CAMS spec roll cage build

[Sprinkles]

This thread explains how I built a fully welded in CAMS spec roll cage for State Level racing. At times a frustrating exercise, but in the end I’m very satisfied with the results, and saved a few $$. I hope it's helpful for others who want to build their own cage.

[Sprinkles]

The big picture

Before we get into the nitty gritty, I thought it might be useful to summarise my learnings from this exercise. This isn’t the first roll cage I’ve built, but it’s been a very long time since I last built one, the regs have changed a bit, and I’ve forgotten a lot.

Firstly, if you want a cage in a hurry, buy one. As an amateur, building roll cages is time consuming if you want to do a good job.
If you are going to build a cage and you want to minimize the time taken, build it as a bolt in cage rather than weld in. Welding on a bench rather than inside the car is a lot quicker. And design it so the front legs don’t go through the dash, removing the dash and neatly cutting it up to accommodate the front legs adds a fair bit of time.

There’s a lot of time in fitting up the tubing nicely that anyone with some basic skills can do. If you are not up to welding, tack it all together and get a professional to weld it for you. You will still save some money and still be able to call it your cage.
For a fully welded in cage, if you can strip the car down to the shell, put it on a rotisserie and remove the windscreen, the welding is a lot easier as you can get better position. I didn’t to this. Welding upside down with my head jammed between the sill and the side intrusion bar was not the highlight of this project.

Probably the most important part of the whole exercise – Read and re-read Schedule J of the CAMS manual, and make sure you completely understand what you are building. If in doubt, phone CAMS, they are super helpful. It’s also worth looking at some race cars in the pits in the category you are considering racing in, to see how Schedule J is implemented in practice.

[Sprinkles]

Tools

You could realistically build a roll cage with an angle grinder, a half round bastard file and a welder.
However, the following make the build quicker and easier:

• Two angle grinders, a 5” with a cutting disc, a 4” with a flap disc
• 200mm digital protractor
• Digital level
• Milling machine with a tilting head (drill press as an alternative)

[Sprinkles]

Design

The first thing you need to figure out is what level of competition you are building your cage for – supersprints, state level racing, or national level racing. The requirements are different, and basically the higher the level of competition, the more involved the cage build. I built this cage for state level, but allowing for an easy conversion to national level.

The basic shape of the cage is the main hoop and front legs. I was advised to mock up the shape of each out of timber and exhaust tubing respectively.

The curved ply is the same radius as the mandrel bends of the main hoop, 6.5”.






The exhaust tubing is slit then bent to shape, fitted up and tacked.

[Sprinkles]

Tube bending

Rod at Andrews Race Cars supplied and bent the tubing, at a very reasonable cost. His main business is tubing supply, not bending and fab, so if you want him to do your bending, you need to be patient. Having said that, it was worth the wait, as his bends were perfectly matched to my templates. Rod also supplied a handy guide for installation.

Here’s what I got back:




If I thought I was going to build a couple more cages, I would spend a K on a proper bender and dies, and have a go at doing the bending myself.

[Sprinkles]

Getting the build under way

It's really important to get a tight fitup, as this affects the quality of the weld. I read somewhere that any gap should be no more than the thickness of the filler rod you are using (this cage is TIG welded), so in my case 1.6mm maximum.

There's some good videos on Youtube on how to fishmouth tube by hand, I did a mixture of hand and machine.

The centre out of a roll of kitchen paper fits perfectly over the tubing, and can be used to precisely mark out the position of fishmouths.




A bicycle workstand is pretty handy for holding the front legs







And the result: A pretty good fitup, not yet bevelled at this point.

[Sprinkles]

Using a hole saw in the milling machine is another way to do fish mouths. It's good if you want to do multiple at the same angle, but I can do a single fishmouth with two angle grinders just as quick and accurate as the mill.

And get yourself some v blocks to hold the tubing on the mill bed before you start the project, not half way though like I did.






That's the front roof brace fitted up:




The tilting head on the mill is also useful for cutting specific angles







An important rule to remember is that your braces need to finish within 100mm of the mounting foot:




And that's the main hoop diagonal fitted up:

[Sprinkles]

The next thing to fit up is the so-called taxi bar, or harness bar.

I wanted it to be exactly parallel to the top of the main hoop, and it's in two pieces. I flailed around for a while with this sort of nonsense:




Then I remembered Project Binky:







End result looks pretty good to my eye

[Sprinkles]

First mistake

So i installed the seat only to discover the first mistake:




The harness bar is too high, which would result in the harness going onto the driver's shoulders at the wrong angle.


Oh well..... it's always quicker the second time you do the same job.....

[Sprinkles]

Welding on top of the main hoop

You need to give some thought to how you are going to weld the entire way around the joints that are up against the roof. There's a few different ways of doing this, you can cut holes in the floor and drop the cage down, you can cut holes in the roof (not recommended.... ask me how I know), or you can build pedestals underneath the legs, or you can use a pre-existing pedestal. I did a combination of the last two methods, as I wanted to minimise cutting up the body shell.

The main hoop was positioned on the step under where the rear seat used to mount. So I just hand to slide the hoop and front legs forward and it would drop down enough to get the welding torch onto the top of the main hoop.





For the front legs, I made pedestals. These were my first attempt, and my second mistake of the build. Mounting plates need to have 120 square centimeters in contact with the body shell, and this first attempt didn't even come close. I've seen a number of cars that don't comply with this rule, not sure if scrutineers don't properly understand this, or if they just turn a blind eye.




Here's the second attempt, which complies with the rule:

[Sprinkles]

Time to mock up the basic cage:




Bunnings ratchet straps and ockies are good to hold everything in place before starting tacking it together.

[Sprinkles]

So then I decided to add some enhancements, triangulating the main hoop and front legs, and adding a roof diagonal, which is required for a national level cage. Windscreen supports are also required, but these can be easily added if the car ever looks like getting to race at a national level race. Retrofitting a roof diagonal would be a PITA.

By now I had got some v blocks for the mill, these make life a lot easier




And here's how you set the angle of the mill head precisely. Put a bit of straight rod in the chuck, then measure it with the digital protractor relative to the mill bed:

[Sprinkles]

Welding

At some point in the project I decided that I would weld the cage myself. This required hours of practice on my TIG to make sure my welding was good enough.

One of my many practice pieces, that were cut open to verify full weld penetration, and bashed with a sledgehammer to make sure the welds would no crack:




The first welding was the main hoop, done on a bench. Problem was the driver's side of the main hoop pulled in from the heat where the harness bar was welded, this needed to be straightened when the main hoop was welded in.







The front pedestals were very awkward to weld on the firewall side











And another learning experience: If you don't thoroughly clean the sound deadener of the underside of where you are welding, here's what happens:



If you had both a MIG and a TIG, I suggest welding around the foot plates with the MIG instead of the TIG, as MIG is a lot faster. You do see plenty of cages welded with a MIG, however, it was explained to me that you risk not getting full penetration in the areas where welds are restarted on tubing.

[Greg Rust]

Great thread. I bought a 6point kit from Andrews Race cars and it was a brilliant starting point for my cage.

[Slides]

Thanks for sharing