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Re: What is the proper way to weld a roll cage in a car? [Re: migsBIG] #2838613
10/29/20 02:57 AM
10/29/20 02:57 AM
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Medlock51 Offline
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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.

Re: What is the proper way to weld a roll cage in a car? [Re: Medlock51] #2838623
10/29/20 05:12 AM
10/29/20 05:12 AM
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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

Re: What is the proper way to weld a roll cage in a car? [Re: lancer493] #2838650
10/29/20 08:12 AM
10/29/20 08:12 AM
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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

Re: What is the proper way to weld a roll cage in a car? [Re: jwb123] #2838673
10/29/20 09:04 AM
10/29/20 09:04 AM
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Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

Re: What is the proper way to weld a roll cage in a car? [Re: jwb123] #2838679
10/29/20 09:21 AM
10/29/20 09:21 AM
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fredericksburg,va
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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

Last edited by cudaman1969; 10/29/20 09:22 AM.
Re: What is the proper way to weld a roll cage in a car? [Re: cudaman1969] #2838691
10/29/20 10:03 AM
10/29/20 10:03 AM
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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.

Re: What is the proper way to weld a roll cage in a car? [Re: cudaman1969] #2838726
10/29/20 11:09 AM
10/29/20 11:09 AM
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Utah and Alaska
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Originally Posted by cudaman1969
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.

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


1941 Taylorcraft
1968 Charger
1994 Wrangler
1998 Wrangler
2008 Kia Rio
2017 Jetta

I didn't do 4 years and 9 months of Graduate School to be called Mister!
Re: What is the proper way to weld a roll cage in a car? [Re: lancer493] #2838788
10/29/20 12:53 PM
10/29/20 12:53 PM
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Originally Posted by lancer493
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


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.


If the results don't match the theory, change the theory.
Re: What is the proper way to weld a roll cage in a car? [Re: Al_Alguire] #2838794
10/29/20 01:02 PM
10/29/20 01:02 PM
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Originally Posted by Al_Alguire
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.


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.


If the results don't match the theory, change the theory.
Re: What is the proper way to weld a roll cage in a car? [Re: jwb123] #2838806
10/29/20 01:26 PM
10/29/20 01:26 PM
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Originally Posted by jwb123
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


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.


If the results don't match the theory, change the theory.
Re: What is the proper way to weld a roll cage in a car? [Re: jlatessa] #2838830
10/29/20 02:06 PM
10/29/20 02:06 PM
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Originally Posted by jlatessa
Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

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

Re: What is the proper way to weld a roll cage in a car? [Re: cudaman1969] #2838838
10/29/20 02:17 PM
10/29/20 02:17 PM
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jlatessa Offline
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I've done that, I weigh 235 #, but my head only weighed 23.5 #s, and I know I'm smart......

Joe

Re: What is the proper way to weld a roll cage in a car? [Re: jlatessa] #2838960
10/29/20 06:37 PM
10/29/20 06:37 PM
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LOL

Re: What is the proper way to weld a roll cage in a car? [Re: cudaman1969] #2839002
10/29/20 08:03 PM
10/29/20 08:03 PM
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Originally Posted by cudaman1969
Originally Posted by jlatessa
Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

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


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

"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.


Discovering "good trouble" everyday
Re: What is the proper way to weld a roll cage in a car? [Re: cudaman1969] #2839022
10/29/20 08:22 PM
10/29/20 08:22 PM
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Originally Posted by cudaman1969
Originally Posted by jlatessa
Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

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


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

Re: What is the proper way to weld a roll cage in a car? [Re: DrCharles] #2839051
10/29/20 09:32 PM
10/29/20 09:32 PM
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Originally Posted by DrCharles
Originally Posted by cudaman1969
Originally Posted by jlatessa
Wow, a 50 pound head!
Not to be a smart a$$, but you have to have a LOT of Gold fillings. LOL

Joe

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


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


My wife would argue that mine is empty...


'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft.

Re: What is the proper way to weld a roll cage in a car? [Re: GY3] #2839087
10/29/20 10:22 PM
10/29/20 10:22 PM
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Hang on, I’ll go throw one on the scale. Be back in a minute.


"use it 'till it breaks, replace as needed"
Re: What is the proper way to weld a roll cage in a car? [Re: TRENDZ] #2839099
10/29/20 11:02 PM
10/29/20 11:02 PM
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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.

Re: What is the proper way to weld a roll cage in a car? [Re: Medlock51] #2839122
10/30/20 02:32 AM
10/30/20 02:32 AM
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Medlock51 Offline
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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.

Re: What is the proper way to weld a roll cage in a car? [Re: Medlock51] #2839169
10/30/20 07:47 AM
10/30/20 07:47 AM
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It was fun, Cudaman.
Light hearted poking fun, much better than the mean kind you
see occasionally here.

Joe

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