What is the proper way to weld a roll cage in a car?

So I'm looking to eventually get a cage in a future track car build and a 'extreme street' build when my two projects are done and though I might try my hand at welding it myself. I have a friend that can teach me the basics of welding cages, but would like some info on some issues. I have a friend with a homemade roll cage in a Superbird and it had badly aligned doors that would not shut properly. He decided to that the cage was a pain due to the way the previous owner put it in, decided to cut it out. After removing the cage, the door alignment issue they had went away and now shuts properly. I want to avoid some of these problems and looking for some advice.

Should cages be welded with drivetrains in them?
Does the car need to be planted on all four corners or supported on jacks/lift?
Will having all the suspension done first affect the geometry or not an issue?
Steel vs chromoly?

Thanks for any info you have.

After seeing my friend wreck at 135mph and the cage welds holding I only could suggest having a professional chassis shop put in a cage.

Reread your post how the amateur put in a cage and there were issues. But those who are chassis builders here please answer his questions for the better of the forum. Also the link below is one of the best chassis builders and has some good information.

https://www.youtube.com/watch?v=SQw9DFo8R5A

A unibody car needs to be properly supported. How that's done depends on if it's a running car on it's wheels, a bare shell or somewhere in between.

Suspension done? Stock, struts & 4 link or somewhere in between? A chassis car is built to the suspension locations. A stock suspension, full body car is built to support the original locations.

Chrome-Moly, but that requires TIG welding and proper fitting.

You can learn the basics sitting at a table with a MIG running beads. But when you get inside of a car, in all kinds of positions, on a round piece of tube, it's not the same. Learning how to fit, plan, make it symmetrical, fit tight to the body, weld places you can't get to, make it look right, use a tape, plumb line, angle finder and a level is 80% of it.

Have you fabricated anything out of steel before? A race car is not a good beginner project.

Make sure the car you are starting with is straight and not a parallelogram to start with, especially if its unibody and you're tying into the shock towers, even if it hasn't been in an accident. Its pretty hard to pull it back into spec once its caged, and the wheel alignment isn't working out. My friends frame Jig is made out of I-beam with that is at least 10" on the web.

Have a pro do it. If you want to learn, watch the pro.

Some things in race cars are not worth risking your life over, especially race and safety equipment
I know of a good young roundy round racer that was killed in his car at the old Riverside raceway in Riversdide ,CA back in the mid 1970 when one of the bars broke loose in a wreck and pierce his body above the left kidney
Be safe, don't die young over bad decisions

Build it yourself but be sure to wear a mask, don’t want to die from Covid.

I'll chime in here. We have an endurance racing car. One of our team members is a great welder and did his own circle track car... however he didn't want to do the cage in the endo car, said at our speeds he didn't want to be responsible. Plus we wanted to make 100% sure we'd pass tech. Suck to get the car all set up and fail tech. If you are racing this car and it needs to pass tech and you have never done this before, take it to a shop. Our cage cost about $3500

this is why... this is our car after going from 3rd to 2nd by mistake...this is only at maybe 89mph. The cage held up great and is being used in the new car.

Think of this, NASCAR requires mild steel for a cage, 4000 pound cars going 200 mph that wreck a lot. Ask yourself why?

There are also rules on where the loop behind your head goes and it's relationship to where the driver's seat is at etc. A chassis guy will know all the fitment rules and get it right the first time.

Self-taught types just starting out can make a weld that looks ok with a little practice, but do they really know if the weld is strong enough? Look at the guys who narrow their own rear ends at home for the first time and the spring perches break loose on the starting line.

I will add, your helmet cannot be w/in 2 inches of any bar. Before you or anybody welds a cage in, get in the car with your helmet on and see where your head is. It would suck to get it all welded up and your head be too close to the bars...

I built almost everything on my car. The one thing I farmed out to a professional? The 6 point roll bar!

I paid a local race car shop to do it and they thought of things I didn't because it is something they do every day.

Amazing looking welds and peace of mind for me.

Yeah, and anything quicker than 7.50s is required to be 4130. Why?

I don't want to dissuade anyone from building their own car, engine, trans, rear or whatever. But you have to be realistic about your skills and abilities. No one is born being Jerry Bickel or Don Ness. They have to learn and build on their skills to where they can do what they do. Some people become good accountants or lawyers so they can pay people to build them cars.

You have to work with someone to learn fabrication skills and things specific to doing race car work. Talk to people who have done it and have them show you around a car. A mentor or an advisor who isn't an idiot is almost a necessity for those just starting out. You have to learn how to make stuff out of metal. It's all just metal.

You should know your own abilities and mechanical aptitude. You should be very familiar with the roll bar/cage section of the rulebook. If you are able to do it, then do it. It's rewarding to do a project like that, learn how to do it and build on your skills.

Read the rule book. Look at lots of other cars. Use the right material. Make sure the joints fit very tight. Add extra bars , gussets. Tie the cage to the body at the A pillars, B pillars, cowl, any where you can. Tack everything before any final welding. If you have any question on welding, have someone that you have seen their work do the final welding. Designing to drop tha tacked cage thru the floor to gain access to all upper welds is a good idea. Take your time, no hurry. I built and designed my cage myself. It got good comments from the Division 3 tech director who certed it and a few well known chassis guys to boot. I am not a tig welder. I bent most of the tubes, fitted them all and tacked it. Had a professional weld it all up.
Doug

Perfect example there, cross bar has to be welded first, then the brace diagonal welded in next. It goes together in steps, something a person with experience will know. PPPPP, proper planning prevents poor performance.

if I understand you correctly, I thought a few years back, the above was changed, in that they now wanted the diagonal bar one piece, and the cross bar two pieces?

And the the reply earlier about needing two inches of clearance between any bar and the helmet, is that a written rule or common sense, although the 2" is somewhat arbitrary?

On the MS vs CM for Nascar, I thought there were three main reasons, cost, weight savings is not overly important, and the fact the stock cars get banged up over the course of a season and put back on the track, and MS can handle that, and welded CM, although a stronger material, doesn't like repeated abuse, and hard to tell when its near its useful end.

Mild steel will give and bend (absorb) when hit. CM will crack over time, the reason for the X-ray requirements. My first car was MS but was hard to sell, the two I have now are CM because that’s what the racers want. Remember the number one rule, triangulation. Your 50 pound head in a 5 pound helmet flopping around to close to a bar in a wreck is not good. I don’t think 2” is far enough away, remember Dale Earnhardt. these are just my opinions.

My thoughts, and experience for what it is. Mig Welding on a table with nothing in the way, and using clean new metal, is a skill that does not take too much time to master. Welding a cage in a car upside down, getting sparks down your neck, and trying to get the undercoat and paint off well enough for a good weld is a lot bigger challenge. First is look at the cage two ways, making the car safe, NHRA rules lay that out, second, making the chassis stronger and stiffer without adding too much weight is the next challenge. I always weld on jack stands, car leveled, and make sure the doors still work and gaps fit well during the process. For most cars and home building mild steel is the way I would go. Moly is lighter and stronger, but also more brittle, and higher level welding skill is required. I have built several cages over the years, I remember one that when welding in the frame connectors, I got a spark down my shirt, and in pushing the creeper to try and get away from it, I hit one of the jack stands, and to my surprise, it simply slid out form under the car, and the car just sat there on three jackstands. I took that to be a test that the car was square and stiff as it needed to be.

I have a 64 dodge NSS car that we built at the tech school where I retired from as a teacher. The last project the students helped me with on the car was a moly cage. The welding instructor who was helping made the students fit the joints so a .010 feeler gauge would not fit in the joints before he would let them be welded. The welding instructor did most of the upside down, curled into a ball welding. My issues is as a 64 years old, I can not see well enough to weld in those positions anymore. Moly cage saved 100lbs, and made the car a lot more consistent, in 60 foot times. Since moly is so much lighter I added a little tubing here and there to make it stiff. The other issue was the original cage was built as a leaf spring car and over the years had been changed to a 4 link. The cage had bars were they were not needed, and needed bars in other places. The redo, fixed all those issues. And I was proud that the NHRA tech inspector who certified the new cage commented on the good quality of the job.

The other issue is resale value, if it is a good job, a moly cage car will always bring better money on resale.

I dont know what NHRA requirements are but our dirt cars are constructed of DOM, chrome moly or Docol tubing. Dont rely on an EWT tubing cage.

DOM is fine for most applications. Chrome moly can be welded with MIG welding just fine...no TIG required. DOCOL is the latest/ greatest tubing but has some drawbacks, too.

There seems to be two different opinions in this post on welding CM tubing. One implies it must be Tig welded, the other implies it can be Mig welded. Never tried Mig welding CM but was wondering if it was acceptable in the welding of smaller, lighter duty brackets. Not trying to hi-jack this thread, but hope someone might clear this up. Seems like an important issue here. Bill

Mig welding chrome moly makes it brittle, too much heat. Lot of the older guys that build airplanes welded chrome moly with an acetylene torch, makes welds like a tig if you know how to do it. But they had to heat the joints to keep them from cracking. I acetylene gas weld headers when I build them, had an old air craft mechanic watch me one time and he asked if I used to build airplanes.

MIG Welding 4130 Chrome-Moly
By Galen White, welding engineer, Miller Electric Mfg. Co.

Grade 4130 steel, while containing both chromium and molybdenum as strengthening agents, is considered a heat treatable low alloy (HTLA). Generally referred to as chrome-moly, this HTLA is used largely for aviation, racing and welded tube structure applications.

When welding 4130, preheating to 300°F is strongly recommended by the American Welding Society (AWS) to relieve stresses in the metal. When choosing a wire, most people opt for ER80S-D2 or ER70S-2. ER80S-D2 will provide the most weld strength. The ER70S-2 is easier to find and provides a strong weld, but you’ll be sacrificing some strength by choosing this filler metal over ER80S-D2. When it comes to shielding gas, 75/25 (Ar/CO2) is recommended for most applications and 98/2 (Ar/CO2) for anything over 3/16 in.

Wire Size-Amperage Range- WFS Range Relationships for Short Circuit Transfer on Steel
Wire Size Amperage
Range Wire Feed Speed
Range
.023" 30-90 100-400
.030" 40-145 90-340
.035" 50-180 80-380
.045" 75-250 70-270

Cleanliness is critical when welding 4130. Make sure that all mill scale and oils are removed using mild abrasives and/or acetone. When you strike an arc, keep your heat input low to reduce stresses in the metal.

Post-weld heat treatment of 4130 varies from one application to another. If ductility and toughness are your goal, post-weld heat treatment is recommended up to 1,200°F. If the material you are welding is thinner than .120 in., stress relief through heat treatment is not as critical.

WFS Rule of Thumb:
1 ampere for every .001 thickness
1/8" material=.125=125 Amperes
Wire Burn Off:
.023-3.5" wire/amp - 125 amps=437 IPM
.030 - 2" wire/amp - 125 amps=250 IPM
.035 - 1.6" wire/amp - 125 amps=200 IPM
.045 - 1" wire/amp - 125 amps=125 IPM

Welding 4130 is a lot like welding mild steel and is easy if you know how. These are just some of the reasons 4130 is considered so flexible and is used on everything from airplane engine mounts to bicycle frames

Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

I might add, when welding MS, unlike CM, leave a 1/16 gap between the pieces. The wire will penetrate and not ‘bubble gum’ up on the joint. Next time you’re at the races look at each cars ‘welds’ then ask yourself would you feel safe in there?
I would only use .125 DOM tube also, doesn’t have to be .134 because it’s uniform. Just a hoop 1.3/4, cage can be 1.625

Per NHRA rules moly MUST be tig welded so it does not really matter IF it can be welded with a mig welder for the purposes of this discussion. As for attachment of bars in a unibody car it is acceptable by rule to weld the bars to 6"x6" plates to the floor.

That is almost true, aircraft of yesteryear were mostly chromoloy and were welded with a torch, the heat affected zone was a lot larger back then and a 3/4" .049 wall tube in a cluster weld could survive an impact at 100 mph plus. Modern welding uses TIG and the HAZ is a lot smaller, if you pre and post heat and not contaminate the weld with the tungsten, it will last just as long as mild steel and look as beautiful as a modern weld. Tim

Not sure whose information you are seeing, but as far as NHRA and SFI are concerned - ANY weld on CM to CM joints or that affect a CM chassis structure part, i.e. welding a mild steel tube, tab, etc onto a CM tube, must be done with the TIG process. Period.

There may be other places, or industries where MIG on 4130 is acceptable. Pipelines, etc., with a person trained and skilled doing it. But NOT on a piece of .083 tubing where heat needs to be tightly controlled.

Mild steel is not all the same. DOM, ERW, 1010, 1020, etc.

DOM - Drawn Over Mandrel is much more accurate thickness wise than ERW - electric welded seam. This is why kits and tubing made from ERW need to be .134" wall to ensure it passes a .118" sonic check for cert. This obviously adds 10% to the weight of it. DOM will pass and is typically within .0005". I've seen .120 ERW as thin as .113-.114. Years ago, when chassis certs became a thing, a lot of cars that guys had been racing for years and built from kits using .120 welded seam material, became junk. Cut it off at the frame rails and start over.

DOM is typically 1020 where ERW is usually 1010. This indicates the amount of carbon in the alloy which affects the hardness among other things. The difference is easily seen by running an 1/8" drill through pieces of 1010 and 1020 material of similar thickness. CM is 4130. The last 2 digits indicate the percentage of carbon. The price difference between DOM and 4130 is minimal. ERW is cheap s***. It may be okay for a cheap 8 point in an 11 - high 10 second car. I won't use it.

Both true. Specs and construction techniques in the rule book are understood to be minimum acceptable. Fabing a frame structure in the floor, and building the cage on that rather than the thin sheet metal, will greatly add to the strength of the car. Safer, more consistent and responsive to chassis tuning.

Good information. The old guys running a welding class I attended many years ago made you learn to gas weld before touching a TIG torch. A very good idea even today. Learn how to work your hands before adding the foot (or thumb) control. Plus they had a tight budget and didn't want all the class time used up ruining and grinding tungsten.

I like to use a propane torch to warm a joint before welding but mostly to burn off any contaminates or moisture. You can see the crap come out of it. Preheat on 083 or 058 is debatable. Another technique I've seen recommended is starting a weld at the thin part of an intersecting tube on a notched joint. This is where the minimum heat is needed and working the weld to the corner or the thickest point of the joint serves to preheat that area.

I like ER-70 over 80. Either wire will mix with the base and the resulting weld will a higher strength (tensile) than the wire by itself. 80 will be stronger and harder. I think 70 provides a bit more ductile weld with some give that can help with not cracking the tube in the HAZ over time. The expected use and lifespan of the chassis will effect this decision.

20% of your body weight last heard, take yours off put it on the scale to see what it weighs

I've done that, I weigh 235 #, but my head only weighed 23.5 #s, and I know I'm smart......

Joe

LOL

That "20%" sounds more like the energy consumed, rather than weight, but I am sure some do use more or less then others.

"Despite this, even at rest, the brain consumes 20% of the body's energy. The brain consumes energy at 10 times the rate of the rest of the body per gram of tissue. The average power consumption of a typical adult is 100 Watts and the brain consumes 20% of this making the power of the brain 20 W"

https://hypertextbook.com/facts/2001/JacquelineLing.shtml#:~:text=Despite%20this%2C%20even%20at%20rest,of%20the%20brain%2020%20W.

A human head weighs about 12-15 lbs. Unless the brain is made of iron. Or lead.

My wife would argue that mine is empty...

Hang on, I’ll go throw one on the scale. Be back in a minute.

Woo we I made a dull post funny. I got a friend who’s called fat head wears an 8-1/4 hat and has no neck, head tapers out to shoulders. I have to force myself to not stare.

I can tell you that there are thousands of oval track cars that are built using CM and were MIG welded. While we don't generally run much over 125 mph or so (except on a mile track where straightaway speeds can reach 175 mph or higher...and big miles are few) most racing sanctions require a .063 minimum wall thickness on the main cage and supports. The main frame rails on my older chassis are .049 and my newer car are .083.

Kinda funny that the lower class cars generally must run .083/.095 tubing for their cages.

Not trying to argue with anyone just sharing my experience.

It was fun, Cudaman.
Light hearted poking fun, much better than the mean kind you
see occasionally here.

Joe

We have to run 1.75 DOM in our car.

Don't worry, we are all adults here on this forum.

That said, I am not a big believer in speed as a useful indicator of what are the best materials or design.

In that all concrete is fairly consistently hard, and #3 Dale died hitting concrete at an effective closing speed of approx 43mph.

I saw a race where from an on track cameras showed Richard Petty’s car just barely touching a wall. Nothing much, but the in car camera show him almost come out of the seat, arms and head viscously moving in the direction of impact like a crash test dummy.

I built 2 dom steel cages 15 years ago for a guy, welding method wasn't specified in their rule book, the only method I knew back then, was Stick welding with root and cap, the mig I had back then wasn't beefy enough.. I did a gapped fit up with a 6010 root, and then a 7018 cover pass.
The guy ended up hitting a large tree with one of the cars at high speed in passenger side frontal impact. None of the welds gave, the tubing bent and the frame rail sections ripped out of the unibody in places. The driver and navigator walked away from the crash. Weld porosity is a big problem
with stick welding, done wrong, its weak, done right, really strong. We use it a lot in plant construction, but we also have to do 10% xray on joints.
Porosity is pretty much non existent with tig, but can have shallow penetration and be a very pretty, but weak weld. Easy to undercut the joint with too.
When I do my cage for my next track car, I'm probably going to do a tig root and Mig cover pass. I don't build cages for people anymore with all the liability stuff...

I'd never even think of welding a roll cage. I do a lot of bench welding and I can make a nice bead when I have my arms in the right position but there is zero chance I could get nice welds when I'm laying on back reaching around a corner or something like that. The chassis guy that did my cage really had to work to get to a few of the welds. They tig welded the cage and on some welds he had a helper run the foot pedal while he handled the torch and rod. Those guys work as a team and do that type of welding all the time. I never do that type of welding and I'm not going to start on something like a roll cage.

You have to plan the job and how it's going to be put together. Some of it may be partially welded and pulled out of the car to finish. And/or it may be dropped through the floor. Or, like a lot of cars with funny car cages, etc., cut the roof off.

The chassis serves two purposes. Protect the driver and be the main structure of the car supporting the suspension with the desired rigidity.

The rulebook spells out minimum requirements. They are seldom sufficient to do both jobs well without adding to it and improving on it.

Thank you everyone! The information I received here was incredible. I never would have though up all this stuff. Even though one car would be more of a 'cosmetic' thing, I am going to completely rethink what I really need in a cage and see what fits my needs. I am starting out with the worst possible car bodies with this build (burned b-bodies) but enjoy the challenge of something different. I'll see about checking out pre-bent cages, a professional fabricator that could adjust/modify the cage to accommodate my needs. I'm thinking of going to Chris Alston's Chassisworks and see what I could use for each car (they are a short drive for me). Skimping on safety was not my intention. Finding a way to come up with the extra cash is far more easier than the added materials/work required for the job. Thank you for your info everybody, I feel this has enlightened me to a better understanding to my needs for this build.

I used Art Morrison for my 10 point kit in my Dart.
I used a Competition Engineering kit for the 6 point I had in our last car.
And if I do another , I will have learned enough to do it better than the last one.
Hindsight tells me I should have gone through the dash and created much more room to get in and out of the car.
But if I did go that way , I would seriously consider an experienced fabricator to do the job for me.
My welds are Dog's Butt ugly , but I trust them.
I use mild steel so I can MIG it , but the tight quarters and awkward positions required were much less of a problem , even in my 40's.
That was twenty years ago.
It's not the place to learn to weld , that is for sure.
And you can save a lot of money by mocking it up and doing the fitting your self if you are going to have it welded by a pro.
The guys I use for stuff I can't do are around 100.00 an hour and well worth it.
And the fitting is the time consuming part of the project.

Burned? As in on fire? Bad? Not a good choice for so many reasons.

A professional is not going to use a kit. Most won't anyways. They prefer to do it their way. Kits are for guys who have some fabrication skills but no bending equipment.

Well, it will be lighter. Like I said, these will not be typical cars. One for track use, one for street strip. If worse case happens, I can always just move onto another shell.