Chrome moly vs dom

[4bangerhotrod]

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

[F22 RAPTOR]

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.

Exacta-Mundo! Why?

[dynoman14]

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.

[50j]

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.

[twisterf5]

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.

[merc123]

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.

Drop a 2300# piece of lead from 5 feet onto concrete. Then drop a 5 pound piece of lead from 5 feet and see which ones has more damage on the concrete... I don't think you're using an accurate example. A 5 pound sledge, or a 100 pound sledge, wouldn't be anything comparable to hitting a wall in a race car at 50 MPH no matter how hard you sling it.

[twisterf5]

Drop a 2300# piece of lead from 5 feet onto concrete. Then drop a 5 pound piece of lead from 5 feet and see which ones has more damage on the concrete... I don't think you're using an accurate example. A 5 pound sledge, or a 100 pound sledge, wouldn't be anything comparable to hitting a wall in a race car at 50 MPH no matter how hard you sling it.

ya your right but we did put some pieces in a press a few years back all welded different and this set up is the best we found. i have knocked some clips off in my time but never had a failure like the pic that was posted. that is why i beat a piece to crap yesterday.it was hit well over 100 time and not even a crack. all our molly is out of germany that is what is printed on the pipe that is what our supplier has. maybe our is stronger than us stuff or what ever they are using. all i can say is it take a 10 time the strength to bend it in our bender and i have not broke any yet.

[50j]

It's hard to see in those pictures but from what I can see it looks like it was mig welded and it broke at the joints. It could have been too much heat, wrong wire, big gaps, too thin a tube, who knows. There's nothing that can't be done wrong. I would probably use DOM on something that'll be on a rough track myself but to break on impact like that isn't normal for 4130. If I used 4130 I would tig weld it only so that I could control the heat. No gaps larger than the rod. Tig welding takes time and skill so there will be people that will try to mig it.

[dirty white boy]

ya your right but we did put some pieces in a press a few years back all welded different and this set up is the best we found. i have knocked some clips off in my time but never had a failure like the pic that was posted. that is why i beat a piece to crap yesterday.it was hit well over 100 time and not even a crack. all our molly is out of germany that is what is printed on the pipe that is what our supplier has. maybe our is stronger than us stuff or what ever they are using. all i can say is it take a 10 time the strength to bend it in our bender and i have not broke any yet.

dont let these experts get ya down man,...your chassis seen to take abuse as good or better than the rockets an mastersbuilts you run with,..an hold up just fine!

[twisterf5]

dont let these experts get ya down man,...your chassis seen to take abuse as good or better than the rockets an mastersbuilts you run with,..an hold up just fine!

no man im good been doing this for 30 years now. like any chat site you can't tell if you talkin to a racer or a seat warmer. but with all the talk i just had to try to brake it(think i pulled something trying LOL .this chassis was built with supers in mind but you right there is not a chassis out there that can take what mine can one tried last year and ended up in a scrap heap LOL you just can't fix stupid maybe he learned.

[rayburn62]

There is no way the heat involved in the powder coating process affects the chassis metalurgical structure. The process simply does not get hot enough. More racer science going on there. Proper filler material, shielding gas, heat, fit and technique all play a roll in the welding of moly.

[twisterf5]

There is no way the heat involved in the powder coating process affects the chassis metalurgical structure. The process simply does not get hot enough. More racer science going on there. Proper filler material, shielding gas, heat, fit and technique all play a roll in the welding of moly.

thought that was funny myself

[Matt49]

To anneal 4130 you have to hold it over 1500 degrees. I doubt you'll find many powder coating operations that go over 400.
Just another example of dynoman trying to pretend like he knows something.

[fastford]

i tried to stay out of this but i cant stand it any longer without putting my 2 cents in the mix, ive been welding all my 4130 with mild steel and a mig ever since it was discovered that its blend creates a flexible enough weld to keep from stress cracking for a long time, as for powder coating, i do it because the bond it has is so great that after a crash or long periods of stress it makes it easier to spot cracks, ive saw cracks that was under conventional types of paint, but the paint didnt crack so you would not have known, JMO

[50j]

I have heard that aircraft manufacturers mig weld it too but it isn't done by Boo Boo with his 110 buzz box. Tig welding lets you back the heat off on outside areas and put more to inside joints. You've got a lot more control over it. All pro level 4130 drag cars are tig welded without exception. Whatever works though.