there... But, it's the best I could do, given my real world experience with roll overs and current reality...

I learn something new every time I come here, and this is no exception...

With regard to roll bars and/or cages, I'm sure everyone would agree, there are many variables and factors that go into a strong roll cage while having the safest environment around you during a roll over is also very important...
You can be protected by the roll cage, and have your 30 lb. tool box kill one of your occupants... as nvrstuk has pointed out...

This conversation seems to be focusing on design, But...

The design is just one aspect...We know 6 pt. cages are going to protect you more, due to the A-pillars being present...preventing the windshield from folding over. Triangulation within such a design is important for strength...

I personally considered escape routes in the design I created, to ensure I and my family had ways to exit the truck while up-side down or on its side with rocks/walls/barriers around us. I also considered the prevention of large rocks, traffic barriers, and such from intrusion into the seating area. In my experience, once I realized I and my passenger survived the roll over ...the next terror came when I could not get out and I could hear, and smell fuel pouring out the tank. I could not imagine how more terrifying it would have been if I had a secondary tank directly over me pouring fuel on me, with a hot engine/headers in very close proximity...

Material:
DOM tubing was an absolute requirement as it will resist folding over or bending much more than mild steel. I would venture to guess that the pics of the folded cages (previous posts) were that of mild steel tubing (the wall thickness is questionable?)... In this situation, budget should never influence the decision to use mild steel tubing instead of DOM tubing. Never decide to save cost at the expense of your safety or that of your family.

Welds and fitment:
How it is put together and how well the pieces fit impacts its over all strength.

Base:
Even though the (4pt.) roll bar did not punch through the floor in my experience (thank GOD!)... I do agree that this issue should not be left to chance. If not tying it to the frame, find a way to make the base large enough to prevent it from punching through the floor or tie the bases together which essentially makes a sub-cage under the back seats, as I did. My design ties B and C pillars together, just under the bed rail . It also ties all 4 bases (B & C pillars) to each other essentially making a sub-cage under the back seat.... making it impossible to punch through...

Environment:
As nvrstuk very succinctly explained ... take a look at what you have stored in your rig and how they can become projectiles in a roll over. I removed my second tank years ago, not for this reason... But, nvrstuk's point regarding the placement of the tank makes me happy I did...

Seat restraints:
3 pt. seat belts at a minimal for all (including back seat) occupants. I also agree with nvrstuk, that high back seats and headrests help tremendously in rear end collisions and thus have those in my build. My children and wife (sometimes) ride in the back...They are my world...My truck does not move an inch unless I wholeheartedly believe they are as safe I as can keep them.

Fire extinguisher:
Mandatory...You should be able to reach it from your seat... (Front and back seats)

My point with all of this is that roll bars/cages should be viewed as just one piece of a safety package, that consists of multiple pieces.

Wishing everyone safe travels...

Aloha

FWIW DOM is mild steel. CREW & HREW seamed tubing is usually, but not always, 1010 alloy where DOM is usually either 1018 or 1020. So DOM has two things going for it that make it harder to bend; it is cold worked from being Drawn Over a Mandrel and the alloy it is made of starts out with more carbon than does the steel HREW/CREW are made from.

AND DOM is NOT "Chro-Moly", not even close. You'll know the difference when you're used to manually bending DOM and you stick a piece of 4130 in there.

Just to add to ntsqd's post, CREW, HREW are just pieces of sheet metal, rolled into a tube and welded. "CR" means cold rolled, and "HR" means hot rolled, indicating the finish of the sheet metal used...they're both low-carbon mild steel. In general, CR sheet will have a tighter thickness tolerance than HR, and a better finish. DOM tubing typically starts out as 1018/1020 CREW, which is then drawn over a mandrel to remove the internal weld flashing and provide uniform wall thickness and more uniform strength properties.

I've noticed that a lot of the CREW and HREW catalogued by the steel companies will list 1010 alloy, however generally have an asterisk regarding minimum carbon content meeting or exceeding 1010, so I would not be surprised if most of it was 1018/1020 anyway. The last few batches of your run-of-the-mill A-36 mild steel I've purchased met the same requirements of A-572 high-strength, low-alloy steel...go figure.

nvrstuk said:

Safer Broncos... ..

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Brian we are on a similar page and that is what is driving the cage at this point, I need upper anchor points for the rear seat belts for the newly installed JK rear seat.

I was hoping this would not turn into a "If you don't tie it into the frame it is useless" or "If you don't make it out of 500' of 2"x.250" Chro-moly like the trophy trucks don't waste your time..."

Fatalities from being crushed are far less likely than whacking your head on something statistically. Jaromy's cage does the best job of addressing this from what I have seen and is pretty similar to what we drew up.

I and the other I am working with on this project do not want to cut our dashes or impede the usability of our trucks, but I do appreciate the input on how each of addressed your individual concerns.

There is no doubt adding lots of triangulation and frame tie-ins will stiffen the structure and make it stronger but at a cost... The extra weight up high increases the chance of a roll over, and a stiffer structure will dramatically increase the amplitude of the crash pulse.

I fully expect my cage to deform in a high speed accident but I just don't want it to fail. Fortunately, nearly all the roll over images I have seen even with a basic Smittybuilt style of roll bar they have not failed completely. With that in mind a cage that ties into the body in several strategic locations, built from quality materials will increase the safety of the vehicle in a roll over as long as we don't whack our heads on the cage.

Please keep the constructive feedback coming.

Regards, Tony

Totally understand Tony...at one time after owning a 6pt cage that at best made it difficutl to climb in or out i built another 4pt and tied it into the windhield frame...an engineer friend of mine saw it and immediately explained why it wasn't much better than not having it tied in..
SO I came up with this...very minimal day interference other than the glove box and since I rewired it soon afterwards and recovered the dash face...it was a no brainer for me. It's not an S curve and it is never in the way...

A reminder:

https://jalopnik.com/man-dies-after-crash-in-home-built-honda-civic-based-ka-1825681533