Hey guys,

Just a really easy question for you guys.

I'm debating between chromoly and mild D.O.M. tubing for a roll cage. Tubing will be 1.75" x .095 either way. Price around here for mild steel is $5.90 CAD/FOOT, while the chromoly is ~$11.xx ... Cage is being made to FIA specs, but I'm still unclear if mild steel is acceptable as per the guidelines.

Thanks for your time!

 

I don't have a lot of cage experience, but I know mild is fine in SCCA, and I thought it was a better material to use for a road race application.

 

My understanding is that the mild will be heavier, but that's not really a concern for me. Thanks for your input!

 

The weight should be the same but you will normally use thicker mild tubing to make up for its lower strength. So at the end of the day a mild cage should weigh more since you would not just substitute one for the other. Different organizations have different specs for different materials, Mild, Chromoly, aluminum.

 

I prefer DOM mild steel purely because it doesn't crack and break as much as chromoly does on an impact, mild steel has some give to it, and IMO is safer. And the whole point of cages is safety.

 

Do you have any pictures of chromoly cracking? I have seen some pretty bad top fuel and funny car wrecks and none ever had cracks.

 

I don't have any on my computer, but do a quick search on google, it should be easy to find some examples, you'll also find a few sanctioning bodies are looking to ban Chromoly for this same reason.

I'm sure you will also find all sorts of people fighting about pre and post heating chromoly, or none at all, and which is better, always funny.

 

You have to get a rule book for the sactioning body and or class you are running. The rules are usually very specific in what tubing material and size must be used.

 

I'm going by the FIA rulebook. And they recommend 1.75 x .095 seamless, but there is no mention of chromoly. That's why I was wondering.

I've decided to order a batch of the DOM, and will post progess soon.

Thanks for everyone's input!

 

Stick with 1020 DOM. It is a good foundation to build with. Mix .095 and .065 tubing to save weight. Chromoly will weigh the same if it is the same size. It is steel. DOM is inexpensive. Plus you can weld it several different ways. With Chromoly you are limited to gas welding or TIG welding with a post weld heating to keep it from being brittle in the welds.

 

oh jeezus it starts again...

 

Oh cheese!

 

Of course that depends on the rod you are using to weld it. Anyone that says you don't have to reheat a chromoly structure after it has been welded with a 4130 rod, doesn't need to be doing work for anyone. There is a reason airplane chassis are cooked in an oven after they are welded, unless they are gas welded.

For the Average joe a cage whipped up in his front yard with 4130 is no where near as safe as a properly built 1020 mild steel mig welded caged.

 

DOM is fine for FIA

 

Now can you weld the cage in with mig or does it have to be tig?

an how easy it it to build one?

 

Most DOM road race cages are MIG welded.

Cage building is not "easy", but it's not impossible either...just a matter of proper design, materiel, and welds.

 

I tried a few searches on google and was not able to find anything about spliting or cracking with Chromoly. Only thing i could find that was remotely related were cracked welds from poor welding.

 

That's exactly what everyone is referring to- the integrity of the weld, if not done properly.

 

YEah, you have to use mild steel, Chromoly is strong, but mild is better for the potential multiple impacts that will happen in road racing (ie getting hit after you already are wrecked)

 

If you're building the cage to FIA specs make sure you turn to Appendix J: Section 8.3.3 (Material Specifications.) You are not allowed to use 4130. The rules call for "cold drawn seamless unalloyed carbon steel containing a maximum 0.3% of carbon." Their definition for an unalloyed steel is one that contains a maximum 1.7% magnesium and 0.6% for other elements. While 4130 falls into the realm of containing less then 0.3% carbon it is still an alloy steel. Any mild steel; 1018, 1019, 1020, 1021, 1022, 1023, 1025, 1026, 1030 are all acceptable per the rule book with 1022, 1026 and 1030 having the highest tensile strength. The most important thing past this is the welding. If the welding cant hold up; either will the cage.

oh, 4130 and MS weigh in the same @ 1.679 lbs/ft. The differance in weight between a moly cage and a DOM cage is the tubing thickness.

 

Thanks for the info guys! I ordered 1030 MS. It's actually a lot lighter than I expected!

Here are some tests I did today :

 

Nice! now you gotta do it upside down with the pedal inbetween your thighs lol. Can't wait to see it done

 

Don't forget to grind the thin edges of the coped tubing back to full thickness before you weld it. A lot of people forget this step. Looks good though!

 

Not entirely necessary with TIG, since you are going to burn away that razor edge anyways. MIG welding, for sure!

 

well in the near future if your not sure which material to get just ask the Jeep guys on there forum they would deff know.