Hey.. i'm planning to make my own roll cage, although i've understood that its best to make it out of 25CrMo4 steel since its stronger so I can build it lighter...

But does anybody know the best way to weld this material ? (GTAW)..

 

tig with er80s-d2..... or thats what i would do.


mike

 

all i know is that with chromoly, it has to be tig welded, where with DOM mild, you can still MIG it if you want...use the same practices as you would with welding up a manifold, but you don't need purge gas

 

And why is that ? heat input can be the same and backing gas (when needed) can also be applied with MIG

 

never knew the exact reason why Chromoly is only Tig'd and never Mig'd, but that is what i have been told by many reputable fabricators, including my next door neighbor who built pro-mod chassis for 20 years

 

It's NHRA rules, mainly.

From what I understand, the rule that chromoly must be TIGed is mainly to keep out shoddy welding work that looks good but has poor penetration. It is much easier to get full penetration with TIG than it is MIG. 7.50 and faster cars must have chromoly cages, not having full penetration on those could be easily catastrophic.

 

^^Yes. And what soviet said also. I don't think you're gonna pass cert with chromoly mig'd.

 

if this is your first cage i would suggest not using chromoly, your wallet will thank you.
good luck

 

thanks for clarifying...find some DOM and get to work i would say, especially for an unexperienced cage builder. besides, when it's all in, and i assume painted??? nobody will know what material you used

 

Mild steel, min wall thickness is .120" for mild steel unless you want your car to get heavy

 

typical use of DOM i see is 1.5" OD with .120" wall

 

Nhra tube dia is 1 5/8" minimum thickness .118" so any straight tube can be made of .120 wall tubing but if there is a bend in the tube you need to use .134 wall tubing. This accounts for the stretching the tube undergoes in the tubing bender.

 

i thought nhra rollcage specs for chromo was 1 5/8" .083" wall?


mike

 

I think 10 points can be 1 5/8" but 8 point and down are 1.75". Wall thickness depends on material, diameter depends on the split when going to 10 point or faster you can use the smaller diameter