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hrew safe??

3K views 34 replies 12 participants last post by  RRich 
#1 ·
I was down at the racecar shop near me looking for Dom tubing. The mechanic who builds their chassis told me that they use all hrew tube in for their chasis. Just wondering if it is tough enough to obsorb the crashes they are involved in would it work in a Jeep? I was thinking 120 wall. He did say that you had to plan your bends carefully around the seam.
 
#3 ·
[ QUOTE ]
if its a trailer queen then its all good

[/ QUOTE ]

If it's a trailer queen then why not save some money and go with Sched 40 ABS...would cut out the need for a bender...just grab some fittings at your local plumbing supply...and it's much lighter than any metal pipe...
 
#6 ·
before someone starts ranting......

HREW is a tube...so it has tube dimensions, but is seam welded like pipe.
these are OK for a cage IF
1)you use the correct grade structural steel (not cheapy stuff)
2)you are not having a hgih speed roll situation like racing

IF both of these are not met, THEN you will have problems, and should use DOM tubing.

soo...no digging up old posts, i think Jeff knows not to use old cast sewer pipes as a roll cage.
 
#7 ·
[ QUOTE ]
you are not having a hgih speed roll situation like racing

[/ QUOTE ]

So then how is it that the race shop who has to pas inspection on their cars and build them to the standars of the sanctioning body use it??
 
#9 ·
[ QUOTE ]
[ QUOTE ]
you are not having a hgih speed roll situation like racing

[/ QUOTE ]

So then how is it that the race shop who has to pas inspection on their cars and build them to the standars of the sanctioning body use it??

[/ QUOTE ]

The answer is simple. The race cars often build internal cages and frames that are engineered to sustain the forces required to keep the driver as safe as possible at those speeds.

Jeeps are much heavier and can roll at 70MPH on a freeway, or 4MPH on the side of a 40* hill. Now sit down and engineer a cage/frame that will sustain the forces necessary to keep you and your passengers safe in both conditions. I think you'll find that DOM will be a heck of a lot safer.

So, what ever you use, you're betting your life on...

For my life, and that of my family... I'll take DOM and never look back.
 
#10 ·
Ok, I went to the SCCA website and viewed the pdf of the 2005 rules. I can't post a page, as its an 11mb pdf file SCCA Page to download the rules . See GCR Section 18. They allow chromoly, dom, seamless and ERW tubing for cages. They specify minimum diameters and wall thicknesses for each material. For ERW it is a minimum of 120 wall thickness and they specify various diameters and wall thicknesses up to 180 wall depending on the weight of the car (some over 4000 lbs). I would think if its good enough for race cars, it would be good enough for a jeep. It seems to me you need to pick the right diameter and thickness of ERW for the job.
 
#12 ·
DOM still has a seam, it's just pulled and twisted into a spiral. Like that you cannot put the seam on the inside unless you are making a corkscrew cage.
Seamless DOM is very rare, and VERY expensive.

DOM is work hardened from the pulling process. It's harder to bend and is more likely to shatter.

Since DOM is harder, when you weld it the area around the weld softens to just about like ERW would be after welding - giving it nice fracture points due to the greater difference in hardness after the welds. The heating process of the work hardened material causes Markesite - essentially crystallization.

But -- since it's more accurate in wall thickness and diameters, you can use it for hydraulic cylinders - what it was initially designed for.

Do web searching for suppliers, history, applications, how it's made, and how to use it properly. You'll find it very interesting.

Proper design and an extra brace here and there, gussetting, and internal stubbing will gain far more strength than trying to use exotic materiels.
 
#17 ·
dom= drawn over mandrel
hrew=hot rolled, elctro welded (Or something to that effect)

It's my understanding, Jeff, that DOM is just hrew that has been rolled to smooth the seam and hold tighter size tolerances. The hardening effect of this process that RRich mentioned is an interesting point, though. And also as Rich mentioned, truely seamless tube is, for all intents and purposes, out of the picture.
Buy that bender yet, ol' buddy?
 
#18 ·
Here's a small bit of the UROC Rules for 2005.

4.12. Roll bars/Cages
4.12.1. Definition: UROC considers the cage as the safety bars surrounding the occupants. Designed to protect the
occupants in the vent of a rollover.
4.12.2. A six (6) point mounting cage that protects all seats in a vehicle is required.
4.12.3. Basic roll cage must be constructed of material meeting or exceeding the following minimums:
4.12.3.1. Round magnetic steel (1026 DOM recommended) tubing 1.50" OD with 0.120" minimum wall.
4.12.3.2. Chromoly alloy steel A 519 grade 4130 1.50" OD with .090 minimum wall.
4.12.3.2.1. Must be quenched.
4.12.3.2.2. Normalized is not approved.
4.12.3.3. Roll cages made of other material or in other wall thickness/diameters must be done through an UROC
approved builder and have a certification and serial number on file with UROC. Roll cages already built of
other material or specifications than those above must be inspected and approved by UROC and there may
be a fee for this inspection. Contact UROC for information.
4.12.4. Any other materials are not permitted (aluminum, composite, etc.)

All UROC Rules are availiable online.


Dale
 
#20 ·
That's what I was wondering too.

I have been told that everything built at Badlands Machine Shop for a UROC competitor is DOM. I asked the question last time this came up, they don't want to take unnecessary risk. Also will "test" and often damage the cage two or three times a season. I noticed some added bars during last season.

It has been said that the design is much more important than the material. Guess it takes both to go out and not be worried about a flop when you push it that hard.

Here's some interesting strength info , just something I stumbled across.

So what is the difference in price?


Dale
 
#21 ·
So according to UROC a formula car would not qualify for a roll over, but they can withstand a 200 MPH crash?

No space frames, no monocouqe construction either.

Do they allow rubber tires yet or are they still requiring Fred Flintstone's stone tires?

Only a few years ago thier rules required a minimum of a 4 point 3" tube. Water pipe vwas acceptable if it was Sched 60.
Now they'll accept 1.5" tube?
Times are a changin.

Try something - get a hunk of DOM - notice the spiral - that's how you ID it. That's the seam twisted in the process.
Now bend it sharp.
Bend the ERW the same.
Put both pieces in a press - smash them.
Search the internet for info - Yahoo, Google etc - not here.

You decide what you want protecting your bucket.

I did, and made my decision.
 
#22 ·
[ QUOTE ]
Since DOM is harder, when you weld it the area around the weld softens to just about like ERW would be after welding - giving it nice fracture points due to the greater difference in hardness after the welds. The heating process of the work hardened material causes Markesite - essentially crystallization.

Proper design and an extra brace here and there, gussetting, and internal stubbing will gain far more strength than trying to use exotic materiels.

[/ QUOTE ]

So,,, is this to say that the welder of your cage needs to take special measures to prevent the "Markesite - essentially crystallization" - regardless whether DOM or ERW? If so, does that mean a cage oughta be TIG'd together, and least desireable is arc welding? (I'm in the learner stage in both the welding and cage construction areas.)
 
#23 ·
I can get hrew for about 2.80 foot, for 1 3/4 I priced 1 1/4 dom and it was 7 something a foot and those prices are for a length.

I realize that you want the best possible protection, I do however know that there is a point at which "beef" for lack of a better word, fails to gain you anything and in some instances actualy hurts you. I have seen a huge push to over build items. Our bumpers are a good example built tougher than anything they attach to, but that is what the market dictates. I am just wondering if the market now simply dictats DOM and that is what the cool kids are using. I have no doubt that the strength is greater. I am just wondering how much is enough. I hear people brag about the Moore cage, and from what I can tell it is hrew and by their own admission not intended for offroad use (gotta please those lawyers).......
 
#24 ·
I did a search for "roll cage design" and here are a few things that I found interesting:

From Safety Devices Company in U.K.:

Cages may be made from either Cold Drawn Seamless (CDS) tubing, or the more malleable Electrically Resistance Welded (ERW) tubing. The latter shows a cost saving, although it is not generally permitted for motor sport use.

From NHRA:

A roll bar is required in any convertible running 13.99 seconds or quicker in the quarter mile, and in other cars beginning at 11.99. The roll bar is accepted in vehicles running as quick as 10.00 second e.t., provided the stock firewall and floorboard is intact, other than for installation of wheel tubs. The rollbar must be constructed of minimum 1 ¾ inch o.d. x .118 inch wall mild steel tubing, or 1 ¾ x .083 chrome moly tubing, and must conform to the following diagram:

Another from NHRA:

As stated in the NHRA Rulebook under SFI Spec 2.7A, "A helmet guard of 1x.058-inch tubing must be installed all the way around the roll cage at a height approximately halfway between the top of the roll cage and the shoulder hoop(s), but not to obstruct vision. This is required for both five- and six-point roll cages."

From Open Road Racing:

Roll Cage Specifications

From WSCC:

The main hoops and primary bracing should be constructed from round, mild steel, ERW or DOM type tubing. Chrome molly tubing such as 4130, may be used but is not recommended.

From Pikes Peak International Hill Climb:

5.2 Material: The roll cage must be constructed of SAE 4130 steel tubing or 6061-T6 aluminum. The roll cage material shall be the same as the material used in the frame (steel or aluminum). It will be the responsibility of the vehicle owner to provide documentation as to the specifications of the material used if requested. The roll cage must be gusseted in all four corners. It is recommended that all gussets be made of seamless tubing thereby eliminating any sharp edges which might endanger the competitor in the event of a roll-over. Rear bracing struts are to be incorporated into the construction of the roll cage. For the purpose of determining tubing sizes, the vehicle weight is without competitor. The minimum size of tubing shall be determined as follows:

Score Desert Racing (BBS discussion)"

new roll bar rule?

Here on off-road.com/jeepweb.com:

M.O.R.E. Bolt-In Sport Cage

For some reason that setup scares me, just my opinion, for more on information on that product.
Mountain Off-Road Enterprises

From 4x4wire.com by Terry L. Howe:

For recreational wheeling, I felt that 1.75"x0.120 wall DOM tube would be best for protection and space. The 2" tube takes a lot of room and the 1.5" is kind of small unless you are going to run a lot of cross braces. I've seen and been in rollovers with 1.75" tube and it has held up well, even with cages that are pretty airy and not triangulated very well. I probably could of run a thinner wall tube for the dash bar and rear cross braces, but it was easier just to use all 120 wall. I definitely wanted the 120 wall for the main hoops and upper cross bars since 120 wall resists denting a lot better than thinner tube.

Another 4x4wire.com by Harry Wagner:

Fortunately All-Pro Off Road offers a roll cage kit for Toyota pickups and 4Runners constructed out of 1.5" .120" wall DOM tubing that closely follows the contours of the Toyota cab. It is my opinion that this is the best cage available for Toyota pickups, offering custom fabrication at a mass produced price. The cage comes pre-bent but disassembled, so welding and notching are required.

After a roll over:

Lady's Custom Built Roll Cage

My disclaimers:
1. I don't know poo about roll cage design/construction.

2. I can't weld anything intentionally, bearings sometimes.

3. While I have been known to hang around with UROC folks that is not to say that I truly understood the conversation in the first place.


The intent of my contributions to this thread are based from the fact that I consider Jeff (RioGrande) a friend and wish to keep him as healthy as his own bad habits will allow.



Dale
 
#26 ·
Great info, thanks.

One thing for sure - SOMETHING IS BETTER THAN NOTHING!

Planning on the type of rollover?
You could say a friend of mine had a simple slow speed roll. He was off angle on a side hill, going real slow in his TJ. Left side had to go over a rock, slightly too high, flopped onto it's right side almost in slow motion.
Then onto it's top, the fiberglass made that crunching $$$ sound.
Then onto the other side, still slow and easy.
Then onto it's wheels again - nice. But now the hill's too steep.
Ooops, over again, and again, and again - faster and faster - then he dissapeared into the canyon below!

It was too steep to climb down, had to make a trail down around the end.
Fearing the worst we finally got there.
He and his wife had climbed out. He was sitting on the side - As we drove up he said "anybody got a spare tire I can borrow?"
They were fine. We even drove it out.

ERW? DOM? PVC? Water pipe? No, the stock inadaquate TJ cage worked. Not to say the TJ cage will always save you though. But imagine if they didn't have it at all.

Are you only going on trails where you can flop it just once at low speed?

Proper design, proper welds, correct lenghts are far more important than the slight differences in material strength. I suppose even PVC with the proper design could be used - but???

I like things to be NOT WELD DEPENDANT. Find an old "store bought" or custom bar/cage. Cut through the welded areas - look for proper penetration. It's often scarey what you find. To think someone's life depended on that!

Look at cages after they crashed - see how and where they failed or bent. See what held fine. Ask WHY? Try picturing where a small gussett or brace would have helped. And where the ones that are there did their job. Each situation is different, what worked fine on one collapsed on another.

Good design - Meaning -- stresses pushing the bars together rather than pulling or twisting them apart, loads spread out over long distances, braces not positioned like spears to the occupants in case a weld breaks.

For the welding - I said I don't like things "weld dependant." My belief is that the cage should be mechanically sound - the welds only keep things in position till it's tested.

A technique I almost always use - internal stubbing. It's an internal gusset.

Say for example a "T" or butt joint.
Using 1.75 x .120 tube - cut a 1.5" hole in the top of the Tee (hole saw, not a torch.)
Slide a piece of 1.5 x .120 inside the fishmouthed connecting bar, poke it into the hole. Make sure there are no gaps, that it's a good solid connection. Make sure that internal piece goes in as far as possible - reverse fishmouthing gets it in deep. Extend it into the connecting bar at least twice the connector's diameter.
The inside tube supports that connection from the inside - mechanically it's already stout in most directions without even being welded.

Now when you weld it you can turn the heat up and get really good penetration without burn-through. Instead of welding 1/8 material with light amperage you are welding 2 pieces of 1/8 together - equiv to 1/4". Even it you never penetrate through the full 1/4, for sure you've penetrated the outer 1/8.
Mechanically it's strong, and the welding insures it's going to stay that way.
Sure, it's lots more work.
(And it sure makes it easier to construct the cage - you can usually put it all together without welding, making changes without scrapping welded pieces. Once it meets with your approval, tack it all and then weld away!

I started doing that technique right after I witnessed a rear brace's weld break, the brace slid around the main hoop and went through the seat and the driver's back and out his chest - all the way through and out the front! Ouch!!!!!!
Paramedic helicopter, fantastic life saving guys on it - They cut the brace off and took him in with it still in him.
Believe it or not, HE LIVED!!!!! I can't give enough credit to those flying paramedics!

So I guess my main point is "Thmimk" - and use the best design you can. But do SOMETHING!!!!
 
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