If no, then don't touch it, improperly welded chromoly can fail easily and injur or kill. Personally I would only TIG chromoly, which many don't but that is the safer way to do it.
Also if your not using the strength of chromoly to go lighter then your only saving wallet weight.
If you can properly weld chrome moly, use if for the driver protection areas and DOM for the rest of the car. The stiffness of the two materials is the same. The yield point is what is different.
I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO
Last edited by F22 RAPTOR; 01-01-2013 at 12:51 PM.
Reason: Clarity
I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO
Straight out of the GRT book:
"4130 material needs to be heat treated after welding....the weak point will be the area right where the heat concentration stopped while welding..."
This explains why it broke where it did. According to the book GRT builds 95% of their cars out of DOM and it is more forgiving in crash situations than chromemoly.
Also, my opinion, if you are asking what type of tubing to use maybe building a chassis isn't the thing you need to start with.
"4130 material needs to be heat treated after welding....the weak point will be the area right where the heat concentration stopped while welding..."
This explains why it broke where it did. According to the book GRT builds 95% of their cars out of DOM and it is more forgiving in crash situations than chromemoly.
Also, my opinion, if you are asking what type of tubing to use maybe building a chassis isn't the thing you need to start with.
Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.
Great pictures of failures. A lot of learning can be done from them, thank you for posting.
No problemo. I keep them just for that reason, to learn. I actually got them off Facebook, but nobody was even talking about the failure, just Ooo-ing and Ahh-ing the wrecked car... Go figure.
All sprint cars and midgets are built out of moly, they don't break like that.... I have been in the fab business for almost 20 years and thats just a case of annealing the material. If it's welded right it won't break like that. It will bend to a point and break though. DOM is the way to go though IMO.
chrome moly tube been used for years in NHRA an IHRA but there needed strengths are different than what strengths dirt racing needs,...think somebody needs to do some crash study analissies on dirt chassis like NASCAR an NHRA an such do....for safety sake...
I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO
you asked to see pics of our new chassis. could not get them to load yesterday but you can go on my FB page they are there ( richard clew )
our new car is 100% moly as has been our owm cars in the past our last owm was 4 years old when it started cracking so we got rid of it. most people weld it wrong and think they can use the same wire they use on mild steel. we use a special moly wire that you do not have to heat bars before welding.it is around 15 dollars a pound /instead of the 3 bucks the other wire cost there was no expense spared on this chassis could of built 3 chassis for what this one cost.well we will see in march how it works out.
chrome moly tube been used for years in NHRA an IHRA but there needed strengths are different than what strengths dirt racing needs,...think somebody needs to do some crash study analissies on dirt chassis like NASCAR an NHRA an such do....for safety sake...
think that would cost to much/ i have welded several bars together with different wire and then put them i a press until they broke. that is as best as i can do with our budget LOL but feel 100% we will be OK with this chassis.
think that would cost to much/ i have welded several bars together with different wire and then put them i a press until they broke. that is as best as i can do with our budget LOL but feel 100% we will be OK with this chassis.
seen the pics on FB,..its a nice chassis,..very professional looking!
Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.
Maybe so, probably because that's what everyone wants now.
Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.
It fails next to the weld because of the martensite that forms when the area cools from a molten metal to room temperature too quickly. The only way to avoid this process would be to heat in an oven and cool it slowly.
No matter what rod you use, this process still happens. It just may not be as big of a problem when an experienced welder uses a time-tested technique.
As I have said on here many times, why? Moly is NOT lighter. It is NOT stiffer. Only the yield and ultimate strengths are higher. (about a factor of 2). If your chassis has members that see stresses near the yield of mild steel, you need to go back to the drawing board.
Last edited by MasterSbilt_Racer; 01-06-2013 at 09:05 AM.
they make machines that stress relieve the welds which will keep it from breaking next to the heat line on the weld. but im sure none of your average shops have this equipment
It fails next to the weld because of the martensite that forms when the area cools from a molten metal to room temperature too quickly. The only way to avoid this process would be to heat in an oven and cool it slowly.
No matter what rod you use, this process still happens. It just may not be as big of a problem when an experienced welder uses a time-tested technique.
As I have said on here many times, why? Moly is NOT lighter. It is NOT stiffer. Only the yield and ultimate strengths are higher. (about a factor of 2). If your chassis has members that see stresses near the yield of mild steel, you need to go back to the drawing board.
The main reason people think Cro-mo is lighter is because it is usually available in lighter gauges than steel tubing. You don't have to have annealing equipment in your shop you just take it down to the heat treater just like you would the powder coater.
Annealing a chassis consists of heating it up and then cooling it in a controlled environment. All it is , is a high tech metal relaxation technique. You have to do it every 2 years in NHRA Professional classses. Most racers sell them as multiple annealling will embrittle the frame. That is why some of the older ProCars crack and break and hurt people.
I know a couple guys won't powder a car just for that reason.
I personally use ERW thin wall stuff for bumpers and body supports so it provides a crush or crumple zone to absorb some of the G's of a wreck. I like .095 DOM in the drivers compartment as well as steel sheet in the floor and around the driver as I have seen drive shafts and flywheels cut folks hands and arms off. You have to add lead anyway so may as well keep driverman safe.
The further away from the cG of the car the bigger the pendulum effect so then you can make fuel cell cage outer from lighter 1" material, I have even used aluminum. With a carbon fiber bladder, Ti-Sheet cover and alum you can save almost 40# over standard config. on a Pave car. I will be building the same stuff for my dirt car as I feel the fuel cell area is very neglected by most racers and I have seen numerous fuel cell punctures and thank God they never caught fire til the driver got out.
If you have any friends in the computer modeling business have them run your chassis design thru plastic deformation program. You will find that triangulation in chassis segments is a bigger influence on strength than the materials you use ( within reason that is ). I designed my chassis in 2-3ft sections and analyzed each one by itself and then as a whole and I was able to eliminate 20% of tubing used in a pavement car while increasing chassis rigidity over 200%. You should also consider using gussets at most of your load carrying joints. You will increase chassis rigidity greatly and only add about 20# of material.
I would also talk to someone with some chassis building experience to get you some help in wire and gas selection for the tubing you select. It is also a critical part of our chassis that is way overlooked by most everybody doing it in their back yard shop. Wire and gas are critical to heat and penetration as well as weld purity.
The main reason people think Cro-mo is lighter is because it is usually available in lighter gauges than steel tubing. You don't have to have annealing equipment in your shop you just take it down to the heat treater just like you would the powder coater.
Annealing a chassis consists of heating it up and then cooling it in a controlled environment. All it is , is a high tech metal relaxation technique. You have to do it every 2 years in NHRA Professional classses. Most racers sell them as multiple annealling will embrittle the frame. That is why some of the older ProCars crack and break and hurt people.
I know a couple guys won't powder a car just for that reason.
I personally use ERW thin wall stuff for bumpers and body supports so it provides a crush or crumple zone to absorb some of the G's of a wreck. I like .095 DOM in the drivers compartment as well as steel sheet in the floor and around the driver as I have seen drive shafts and flywheels cut folks hands and arms off. You have to add lead anyway so may as well keep driverman safe.
The further away from the cG of the car the bigger the pendulum effect so then you can make fuel cell cage outer from lighter 1" material, I have even used aluminum. With a carbon fiber bladder, Ti-Sheet cover and alum you can save almost 40# over standard config. on a Pave car. I will be building the same stuff for my dirt car as I feel the fuel cell area is very neglected by most racers and I have seen numerous fuel cell punctures and thank God they never caught fire til the driver got out.
If you have any friends in the computer modeling business have them run your chassis design thru plastic deformation program. You will find that triangulation in chassis segments is a bigger influence on strength than the materials you use ( within reason that is ). I designed my chassis in 2-3ft sections and analyzed each one by itself and then as a whole and I was able to eliminate 20% of tubing used in a pavement car while increasing chassis rigidity over 200%. You should also consider using gussets at most of your load carrying joints. You will increase chassis rigidity greatly and only add about 20# of material.
I would also talk to someone with some chassis building experience to get you some help in wire and gas selection for the tubing you select. It is also a critical part of our chassis that is way overlooked by most everybody doing it in their back yard shop. Wire and gas are critical to heat and penetration as well as weld purity.
Argon and 70-s2 rod or in some cases 80-s2. Where does one find this every 2 year heat treat rule for the "ProCars".? Here's a hint, the Pro Stocks and Pro Modifieds are 25.1E. 4130 is used because the required wall thickness is less than mild steel so it's a lighter chassis. Going back over welds or welding with too much heat will make it brittle and it'll break by the weld. Too hard a rod will crack at the weld. Drag race chassis are welded with the right heat and allowed to cool at room temperature. Tig welded.
just for the he-- of it i took a piece of 083 1-3/4 and a piece of 065 1-1/2 and welded them this morning. let it air cool for 20 minutes then put them in the vice and beat them to death with a 5 pound sludge hammer bent the end of the pipe flat wore my self out trying to brake it. not a chance no cracks / nothing. so i guess i will stay with my way of welding moral of my story is don't go cheap on the wire and the gas.
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Chrome moly vs dom
Senior Member
Chromoly, just say "NO".
Originally Posted by F22 RAPTOR
Exacta-Mundo! Why?
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