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post #1 of (permalink) Old 02-12-2002, 09:48 PM Thread Starter
 
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Roll Cage

Well I finally got the 220 hooked up so I can weld now.
Got a tubing bender yesterday.
Got 42' of 1 7/8" OD schedule 40 tubing today.
Played with a couple first bends to see how the bender works on this stuff.
Cut a length of pipe to fit in the CJ-2A.
Put two bends in it.
Took it out to the Jeep to check and see how it fits.
Cut 4 1/4" off each side to shorten it and voila!!!
I now have the rear hoop 90% complete.
All I lack now is to get some plate steel to make the feet out of.
By tomorrow afternoon I should have the feet welded in place and the rear hoop bolted down to the tub.
Next I will bend the front hoop and weld the feet on it.
After that I will cut the four spreader bars and two diagonal pieces for the back.
My only problem with the spreaders and diagonal pieces is I do not have a tubing notcher.
I guess I will have to borrow one or buy one, but at any rate It has come to the time when I finally get this thing built so I can take it wheeling in more extreme terrain than at my deer hunting camp.[img]/wwwthreads_images/icons/wink.gif[/img]

On the welds, is it better to make one thick pass, or should I make two lighter passes over the joints and at the feet?
All this time I thought a cage was difficult to build, but it seems fairly easy so far.
I do plan on tying it to the frame, but that can wait for a later date.

Take Care and do some good wheelin' for me.



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post #2 of (permalink) Old 02-12-2002, 10:38 PM
 
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Re: Roll Cage

What kind of Bender did you get?

On the notcher, you can get by without one if you can keep all your mounts at 90 degrees or there abouts. When you start getting into compound angles, that's where things get interesting. When we did mine, we did all of it with holesaws and an angle grinder. When you get a holesaw, get one of the bimetal lifetime guranteed ones Home Depot carries the Blu-Mol Agressor line that's pretty good. Also if you don't already have a GOOD drill (5 amps or better) I would invest in one for this project, it's a good way to burn up a cheapie drill.

The holesaw/grinder technique requires a little more patience, and remember LITTLE bits at a time, you can always take more off, you can't put it back.

On the welds, take your time, lay down a nice deep bead. The key is a solid weld with good penetration. If you don't feel you're getting it in one pass, then try multiple passes, this is really going to depend on the capabilities of your box.

Another piece of advice. Weld as much as you can in the Jeep. Be careful to cover glass, upholstery and anything else that will burn. Once you have that, remove the cage, BRACE the feet and such with wood, and finish welding. This way you will minimize warping as you heat the joints.

'83 CJ-7 nothing original but the tub and axle tubes
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post #3 of (permalink) Old 02-12-2002, 11:06 PM
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Re: Roll Cage

I hate to break the news to you, but schedule 40 is PIPE not tubing. Big difference. And is not suitable for a roll cage.

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post #4 of (permalink) Old 02-12-2002, 11:43 PM
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Re: Roll Cage

Bob, Why is SCH40 pipe not as good as tubing? I have posed this question many times. I have looked at the material properties for a number of different ERW and seamless pipes and tubes and when you boil it right down to the math, there is not a lot of difference. Yes there are some types of pipe that should not be used, but there is a lot of pipe out there that can be used. The ERW pipe if you pick the right material spec. is just as strong as the ERW tube. The main difference that I can see between the pipe and tube is the wall thickness, and the pipe is usually thicker for for a given OD. I work as a mechanical engineer and I have spent quite a bit of time looking into material properties. Unless you can prove otherwise, I say that properly spec'd pipe is every bit as good as the more expensive tube, and a lot less expensive. I have presented this arguement in a number of forums, and have yet to be proven wrong. If you can present me with data that specifically states that pipe absolutely cannot work for a cage, I would be glad to look at it. As I said, I have looked into the tube vs. pipe arguement on numerous occasions, and I cannot see why pipe cannot be used for a cage. I am not sure where the pipe cannot be used for a cage myth started, but no one has yet to provide evidence contrary to my findings. If you compare ASTM A500 tube, which is obtainable in pipe sizes, to the more expensive DOM tube you will find that the material properties are very similar. For that matter you can even compare A53E/B pipe to tube and you will find that the yield and ultimate strength values are very similar. The key with pipe is to make sure that you do not get the butt welded pipe. All the literature I have seen indicates that the butt welded pipe does not fare well in forming operations. But the ERW pipe forms just fine. I have seen cages built from ERW tube, and no one seems to take issue with it, but as soon as someone says "pipe" people start freaking out. Nomenclature has nothing to do with physical properties, pipe, tube, no different if you spec your pipe properly. The only real penalty I see with pipe is the extra weight from the thicker wall. Feel free to email me if you have any data that supports the tube over pipe theory. I think it is all hype and there is nothing wrong with pipe!

Cage Up, Wheels Down
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post #5 of (permalink) Old 02-12-2002, 11:59 PM
 
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Re: Roll Cage

JeepFiend: Dumb question (and ultimately why I opted for tube)... With Sched 40 and the pipe you are referring to, isn't it quite a bit heavier (weight-wise) than it's comparable tubing counterpart?

Just curious. I don't profess to know anything about metallurgy, or structural design. But I did stay at a Holiday Inn Express last night, I DO have a welder, and I'm NOT afraid to use it (please stand back). [img]/wwwthreads_images/icons/laugh.gif[/img]

'83 CJ-7 nothing original but the tub and axle tubes
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post #6 of (permalink) Old 02-13-2002, 12:19 AM
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Re: Roll Cage

It would be heavier. Since it has thicker side walls, woouldn't that possibly make it stronger as well?

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post #7 of (permalink) Old 02-13-2002, 08:55 AM
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Re: Roll Cage

It is typically heavier. The 1-1/2" Sced. 40 pipe has a 1.9 OD and a .145 wall. A lot of the cages I have seen use a 1.75" OD tube with a .120 wall. The tube will weigh about 2.089 lbs per ft., while the pipe weighs in at 2.718 lbs /ft. As far as cross sectional properties the pipe is stiffer due to the diameter and thickness difference. There is a properties call area moment, which is associatied with the cross section. The area moment is a calculated value of a particular cross sections ability to resist bending. For the pipe the are moment is .309 in^4, and the tube is .205 in^4. This means that for a given load the pipe will have lower stress than the tube. The tube is often higher strength, but the extra size in the pipe makes up for much of the difference. For instance a tube that is AISI 1026 hot rolled has a tensile strength of 70000 and a yield of 47000, and A500 tubing has an ultimate of 62000 and a yield of 46000. In a 1020 ERW tube the ultimate and yeild are actually less than the A500 structural. The point is, even if you buy tube, unless you know the spec and the properties you could end up with something not as strong as some pipe. The A53E/B pipe has a tensile of 60000 and a yield of 35000. No that is not as strong as some tube, but I guarantee that in home built cages even with pipe the materials are not the weak link, it will be the welds. I design pressure vessels for refineries and the power industry and we use huge safety factors to compensate for human error. For most of us, our Jeeps are for recreational use. We are not building cages for stock cars. Based on welding ability and design the cages we build from pipe are fine. I have seen a lot of home built cages, some from materials of questionable origin, and in a rollover they are always better than nothing! Sure the expensive tube is stronger, are your welds? The biggest benefit I see in tube is the light weight. I am not saying that people should not build cages from tube, but I am saying that there is an option that does not cost quite as much. As with any personal protection device you need to exercise common sense and not exceed your knowledge or abilities. I am not advocating the following practice, because I think it is wrong, but I have seen roll bars builts with threaded pipe and pipe fittings that have held up in rollovers. I think it would be utterly foolish to build a cage this way, but it is better than nothing. If you are building a cage and you are not a hard core desert racer looking for the ultimate in strength and light weight, I would use ASTM A500 ERW tubing. I am already using it for a cage in my old truck. If you are concerned about weight, spend the extra cash and get the tube. I will probably use the tube in my CJ2, just because the L-head will already have a hard enough time hauling my butt around, if I can save 100 lbs, I will do it.

Cage Up, Wheels Down
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post #8 of (permalink) Old 02-13-2002, 08:38 PM Thread Starter
 
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Re: Roll Cage

Bob, let me rephrase what I said.
When I purchased the tubing the salesman said it was the same thickness as schedule 40, or 3/16 of an inch.
He also said it was the type tubing the majority of the dirt track racers in the area use.
I figure it will hold up to my 2800 # vehicle.
Thanks for your concern though.



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post #9 of (permalink) Old 02-13-2002, 09:44 PM Thread Starter
 
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Update on Roll Cage

Well, I got the front hoop bent today.
This took a while longer since it has eight bends in it as opposed to the two bends the rear hoop has.
Also, I made sure to measrue everything five or six times before marking and bending it.
It turns out that it paid off to do this.
The front hoop is the same width as the windshield, follows the contour of the windshield and dash, and then goes to the floor from there.
Tomorrow I think I will try to weld the foot plates on, drill the necessary holes in the floor, and bolt both of them down so I can take some measurements for the spreader bars, and the rear support pieces.
I don't know if you guys are interested in this at all, but I thought I would keep you posted anyway.
Take Care.



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post #10 of (permalink) Old 02-13-2002, 10:15 PM
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Re: Roll Cage

i've been doing over kill. i've made nerf bars out of sch 80 and i've sliped sideways a couple of times and came down hard and that 2" sch.pipe hasn't waivered a bit. thinking about adding on to my cage with it gonna use 1.5 pipe though o.d. is 1.9+ so it will match the tubing better

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