Straight tubing roll cage

I do not have a bender. Is there any reason, other than looks, that an A hoop has to be bent? In other words, can I cut 3 straight lengths and weld them in a upside down U shape, 2 legs with a cross piece on top.

Don't flame me....I really want to learn. Please only edjamacated responses...no heresay....no "I think, but don't know", responses from metal bytches will be given extra consideration.


Thanks
Rev

Wow, no responces yet?
I guess I will tell you that the more seams you have in your cage the more places for failure. Basically its like one pine 2x4 is stronger that two nailed together. Sorry for the stupid comparison, I know your cage isnt made of wood but thats the only way I could think of putting it right now.

Pat Gremillion's (sp) rig, the one with the hummer running gear, that ran in the comps the last couple years did not have a single bend in the whole chassis.

Every single piece was straight and all joints were mitred. There has been some discussion on POR about this and the consensus seemed to be -
-you could make the rig as strong as any "bent" rig
-the penalty is more tube to achieve the same strength, thus more weight, thus needing more beef for the extra weight
-you better be a damn good welder because there are a lot more welds in such a cage
-you better be an excellent fitter of parts, mitred joints in tube require some skill and a bunch of patience.

Save your $$$ and buy a bender. JD2 with a single die can be had for less than you think.

If you are only looking for a single hoop, like the one behind your seats (B Hoop), how about asking your local race shop to bend you one?

pad, pad, pad

Plus there is not much in the jeep thats straight,bending allows the tubing to follow the contours!

You will further the perseption that 4 wheelers are red-neck hill billys.

If you were totally lucky in a roll over, the force imposed on the roof would be directly in line with your upright tube legs and there would be no disadvantage. Unfortunately, that probably won't happen. Since the forces imposed on the members of a roll cage or roll bar are applied at various angles, the diagonal strength of the hoop is important. the corners and associated diagonals and gussets are responsible for this strength.

The broader, sweeping curve of the bent tube provides more material to resist bending and reduces the lever arm acting to collapse or open the bend. The material immediately surrounding a welded joint at this intersection can be brittle. With forces concetrated in a much smaller area, the joint can fracture and will suffer a catastrophic failure where-as the the sweeping curve will fail in a slower, more predictable manner. It will tend to bend, but not break, giving a little rather than snapping in two.

You can make up for the failings of the sharper corner produced by a mitered joint by adding gussets and diagonal bracing in the corners. For my money, I would find a local chassis shop and provide them with the necessary measurements to bend a hoop to your specs.

So.....

Yes it could be done.

No it would not be ideal.

Thanks, that is what I was looking for. I'll be checking for a shop.

Rev

first of all, den, don't make your cage out of pine!

that would be stupid.

I can't beleive that one guy suggested that....

make it out of maple.

the joint should be mortise and tenon or at the very least, a double biscuit.....

(damn you sewerboss!)

Can I add my buck two and quarter here??
As XJ owners we all need to remember that we are running unibodys, and anything we do to our rigs will effect how the frame/body will withstand tortional impact. Even the addition of a tire carrier will have an effect (let me not go into detail here about the swing tire carrier vs. roof rack carrier debate.)
All I wish to say here is that when we add weight to our rigs, we should tie them into the rest of the body, not just doubler plates in the floor but also tie ins to the pillers as well. When we add roof racks they should be tied into the roof support braces...when we change the location of shock mounts we need to create additional support etc. etc.
A simple loop is better than a poke in the eye with a sharp stick but........consider the entire jeep when adding....
Good luck
Rick

by the way....I can't mortise for a darn....

Jump This said:

"tortional impact."

Click to expand...

Is that like when you get hit with a law suit???

No no no....thats "brief impact"

OK, I read the thread on POR about this.....all of it...through the off-topic crap, and came up with.....

they both have strengths and weekneses. This could turn into another long-arm, short-arm debate, electric or hydro, automatic or manual...etc.

As for me....i will examine the shop idea 1st, if that does not pan out then its cut and weld. Either way, I will tie in the existing pillars to the cage.

Anything has got to be better than the way it is.

Rev

Ohhh...you would not want to build it out of Maple, I think Ash would be a better choice.

What about this;
Buy a cheap Harbor Freight 12 ton pipe bender (which I already did), modify one of the pipe dies, either by shimming a too large one or by grinding material away from a too small one, to make it the right size for tube? Anyone have success doing this? I have used my pipe bender for pipe and it works great (unless you try to bend past 90 degrees). I would like to be able to bend some tube for a cage with it as well. Local shop here wants $20 per bend and that will get pretty pricey for a full cage.

JKTXJ said:

What about this;
Buy a cheap Harbor Freight 12 ton pipe bender (which I already did), modify one of the pipe dies, either by shimming a too large one or by grinding material away from a too small one, to make it the right size for tube? Anyone have success doing this? I have used my pipe bender for pipe and it works great (unless you try to bend past 90 degrees). I would like to be able to bend some tube for a cage with it as well. Local shop here wants $20 per bend and that will get pretty pricey for a full cage.

Click to expand...

Although it can be done,the biggest issue is the radius.Pipe is bent on "much" larger radius than steel tubing.Also you can only with the heavier walls to prevent buckling.
I bought the JD2 bender and love it,leads to lots of projects!

This may be conjecture, but I'd rather have no roll cage at all than one that could catastrophically fail. A 'properly' welded joint should be stronger than the material joined, but...

In (most of) our design criteria, we need a roll bar to help the Jeep withstand a slow-to zero-speed tip over. To offer any measure of safety, I think the seats / harnesses need to be tied in somehow (not left bolted to the floor) The roll-bar in any case simply delays deformation of the interior cockpit...hopefully long enough for the rig to quit rolling and the driver/passengers to safely get out.

I may take abuse for the following statement, but I'd guess that once any vehicle is rolled 'once' that structural integrity is compromised and may not survive repeated additional stresses in any predictable way.

To fend off 'severe' impacts (such as a NASCAR racecar might see) the chassis is a rats nest of triangulated/gusseted tubing... designed to absorb the impacts by deforming (self destructing) in a controlled manner over time. Again this is a 'one-shot deal' for the chassis...it is scrapped after anything severe.

I dunno how to apply this to high-speed use in an XJ (like JeepSpeed or SCORE etc...) but in a vehicle that sees multiple-use (street & trail) I think there is a bigger risk from collision with other vehicles/fixed objects along the roadway. Every conceivable impact is a little different, but take for example Paul Travis' pre-airbag XJ that met a concrete column (overpass support) head-on at highway speeds. The Jeep wadded up around the column, and there was some intrusion of the driveline into the cabin. He didn't 'walk away', but he wasn't totally hammered either. This is a case where a super-beefy front bumper might have made things worse (transferring the impact force "faster") OTOH a purpose-built cabin protection system: rollbar/reinforced floor-firewall etc...may have let the engine & driveline squirt out underneath. But again, the extra-beef (extra weight & deformation/time factor) may have had worse consequenses on the occupants.

That said...if I were to be T-Boned on the way to work this morning, I'd rather be in a taller vehicle with rock-rails than in a low-rider with ground effects. (With luck I'd be t-boned BY the low-rider and it'd wad up into the rocker armor....lol I'd flop my junk back onto the wheels and still get to work OK)

Dunno if this made any sense...it's awful early here.

what the hell is unibody torsional impact?

that's the force exerted on a component under rotation to its failing point....

if you put a twisting force on the unibody, it wouldn't be torsional loading, each member of the unibody would recieve linear forces, tension and compression....

torsional impact is a term used with things like dirvelines and shafts and stuff.