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How to weld a Roll Cage


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#1 lordmulgath

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Posted 22 March 2011 - 06:22 AM

Saw this over on jalopnik and figured it would be good info for the forum:

For the original Link click here


A roll cage is a specially-constructed tubular frame built in or around the cab of a vehicle to protect its occupants from injury in the case of an accident or rollover. A standard feature in race cars and stunt cars, roll cages are made of steel tubing and include a geometric design to enhance stability and strength. "Beware the first time roll cage builder," warns Dennis McCarthy, a veteran Hollywood stunt and race car builder whose car coordinator credits include The Fast and the Furious, The Green Hornet and Batman Begins. "Always consult with someone who knows what they're doing. And hopefully you'll never have to test your work, he says.

"A simple four-point cage can be done in a day," McCarthy says. An extensive stunt car cage can take up to a week. (These times assume some skill in welding and tube cutting.)

Tools:
- 1 3/4-inch tubing
- Tube bender
- Tube notcher
- Tape measure
- Metal pipe cutter
- Brace
- Hand grinder
- Protractor or carpenter's angle finder
- MIG or TIG welder

Step-By-Step:

1. Make Room
You need to remove the seats and carpet from the vehicle. Carpets and seats get in the way and pose a fire hazard. You may choose to remove the headliner as well, but it is nearly impossible to replace it after you've installed the roll bar.

2. Size Up the Ride
Measure the interior dimensions of the vehicle to determine the size of the roll bar you're going to need. You'll need to know the height from the base plate or frame rail to the headliner. Then, measure the width of the hoop at the top and between the base plate or frame rails. "This is also where you will need to determine the diameter and wall thickness of the material you are going to use," McCarthy says. "This is based on the use, size and weight of your vehicle." Builders frequently consult contest rule books for cars to be used in competition.

3. Take Rough Measurements for Your Supporting Bars
These are generally straight pieces. Wait until the main hoop is in place to get the exact lengths, but you can get a rough estimate of your total tubing needs before you bend or install any tube. Once the main hoop is in place, re-measure, cut and install the supporting bars.

4. Calculate the Bends
Once you've done the measurements above, you know the length of tube you need for the main hoop, where the bends should go, and how much extra tube you need for supporting braces. Now you can buy your tube and have the main hoop bent to your specifications. Cutting the arms a little long is better than a little short.

5. Set the Base Plates
You want to use large base plates (generally 36 square inches and 1/8-inch thick) to spread the load in a rollover. Weld the plates into the base area you measured for the roll bar.

6. Tack the Main Hoop to the Base Plates
Tack the metal securely but don't weld all the way around until everything is in it's right place.

7. Make Supporting Tube Mounting Plates
If a mounting plate must fit around a curve, you can cold-forge it (beat it with a hammer) around an anvil horn of the same size. Or, you can ask the same shop that's bending the tube to bend the plate for you. Either way, you will have to do some hammer-adjusting when you install the plate. You want a nice flush fit to your mounting point so you can securely tack the plate in place, then work it with the hammer to finish the fit before you weld.

8. Re-measure Supporting Braces
Take another measurement on the braces from the main hoop to the mounting plates, and use a protractor or carpenter's angle finder to get the correct angles. Allow a little extra length. The ends of the supporting braces need to fit around the curve of the tubing. Mark the places where the braces match. Cutting and finishing your braces may be the most time-consuming part of the project. But it is critical to a quality result that these pieces fit perfectly with minimal gaps. If you're creating an X-shape in the braces, make one diagonal brace full-length, the make the second bar out of two pieces. Use a piece of the angle iron with a notch cut out of the middle to keep the second bar of your X straight when you tack it in place.

9. Tack Support Braces into Place
You may have to make a few attempts at this before everything lines up just right. Once the supports are all tacked, you can start welding everything into place. If you have welds near the headliner or other interior panels, use an aluminum plate or other non-weldable, non-flammable material to protect the parts you don't want burned.

10. Measure the Door Bar
Plan how to connect the driver-side door bar to the main hoop, and measure the distance from the hoop to the car body. In a unibody car, add a mounting plate of .125-inch mild steel like the plate used for the main hoop and support braces. Cut the plate-mounted end at an angle and fish-mouth the end that attaches to the main hoop. Be sure of your measurements because the bar is required to intersect the main hoop at a minimum distance from the floor. Technical inspectors are very strict, so don't be tempted to move that bar to a more convenient angle.

11. Don't Paint the Cage
"On a race car or stunt car you want to leave the cage unpainted in order to inspect for cracks after a race or wreck," Dennis says. "The exception is Nascar and a few other organizations, but they only run their cars for a few races before they are replaced.

Glossary:

Base Plate: A precisely-ground plate that acts as the foundation of a fixture.

Tacking: Fitting metal parts together loosely to check measurements and allow adjustments before the final weld.

TIG Welding: An arc welding process that uses a nonconsumable tungsten electrode to produce the weld.

MIG Welding: A welding process that uses an aluminum alloy wire as a combined electrode and filler material.

#2 Izzys Cages

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Posted 22 March 2011 - 06:40 AM

Damn. I do it all wrong.

#3 lordmulgath

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Posted 22 March 2011 - 07:06 AM

Damn. I do it all wrong.


I just thought it was a decent guide for newbies. I'm sure you know a lot better. Feel free to change what needs to be changed or add things that you thing should be there.




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