welding a roll cage

[Fheckro]

Is MIG ok for a roll cage?

I on the verg !

[jimmy six]

If it wasn't a lot of cars would not pass tech...................

[Peter Jack]

Just be sure it's not a 120V mig and the operator is fully experienced. A roll cage isn't the place to learn mig welding as a mig weld can look good and not have proper penetration. If your welder is at least a 220V and you have enough experience to know that your welds are sound have at it. For many the building process is the best part.

Pete

[Gwillard]

It depends mostly on material. Most NASCAR roll cages are made of 1020 and 1026 mild steel and are mig welded. For Cr-Mo 4103 roll cages mig is not the prefered way. Tig is much better suited for 4130.

[bearingburner]

Take a couple of scrap pieces weld them together and cut the weld apart and check penetration.

[Fheckro]

Thanks. I have been welding for a long time,  just never a roll cage that will be subject to tech inspection. I figured it's better to ask up front.
I do enjoy "the build" almost as much as the speed and want to do the best job I can. I will not compromise my safety

Fred

Also...The car is a unibody design (Chevy Monza), In the SCTA rules it states that for unitized construction the support bars shall have a 1/4in thick support pad on top and bottom of the floor ( in a sandwich construction). That is all good but I also have frame connectors that are 2in square 3/16 wall tube and are right up against the floor. I would like to work them into the equation. Any suggestions?

[Gwillard]

Take a couple of scrap pieces weld them together and cut the weld apart and check penetration.

That will show whether or not the weld is getting sufficient fusion but unless it is polished, etched, and inspected under a microscope it tells nothing of the microstructure that determines how tough or brittle the weld is.

[Peter Jack]

Fred, probably the best approach is to talk to the appropriate tech people in the organization with which you plan to run. An e-mail or a phone call to those people is probably a lot more valuable than the speculation you will get from here, although the speculation is probably a lot more entertaining.

Pete

[saltfever]

. . .  In the SCTA rules it states that for unitized construction the support bars shall have a 1/4in thick support pad on top and bottom of the floor (in a sandwich construction).

There is some confusion in the rule book about this. I think they are referring to bolted-in base plates and not welded base plates. The pictures show two cages that passed inspection at Speed Week. They had no additional plates welded-in under the floor. I know, because I looked for them. Contact "Kiwi" Steve Davies, chief car inspector. But wait till he has had time to decompress after Bonneville.  Let us know what you find out.

[interested bystander]

Lotta good advice here.

If your Mig or Tig welds look like pieces of DOO DOO a couple things might be wrong.

I.E., wrong setting on machine, bottle, etc. , ignorance,  old wire in case of MIG, particularly, wrong tungsten, wire and so forth. Most everybody knows a weldor with a good reputation nearby and some (hmm, maybe me, even) will weld for a bit of their favorite beverage . Seek them out. It's your a##, drivers!

Have on occasion done drag race tech and Bird-poo welds are cause for DQ in my eyes, even though the tubes are all dead plumb and perfectly fit. (Although sloppy fabrication usually goes with those kinda welds).

[tedgram]

. . .  In the SCTA rules it states that for unitized construction the support bars shall have a 1/4in thick support pad on top and bottom of the floor (in a sandwich construction).

There is some confusion in the rule book about this. I think they are referring to bolted-in base plates and not welded base plates. The pictures show two cages that passed inspection at Speed Week. They had no additional plates welded-in under the floor. I know, because I looked for them. Contact "Kiwi" Steve Davies, chief car inspector. But wait till he has had time to decompress after Bonneville.  Let us know what you find out.

Correct, you only need bottom plates if bolted not if welded.

[Rex Schimmer]

I think that from a safety stand point welding 1/4 plate to .035 or .025 sheet metal is asking for problems. Look at the picture that Saltfever posted with the 1/4 plate welded in the middle of a big panel, to me this is very bad design. Any large loads that are subjected to this plate through the connected roll bar  will simple rip it off of the floor, tearing a nice 4x6 hole in the floor. My preference is to always make this type of connection at some place on the car which has an angle or some sort of shape that provides some structural strength to the car its self and if you can't find something then weld in a tube that does connect to some strong part of the car and connect to that. The connection in this picture does meet the letter of the rule, but it is still a poor (and dangerous) design. Also note the weld itself, the bead is approx 1/2 to 3/4 of the thickness of the 1/4 plate, this means that the welder held the heat against the 1/4 plate and allowed the puddle to touch the floor panel just enough to adhere to the floor and not burn a hole in it, probably not a good weld. Large and inconsistent weld beads only help to start the plate tearing from the floor.

Rex

[Milwaukee Midget]

I won't name names, and my car hasn't passed tech yet, but I was told by an SCTA authority that "you want your body attached to the cage, not your cage attached to the body".

This was the solution we came up with.



Even in a convertable with the top removed, constructing a safe cage is tough.  I think Rex is spot on when he says that welding plate to sheet metal is problematic, and I was grateful for the SCTA official who pointed me in this direction.

An eight second cage in a fifteen second car.  

Contact them.

[Peter Jack]

The tool behind the cage is essential, especially with anything British!!!

Pete

[Dr Goggles]

An eight second cage in a fifteen second car.  

That's a good looking cage.

I'm not an engineer, and have a low level welding ticket.....so I haven't leapt in when people are discussing cages. But, I'll say now that some of the cages I have seen pictures of here are what I would describe as barely enough or proof that the builder or designer hadn't put a lot of thought into it.

Long unsupported sections, a lack of triangulation....and then as stated above anchor points on unbraced areas of the floor

As i said I'm not an engineer, but when weight isn't a huge penalty and most people have spent a lot on a motor what kind of dill skimps on some tube??

Building a cage is a chance to brace the car, and save your own life....... it's not playground equipment.