Roll Bar Material

[louisb]

What do you guys think the weight difference would be between a 4 point chromoly roll bar and one made from mild steel? I am trying to decide if it is worth it for a street car. If the weight savings is not significant, I might just order a mild steel kit and weld it up myself.

Thanks,

--louis

[Tony M]

If you dont need chromoly unless your racing - mild steel or dom will work just fine.

[SteveW]

You don't 'need' chromoly either for racing..

There is a noticeable difference in weight between 4130 and mild steel but if your not racing then why worry? The cage we're having built, which is quite substantial, there is a 40lbs difference but there will be alot of tubing..

[louisb]

Well, I plan to take it to the track but it will mostly be a street car. I am thinking one main hoop and two rear struts plus a seat belt cross bar. The weight savings can not be that much for such a small amount of tubing. If I go with mild steel I can just order the kit form Alston Chassisworks for around $200 and MIG weld it. Though honestly the price difference is not that much.

--louis

[SteveW]

That sounds pretty good, I 'think' with chromo you have to tig weld it too so unless you can tig weld you'd need some one to do it.. I think mild steel will be more than suitable for what you need  (I'm no expert though  )

[Bryan67]

Actually, mild steel and chromoly weigh the same. But because chro mo is so much stronger you can use thinner tubing to get the same strength. I have heard from some people that they prefer mild steel as chro mo would tend to break rather than bend and absorb the impact.

[Neil Davies]

You must Tig weld Chro moly because the heat from Mig makes it brittle. My last cage was chro moly but the next one will be mild steel.

[ian c]

You must Tig weld Chro moly because the heat from Mig makes it brittle. My last cage was chro moly but the next one will be mild steel.

hey neil , hey steveW .
how ya doin .

any type of welding will do cro-mo .

type of filler wire , preperation , joint type  , tube size , pre and post heat treating , and WELDER SKILL will determine wether it cracks or not !!!

nhra says tig only , but i think this is a way of "making guaranteed" safety , as it can be done as i said .
but if people do it wrong it can crack ,
and with anyprocess , the more steps there are , the more chance of doing it wrong !!

[Speed-Randy]

id get ahold of danny and ask him

[SteveW]

I'm taking my car to one of the best chassis builders in the UK today, I'll ask him 

[ian c]

mmmm ....

i dont mind you questioning my word . (no big deal , i can verify everything i have said )
but please dont question your expert youre taking it to !!!

imho , nothing worse than one of "them" customers !!

if he says tig only , be happy with that , as its the easiest way to weld a cage into a car ........

no need to question it , hes only building roll cages . he doesnt need to know anymore about it . no matter if hes the "best" cage builder in the WORLD !!! 

[louisb]

I have gone ahead and ordered the Aliston four bar setup in mild steel. It will work for what I want and the price is right. Now I just need to teach myself to weld tubing.  It will be a while before I am ready to install it though. Currently focusing on the chassis.

--louis

[SteveW]

Ian I wasn't meaning it funny it's just I know my chassis builder very well so I can ask him anything! In the end I never did as I forgot, too excited about getting my car to him 

[danny gabbard]

mig welding is very strong when welded correct. But if welded with low heat you don't get the penatration.You have more control when tig welding. most sand cars  are mig welded and a good mig welder, weld looks almost as good as a tig weld. And I've never seen a good mig weld crack.

[ian c]

steve ,
no worries , best you didnt question the guy !!!

its only as complicated as you want to make it / or the design engineers / metalurgists say !!
tig is easy to get right , thats why some sanctioning bodies say tig only on a certed chro-mo cage .....

this material was designed for use on plane frames .....  gas welded


i last worked with it around 1996 , gas welded to lloyds class1 and asme standards .

depending upon application , you have to pre-heat some pipes , post heat others , pretension others ....  lots of different proceedures depending upon welding process and filler wire used .... i suspect the cage that cracked wasnt heat-treated correctly and cracked due to the heat-affected-zone ....  can only be put down to bad engineering/workmanship .

this is one of the queer alloys werre a dissimilar welding filler can get better results depending on what you need ....  stainless wire works pretty damn good

[ian c]

i'm no expertt by the way .
i dont even manually weld anymore
i tack with tig , but a computor does the actual butt for me .

as for touching a grinder
no way !!   i only get dirty in my spare time 

[danny gabbard]

It's alway's better to stress releive by drawing heat down slow. with ox/aceylene torch after welding. They make heat pencils that you can check with,we used about 900 degree marker when we made parts at dan gurneys . Parts that were not getting heat treated. Just practice on scrap tubeing till the welds start looking good. Do you guys have a way to notch the tube when fitting? JD square makes a nice one that holds tube and adjusts angle so you can cut with a hole saw.

[Austin Larsen]

Tig 4130 is the only way to go

[Adele AW]

steve ,
no worries , best you didnt question the guy !!!
 

Dude,

Chris would mind us asking him anything... as he says no such thing as a stupid question! And we are not one of 'them' customers, were friends    

Adele

[ian c]

cool .

didnt mean to suggest anything , its just i think customers asking questions can sometimes appear to be doubting the ways and words of the guy !!

this is wahat i had a vision of , and i didnt want to be part blame to your guy getting annoyed !!

[ian c]

you know like that old man harry enfield carachter ??