Roll cage design theory

[TurboShortBus]

I was gawking at a Brazilian or Argentinian (can't remember, but I think it was Brazilian) Ford touring car at the PRI show this weekend. The cage was pretty different, and wasn't what I was used to looking at. I'm just wondering how the strength of this design differs from the usual design of prebent hoops and halo bars.

 

There wasn't a single bent bar in the entire cage. Starting with the hoop, it was 3 pieces...2 verticals and 1 horizontal. No tubing corners were mitered, but they were notched. The top ends of the verticals were notched, and were welded to the bottom side of the horizontal. The front bar that runs across the top of the windshield was also a straight piece, with a horizontal bar on each side that tied it back to the upper corners of the hoop. The A-pillar bars went down on an angle, until they met the dash crossbar. At that intersection, 2 more unbent bars (1 on each side) went straight down to the floorpan. The rear kicker bars were just a typical design. The X bars in the hoop were typical as well. As for cage side bars, there was a bar on each side that went from the top corner of the hoop down to where the lower A-pillar bars met the floorpan. Another bar went from where the hoop meets the floorpan to the midpoint of the A-pillar bar where the dash crossbar cuts across. There were a few other random bars here and there that I can't remember right now. All of these intersections were triangulated somehow, so there seemed to be plenty of bracing. Taking good photos wasn't really possible, since all windows were Lexan and they weren't all that clear, and I thought it would be rude to yank the doors open.

 

This is the only time that I have seen a cage that wasn't constructed with the typical bent 1-piece hoop tube, 1-piece halo tube, etc. It's not like it was on a trailer park El Camino, so there must be something to it. Unless, of course, it was just some junk slapped together for a show car.

 

But, if that whole show car thing isn't the case, then is this design any better or worse than a typical cage with a bent, 1-piece hoop bar and a similar halo bar?

 

Mark

[Al F.]

Bending tubes is far more predictable, controlable, and (in the end) less expensive than all that cutting/fitting/welding. I could understand if we were dealing with a material that could not be cold formed, but we're not. Sounds like they either couldnt afford a bender, or wanted to make a fashion statement. Either way, for our application anyway, bending is preferred.

[y5e06]

I viewed some interesting variations here

http://e30m3performance.com/tech_articles/cage_symposium/misc/misc1.htm

http://e30m3performance.com/tech_articles/cage_symposium/cage_symposium.htm

[TurboShortBus]

I viewed some interesting variations here

http://e30m3performance.com/tech_articles/cage_symposium/misc/misc1.htm

http://e30m3performance.com/tech_articles/cage_symposium/cage_symposium.htm

 

Wow, those are great links! Thanks for posting them.

 

Mark

[HMark]

Bending tubes is far more predictable, controlable, and (in the end) less expensive than all that cutting/fitting/welding. I could understand if we were dealing with a material that could not be cold formed, but we're not. Sounds like they either couldnt afford a bender, or wanted to make a fashion statement. Either way, for our application anyway, bending is preferred.

 

Actually, bent tubes have been going out of fashion for quite a while (except in NASCAR). Bent tubes are just springs, not proper, and predictable load bearing members.

 

Off road, rally and professional road racing chassis left the bent tube behind many years ago (they still use bends, but not in the way the NASA CCR requires you to use them).

 

-Don

 

Laying out my cage and wondering why...

[b_tone]

Bending tubes is far more predictable, controlable, and (in the end) less expensive than all that cutting/fitting/welding. I could understand if we were dealing with a material that could not be cold formed, but we're not. Sounds like they either couldnt afford a bender, or wanted to make a fashion statement. Either way, for our application anyway, bending is preferred.

 

Actually if the cage is designed in CAD/CAM and you have access to a CNC laser cutter cut tubes are cheap easy and 100% repeatable. After that it's simply a matter of welding everything together.

 

Using that type of system has been used in BTCC, DTM and the Japanese GT300/500 class with a high degree of success.

[NickS]

Actually if the cage is designed in CAD/CAM and you have access to a CNC laser cutter cut tubes are cheap easy and 100% repeatable. After that it's simply a matter of welding everything together.

 

Using that type of system has been used in BTCC, DTM and the Japanese GT300/500 class with a high degree of success.

 

Those are some *MIGHTY* big and expensive IFs there, sir!

 

 

-- Nick

[TurboShortBus]

Actually if the cage is designed in CAD/CAM and you have access to a CNC laser cutter cut tubes are cheap easy and 100% repeatable. After that it's simply a matter of welding everything together.

 

Using that type of system has been used in BTCC, DTM and the Japanese GT300/500 class with a high degree of success.

 

Those are some *MIGHTY* big and expensive IFs there, sir!

 

 

-- Nick

 

It's only a matter of time before Harbor Freight starts selling CNC machines...lol

 

Mark

[ddteman1548534717]

When you are discussing roll cage design it's always good to remember what you are designing it for. It can all go wrong in a hurry. Any of these could happen to any of us in our cars. There is no such thing as too much roll cage.

 

http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=1538829

This Mid Ohio where we run our Championship.

 

http://video.google.com/videoplay?docid=-265805483990438725&q=car+flip&total=2373&start=0&num=10&so=0&type=search&plindex=1

 

http://video.google.com/videoplay?docid=-6012611374785580896&q=porsche+crash&total=1274&start=0&num=10&so=0&type=search&plindex=5

 

http://video.google.com/videoplay?docid=-4964736131704437645&q=porsche+crash&total=1391&start=10&num=10&so=0&type=search&plindex=6

 

http://video.google.com/videoplay?docid=-5268446070883827727&q=massive+V8&total=62&start=0&num=10&so=0&type=search&plindex=3

 

The worst case.

Edited December 13, 2007 by Guest

[Lady in Nomex]

Definitely no such thing as too much roll cage! Thanks to this cage built by Alan Blaine at Blaine Fabrication I was able to save this car:

 

 

From this:

 

 

To this:

 

Note the doors shut fine after the crash - there was not even a bend in the floor pan nor scratch on me!

 

[Al F.]

Steel tubes have been going out of fashion for a while. Just have a look at a modern F1 car!

 

NASA cage rules are written for a different audience; small shops and back yard mechanics. The probability of the cage builder of a CMC car having the kind of equipment and experience required to get to the point where cutting/fitting/welding is more predictable than bending is laughably small.

 

I'll agree I was too harsh saying the original car in question was built by someone wanting to make a fashion statement, but I stand by my statement that for our application (small budget, ammateur built) bending is the way to go.

[ddteman1548534717]

This is what I came up with for my 94 Mustang. Copied the design from a WRC Ford focus.

 

[TurboShortBus]

This is what I came up with for my 94 Mustang. Copied the design from a WRC Ford focus.

 

How did you take care of the welds at the top of the hoop, etc. where they are close to the underside of the roof? Cut the top off and weld it back on later, or holesaw the floorpan and drop the cage out the bottom? Or another method?

 

Mark

[ddteman1548534717]

The cage is mounted on the rockers which sit about 4" off the floor. So it was tacked lowered then welded and raised back into place. It's not finished yet but it's a good start.

[FBody383]

The cage is mounted on the rockers which sit about 4" off the floor.

 

Would you mind posting a couple pics of those?

[ddteman1548534717]

 

[NickS]

For whatever its worth, here are some pics of the cage that Alan Blaine put in the Red Car:

 

[TurboShortBus]

Hey Nick...any idea which Millermatic welder that is in the 4th pic down?

 

Mark

[NickS]

Looks like a Millermatic 175 based on the full size image:

 

http://gallery.noid.org/gallery/album07/door_bars_1?full=1

[TurboShortBus]

Looks like a Millermatic 175 based on the full size image:

 

http://gallery.noid.org/gallery/album07/door_bars_1?full=1

 

Yup, that would do it!

 

I have a Millermatic 140AS that I bought at PRI last year. That AutoSet feature is pretty cool. I actually have to try to screw up a bead now. I still need to get motivated and finish hooking up the 230V panel for my Millermatic 351 Syncrowave TIG that I bought a few years ago...then, learn how to use it properly.

 

Mark

[NickS]

I just have a little hobart 125A that my wife bought as a birthday present 18 months ago. Now that the workshop is finished I finally busted it out of the box a few weeks ago and started playing around withit. I've never welded before nor taken any classes. Brad Simpson stopped by and gave mea few pointers and lent me his spare helmet. I've been trying to find excuses to weld things now

 

A bigger mig and a tig are definintely in my future

[TurboShortBus]

I started out with a $200 Craftsman "gas-less MIG" (aka wire-feed flux core junk) about 7 years ago. That lasted a few weeks before I returned it and got a $300 Craftsman MIG (made by Century) and a tank. I used that up until about a year ago to do exhaust work and other little things that didn't need to be too pretty or structural, until I picked up this Millermatic 140AS from a local vendor at PRI. Wow, this sucker is worlds better than that Craftsman/Century heap, for sure. Even writing my name on an old muffler with it was much smoother and cleaner.

 

Mark

[Al F.]

My Miller "hot glue gun" is the handiest tool in my garage. Don't know where I'd be without it. Next is a version that can travel to the track!!

[supermac]

My Miller "hot glue gun" is the handiest tool in my garage. Don't know where I'd be without it. Next is a version that can travel to the track!!

Why would you want to bring it to the track Al? Did you buy a Mustang?

[NickS]

No, I heard that the gophers in Texas are building armored walls around their dens to protect themselves from Al. He's probably going to need the welder to fix the car after he has a run in with one

 

-- N