Roll cage design recommendations with pictures

[bp71k5]

Short story is that I need a roll cage for my 71. I have a few requirements for the cage not necessarily in this order:

1. At a minimum it has to provide adequate protection for passengers in the front and rear seats during a flop or roll to either side or front\back.

2. It must be removable within a few hours to allow topless wheeling around town and general fun without the cage.

3. I want the general body lines to mimic a first gen hardtop.

The goal of the design is a well-engineered cage to protect passengers without adding weight or other features that only protect the windshield, sheetmetal, or other non-human parts. I don't have anything against protecting the body, I just want to make sure the energy and money is spent on adequate protection for me without over-engineering things.

I've spent some time searching for roll bar design ideas, cage concepts, etc and there's a lot out there for finished projects, but not as much info on why different things were done or what function a particular portion of a cage plays in a crash. There are some for high speed racing, but not as much for 4x4 or rock-crawling. Does anyone have any good links to that kind of information or recommendations?

 

[bp71k5]

Here's a quick model I've made to show what I'm thinking.

My biggest unknown issue is whether I can get decent protection without adding any "permanent" support bars along the A-pillar.

I believe it may be possible since I've seen the results of some flops where the passengers were protected by a roll bar(or hardtop) and the radiator core support carrying the load of the truck when it was upside down. The windshield may be permanently damaged, but nobody was injured.

One other less desirable option is to add some removable support bars that go between the upper A-pillar and the floor to add some support in that case. I could remove them if needed.

The blue colored bars are more for holding the appearance of the stock hard top. The red bars are some basic triangulation I thought would be useful.

 

[Hogback Fabrication]

The changes I would make to that design are in black and blue

But honestly there are a few things inherent with your design that I don't care for, mainly the basically unsupported a pillar, the b pillar being bent forward and the long stretches of unsupported tube. If you can post up a picture of that first gen sans cage I can draw and explain how I would do it (it would still be removable).

Out of curiosity, why would you want to remove the cage on any kind of regular basis?

 

[bp71k5]

mainly the basically unsupported a pillar, the b pillar being bent forward and the long stretches of unsupported tube.

That's good feedback. Is there any other way to support the A pillar than adding a tube down like your black lines? The other concerns are also well taken. Since I'm in the super early stages, I thought I'd start with what looked good and then modify it to be more functional.

Part of what I'm after is knowing where the protection should be focused along with good cage design practice. My only assumption at the moment is that a roll bar behind the front seats is probably useful, but only because I've seen so many of them. I can then add all kinds of diagonals, bracing, etc., but it would only be from "gut feel" rather than knowledge or any real world experience which is what I hope to get by sharing the ideas.

Out of curiosity, why would you want to remove the cage on any kind of regular basis?

Also a good question. Two reasons actually, the primary reason for having the truck is driving around without the top. It's just fun that way. Taking away the possibility to drive it as a true convertible would change that. In reality, the cage will only be put on for wheeling trips and bad weather.

The other reason is that I want to keep the possibility of going "back to stock" someday if needed so I want to limit the amount of permanent "damage" I do. The second reason may be moot at this point.

Let me see if I can get a clean image without any cage on it for discussion.

 

[JpEater]

I vote for the idea of building the cage completly with the A pillars. It would be a waste without them. Just build it right and when you take the top off you will just have a sexy cage to show off. The idea of taking the cage out sounds good and all but it would get old real quick. Go with the full time, always in protection.

 

[Hogback Fabrication]

I was thinking the same thing, build the cage to fit inside the top and you won't need to compromise anything.

Unless tubing makes you feel too enclosed

 

[70jimmy]

You have seen mine in person and there a bunch of pics on here of it. Just change mine so it doesn't involve seat bars since your seats would be bolted to the floor. Mine can come out with about 36 bolts and then I can just re insert the bolts and keep my sliders in place.

Now lifting it out wouldnt be fun, better have a lot of friends or a lift system like what was used to put mine in.

Sorry I'm not at my comp otherwise I would post some pics.

 

[Babaganoosh]

I created this one for another member on here, although it's for a 2nd gen I'm sure you could figure something out and come up with some ideas.

Yes the ole needs more triangulation from pirate came into the design.

 

[rdn2blazer]

Lots of pics in my thread of my cage. It's a 2nd gen but you will get the idea.

http://coloradok5.com/forums/showthread.php?t=229674

 

[bp71k5]

Here's a picture with no bars on it.

I actually have seen all of those cages and like them a lot. The problem I have with those cages is that it would diminish the non rock-crawling usefullness of my truck with all that tube. I convinced my wife to let me buy it so we'd have something to haul junk to the dump with.

Maybe I'm going about this the wrong way. If I throw out the requirement about easy removal, my even more basic question is what are the basic requirements for any cage?

Another way to ask might be...how many parts from each of those cage examples could be removed before the cage became useless? After asking that, I'm thinking that there may not be an easy answer since the protection that a cage provides can vary a lot with what happens to it in a crash. It also may be that every piece adds some structure so removing any of it might make it less "protective".

I've got a stock roll bar right now so at a minimum I want some protection for the rear seat passengers. Make sense?

 

[bigblock72]

By the looks of your requirements of your roll bar you need to take a step back and analyze what your REALISTIC goals and usage are going to be. You cannot have a effective cage that can be removed and installed in under a day, if you want an easily removed roll bar then keep the 4 point stock style. The stock type roll bar is effective in street type and mild off road use with a hard top but doesn't have the strength to even help hold the body together without the hardtop on. I'm sure you know this already but just say it to make a point.

So you're obviously ready to go to the next level off road which means running with no top or using a soft top. The only way to keep one of these wet noodle first gen bodys together long term without the hard top requires a strong roll cage that ties the windshield frame to the cage and tieing the cage to the frame. There is no way around this if you want your doors to continue closing.

I can certainly appreciate your desire to keep your Blazer in original, unmolested condition and that can be done and be able to build in the strength needed. Will it be easy to get in and out? certainly not but once removed will only leave a few holes from mounting to the floor and to the frame.

I think your design is quite nice(nice computer work BTW) and will work with the additions that Chris made, I would add small brackets to bolt to the windshield frame through the original hard top holes (they can be designed to have the hard top bolt to the cage brackets as well) and have the cage bolt to the frame behind the front seat and if you're willing to ditch the nasty rocker boxes have the cage tie in under the floor boards. The cage will add more than enough strength to be able to eliminate the rocker boxes. If you built a cage similar to what you've drawn out I don't think you'd ever want to remove it simply because it will look good and add to the looks, in fact I think a first gen looks goofy without a cage when the top is off.
EDIT, I was looking at your drwing a little closer and realized the bars sit on top of the bed side. Don't do it, if the worse happened the point loading would tear through the sheetmetal and would be almost as bad as nothing at all. If you're going to do it then it would be best to do it all the way.

Here's a link to mine.http://coloradok5.com/forums/showthread.php?t=222300&page=4

 

[rdn2blazer]

I am building my cage to bo removable. Atleast thats the plan. My cage is Floor mounted to main support areas of the floor where there is more then one layer of sheet metal, some place are tripple thick. I AM going to the frame too. It will tie together at stratigic locations from the cage to the frame. I want to be about to paint or powder coat my cage so removal is something I have tried to maintain in the build. I'm not at the point of taking it out yet, we will see. I have to get it on wheels first. It's not something I'm going to take in and out though.

 

[bp71k5]

EDIT, I was looking at your drwing a little closer and realized the bars sit on top of the bed side.

Good catch. I hadn't got very far with the drawing, but my thought there was to add a flat plate to tie the cage posts into and have the plate bolt down onto the bedsides the same way the hardtop does. Then I'd add additional supports underneath the bed rail that go down to the bed floor.

I would add small brackets to bolt to the windshield frame through the original hard top holes

Also a good idea that makes a lot of sense. I hadn't actually considered body twisting problems but it makes a lot of sense to plan for it.

After hearing some of this feedback, here's another stab at a basic cage layout. I actually think it could benefit from some side to side triangulation to help keep it from folding over in a side roll (which after some of the twisty trails I've done, seems to be the most likely direction for me it lay it down)

 

[4X4HIGH]

I would build a conventional cage with good triangulation mounted to the floor/frame and if you wanted to remove it you still could but it will be heavy (probably close to 450lbs depending on what material you go with) and it will also be awkward to remove due to needing to lift it high enough to clear anything in the way IE: rear wheel wells. That's just my .02.

 

[Big Blzn]

I've got pics of my first gen cage on my pc at work and will get them posted early next week when I get back from vacation. The cange looks real good and would give decent protection in a roll over. There is a lot of additional tubing I am going to do but just need the time and money.

The reason I am posting my response now is that you said you would like to take the cage out when you want to drive it around town. Now I have taken my rig trouugh some pretty challenging trails (nothing like the Hammers, etc) in So Cal but I feel that as much as I drive it on the street and around town it is more important for me to have protectionon the street. Of course I need a lot of cage for the trails I have been on for safety reasons but all it take is of some jask ass to cut me off or pull out in front of me on the road doing 35 -45mph and my lifted blazer with 35" tires has a very good chance of rolling. Unless you have a bone stock blazer and you drive like a granny I think it is foolish to drive an offroad blazer that is modified with bigger tires and a lift without a cage on it, especially if you have one that could be installed. I can't imagine putting my family in my blazer and driving around town with no protection in my rig and my cage sitting on the floor of my garage.

 

[bigblock72]

You'd have to add a lot of tubing inside of the bed to transmit the load to the floor and even then I worry about sheering the roll bar off at the bolts on top of the bed. Two 3/8" bolts through a piece of 3/16" or 1/4" plate isn't going to have the strength to stay together in a rollover.

It's going to be easier and more effective to have the rollbar bolt directly to the floor. If you properly design it it won't really get in the way of day to day usage, it might be helpful to strap your stuff down on the way to the junk yard. You'll still be able to slide 4x8 sheets into the bed etc. The only limit would be height, and that could be remedied by designing in a removable rear bar.

 

[bp71k5]

(probably close to 450lbs depending on what material you go with) and it will also be awkward to remove due to needing to lift it high enough to clear anything in the way

Yea, I believe it. Part of the reason for this idea came from my really trashed hardtop. It still needs many hours of work and I had been planning on refurbishing it, but then realized I'd need to store both a cage and a separate hardtop somewhere when I was tooling around town without a top. I thought by combining the two, I might be able to gain usefulness for both that way.

If my hardtop is only 250 lbs and I already cringe at the thought of having to remove it, I can only imagine what trying to get 450lbs out of the back would feel like.

 

[4X4HIGH]

Just for your calculations, 1.75" x .120" DOM weighs 2.089 lbs/ft. and 2" x .120" DOM weighs 2.409 lbs/ft. I roughly calculated a basic 6 point family cage for my rig will use about 100 ft of tubing and that doesn't account for any triangulation tube. There will be plenty of triangulation tube involved but i have no idea what that footage will amount to. Then you also have the weight of the cage plates (i bought the staked plates from Kert DIY4X) also don't forget about the weight of the fasteners.

 

[bp71k5]

but I feel that as much as I drive it on the street and around town it is more important for me to have protectionon the street.

That reminds me of one additional item I forgot about. My stock 2-point seat belts really need to be changed to 3-point at the minimum. I'd think tying a third (or fourth) point into the cage would be very useful no matter how I'm using the truck.

 

[Hogback Fabrication]

Well, I like your last rendition better. Here's a few things I would change:

First, the A-pillar is still bad. You need to end each piece of tube at a corner or at the end of another piece of tube. Attaching a piece of tube in the middle of another length of tube (like you drew at your A-pillar) is bad. Seriously, don't tie your windshield frame into the cage.

Second, moving the B-pillar back a little and adding a crossbar between the two sides will help a lot. I have a feeling you don't want to do this because of passenger space. Adding the same thing at the c-pillar will still help a bunch.

Next, gussets at each of the joints and bends will help TONS (I didn't draw in all the gussets because it would get confusing). Many cages have lots of tube that is either reinforcing the (already) strongest part of the cage or is totally unnecessary. Really, gussets will take you a long way in the strength department.


Last, attach the cage to the floor. I'm not sure if you wanted to attach the cage to the bedrails or not but its not a good idea IMO.