Rollcage

[kristafa]

Here is my first attempt at installing a rollcage into my BMW. Upto this point (with the front not welded yet) I've spent about 6 hours on the cage, side instrusion bars are yet to be installed, ran out of tig rods

The cage is bolted to the floor (as per QLD DOT guidelines) then barwork is welded in. All our bending is done manually with the help of the awesome JD Squared tube bender. Notches are done with a grinder using the 'chop saw method' which gives a great welding area with minimal gaps to fill.

All joins are tig welded.

Thanks to my mates for their assistance.

Some parts of the cage are like that by design, other parts are out of necessity, i know alot of people have their own ideas on cage design, but for my purpose (weekend track work) this should be sufficient. I've got about 100mm of clearance between my head and the overhead section of the A pillar bar, would like this to be a little wider but was limited to where i can get a good weld with the tig, and i wanted to triangulate the rear backstay bars and this A pillar section for strength.

thanks for looking!

pics..

the mighty tube bender!!! \/

cage pics \/

[GUN_METAL_GTR32]

awesome work kris.

are u going to be painting the cage and the interior of the car ? what color??

[warps]

Looking good.

Good to see someone else using the drop saw mitre technique for prepping ends. No need for expensive notchers (I don't know why everyone always goes on and on about them). Are you using CDS tubing? (looks like it in the photos) How does the pipe bender handle it? Reason I ask that my cage fabricator stopped making cages when they brought in the compulsory use of CDS tubing, becasue his pipe bender couldn't handle it anymore. Then again, he ran an exhaust shop, so probably only used light bending gear designed for exhaust pipe. Annoyed me big time, becasue he used to make a great quality cage very cheap.

Mind you; the market is different now, and there are literally dozens of options for getting cages made, so prices have come down a lot from 10 - 15 years ago.

[kristafa]

Yes its CDS, I pay around $20/m for it, its 1.75" x 2.6mm. my mate who is about 5" tall and scrawny (sorry aza, but you are) is able to bend tube like the incredible hulk on that bender!

cage will be painted in 2pack gloss like the exterior

[Risking]

Is this you first cage?

Why did you do the a pillar top runner like that?? Im assuming so you could get a full weld. If you use the right methods you can drop the hoop and get a nice weld on it whilst keeping the tube tight to the pillar.

Also if you plan to do another use small sections and half jig the main hoop. Doing this you can get a perfect fit thats tight to the pillar and the roof without having to guess from measurements and angle guages. You will "waste" a meter of so of tube but if you use sections, bend then tack them together to make half the hoop it works perfectly and you can bend the whole thing knowing its a "tap" in fit.

These are typical fits done by jigging the hoop the first time around, takes about 10 mins to quickly make a mock up jig.

http://www.skylinesaustralia.com/forums/up...4009_100635.jpg

http://www.skylinesaustralia.com/forums/up..._4009_46120.jpg

Who band CDW tubing?? Ive complied/ built plenty of cages this year gone by in CDW with CAMS

christo if you plan to do another and need material I keep a massive amount of CDS, CDW and 4130 in stock, I can probably kill the $20/m your paying now including the shipping up there from Sydney.

[kristafa]

yes brad its my first cage (those who have built many will no doubt find flaws in my design). I heard CDW actually has a higher strength rating than CDS, i think i read this in the cams manual? 250MPA vs 350MPA??

The cages in your links look great, hope to some day get a result like that!

[VB-]

risking, what technique do you use to get at the top of the cage? helped a mate do one not long ago, didnt want to hole-saw out the floors so we ended up using some heavy angle to box up where the main hoop meets the floor. tacked all the cage bits together then pulled the whole lot forward till it dropped down off the 'box'. how do you go about it?

[Risking]

The minimum is 350mpa.there is a few different sizes you can use.

I haven't heard of CAMS banning CDW though.

The FIA rather CDS but as far as I was ever aware still acept CDW if the cage is built to a CAMS homologated design.

Ben I use a few different ways depending on the car. The most common is to fit the hoop onto the rear seat step. That allows the hoop and legs to come forwards an inch and drop down 4-6 inchs normally. It also makes the hoop shorter.

Another way is to hole saw the floor, use an triangle box section in the corner but make an upper and a lower plate. The upper plate gets a 1 3/4 inch hole in it for the hoop to pass through. The bottom plate gets welded over the floor hole, the hoop gets welded to the base plate then the upper plate gets lowered down and welded into the corner as well. The triangle section gets boxed in and done.

A few things it covers the hole you made in the floor neatly, doubles the hoops mounting point, gives an extra strong jacking point, and it's neat.

I do all my 4130 cages this way as I've never had a problem getting homologation and if your doing that kind of cage you can afford the extra time to do it.

The small gap between the lower plate and the floor I fill with rust preventor and expands foam. 10 years plus and not a problem.

If your TIG welding the cage you can buy really nice small torches that use a much shorter tungsten or one broken in half. It frees up alot of room when welding, or buy a small bung for the rear of the torch instead of the long ends they usually have.

Tube notchers are the best way to do it too. String line the bar you want to put in, use a sliding bevel and get the angle. Transfer that angle onto the notcher ( mine will do up to 70 degrees) set up the tube and use the perfect size holesaw to make the notch. It's perfectly accurate and if there is even a .5mm gap your doing something wrong.

Speed werx in nsw make a brilliant notcher and it's pretty cheap.

The drop saw method works but if you want perfect joins then it takes some time to get right with a grinder and linisher after cutting.

I just make the cut then run the outside around the linisher to take off the edge. It fits perfectly and the weld will be consistant with the same ammount of filler the whole circumference.

[warps]

Risking,

I've just been going from my memory from when CAMS changed the roll cage regs back in 2000-ish (can't recall exact date). At the time, I'm pretty sure that the welded pipe was only 250MPa, so "not up to the task" accordig to CAMS. As a result, CDS was the go. I wasn't sure whether they didn't like the lower yield strength, or the seam in the welded pipe being a weak point / stress raiser, hence CDS becoming the tube of choice.

I don't actually have any proof that welded pipe is unacceptable, and as you say it may be perfectly fine. In fact, "mild steel" sections these days generally refer to 350MPa steel, so based on that, the standard tubing is probably OK. Funnily enough I have a bit to do with steel tubing through work (mainly 4" - 16" diameter on dragline booms) but have never given the cages much of a thought. The specs we deal with on dragline booms prohibit the use of welded pipe, yet when the OEM sent us some replacement welded lacings, they quickly back tracked and said they'd be OK to use in our particular application, but not anywhere else. Yeah yeah.

Edit: Do you go for a root gap when you join the pipes, or do you butt the pieces up against each other? I guess that the thin wall means that shrinkage of joints isn't much of a problem, so no gap needed.

Edited November 30, 2010 by warps

[VB-]

Ben I use a few different ways depending on the car. The most common is to fit the hoop onto the rear seat step. That allows the hoop and legs to come forwards an inch and drop down 4-6 inchs normally. It also makes the hoop shorter.

Another way is to hole saw the floor, use an triangle box section in the corner but make an upper and a lower plate. The upper plate gets a 1 3/4 inch hole in it for the hoop to pass through. The bottom plate gets welded over the floor hole, the hoop gets welded to the base plate then the upper plate gets lowered down and welded into the corner as well. The triangle section gets boxed in and done.

A few things it covers the hole you made in the floor neatly, doubles the hoops mounting point, gives an extra strong jacking point, and it's neat.

thanks heaps for that Brad. wouldnt that leave to main hoop too far back though? not sure on the exact regs, just see most people put them close to the B pillar as poosible (or is that just to hide it?).

if you've got any more pics of how you do the base plates, or just a general walkthrough of the process of building a cage, throw em up too

[Risking]

The b pillar is usually wide enough to still hide the hoop. The hoop is usually as close a possible to the pillar to keep the strength.

The regs state that the hoop must not overhang the drivers helmet but be within 100mm.

A while ago I did a run through about building a cage in a 180sx. It started okay but from memory it turned to shit when a million interweb experts who have never built more than one or two cages started to add their two cents about how there was better ways to build and design a cage.

I in way know everything and am always open to listening to other peoples methods, I've used them on the odd occasion too but I gave up.

[VB-]

ahh i see, i vaguely rememeber that thread, thanks heaps anyway

[Risking]

Next time I do a cage (next week) I'll take photos of the process I use to get a good tight hoop and legs. I don't mind sharing the knowledge where it's appreciated.

[VB-]

yeah mad, i'm keen on doing one on something, havent decided what yet, have access to all the steel and a hydraulic bender (i'm a supposed to be a boilermaker lol)

last one i mentioned was pre-bent kit from mac bro's racing, we just welded it in, on that note it was f*cking terrible too, although i've heard good things about them, i found the kit to need alot of work before it went into the car. was very expensive tube with some bends in it

[Risking]

That's the problem with the current pre bent cages around. Despite the manufacturers weld in cages being great quality their kit cages are very average.

Have you seen my cage thread in the motorsport section? I'm working on some neat fitting bolt in and weld in kits.

How did the rest of your BMW cage turn out??

[VB-]

i'm off to the motorsport section now to sus it out

[kristafa]

my bmw cage?? well its all painted now