chromoly tubing for cage ?

[RickM415]

hello,where can i get some chromoly tubing in northen california and what size
i am wondering if its 1 5/8 .83 or .120

i want to build a 10 point cage for my 69 camaro

open to other options

[Blake Foster]

not sure where you can get it but the size depends on what rules your trying to meet
NHRA for a "Roll cage" is 1 5/8 x .083 CM or .118 MS
for road racing it is more dependant on the car weigth but most likley 1 /34 x but i would double check that spec.
also if using it for NHRA it MUST be TIG welded

[deuce_454]

Originally Posted by killer69

not sure where you can get it but the size depends on what rules your trying to meet
NHRA for a "Roll cage" is 1 5/8 x .083 CM or .118 MS
for road racing it is more dependant on the car weigth but most likley 1 /34 x but i would double check that spec.
also if using it for NHRA it MUST be TIG welded

Thats funny.. if you use Chrome moly for any areospace application it must be welded with an oxy acetylene torch, or the weld must be annealed if tigged....

[Apogee]

I would personally use DOM mild steel over chromoly unless you're planning on post heat-treatment at the weld zones like duece_454 pointed out. There was a big fuss a few years ago about mandating chromoly cages in some of the SCORE desert classes which boiled down to the cost versus safety...the debate was about whether a chromoly cage is really safer than a DOM cage. Racing is an inherently unsafe activity, however nobody wants to pay more for something that doesn't definitely improve the safety of the rigs and/or give them some competitive advantage.

While there's no doubt that chromoly is stronger for the same wall thickness so long as it's welded properly, the debate centered around how rigid you wanted your cage to be? Cars have crumple zones for a reason and that's to distribute the force of an impact over a greater period of time since the impact is typically what does the most damage to the soft and squishy thing inside called the "driver". I think we can all agree though that once a crash begins to occur, the "driver" is really a passenger at that point.

Tobin

[NOT A TA]

I went through the whole cage thing a little over a year ago. Chromo Vs. DOM , sizing, and sanctioning body tech requirements. Here's a couple links to threads you might find informative. Beware of assuming that rollbars and cage structures you see in PT type cars are legal for any sanctioning bodies. Get the rulebooks for any sanctioning bodies where you might run the car.

https://lateral-g.net/forums/show...light=chromoly

http://www.pro-touring.com/forum/showthread.php?t=48151

[Blake Foster]

i have herd that the Tig om CM process is acceptable if you wrap the weld and let it cool slowly???? not that any one does it.
i think in reality to make it PERFECT you would want to heat treat the entire cage after welding, but no one is going to do that.
DOM is definatly cheaper. and the fit is not quite as critical and it can then be mig welded..

Deuce454 i know the procees is different but tig and gas welding would be esentially the same? no just that tig would be more controlable would it not?

and what is the BEST filler to use on CM if anyone can shed some light there, we use a 312 rod. only because no one sems to know what if anything is better. my fab guy has been building roadrace cars for 15 years and that is the best material he has found to date.

[mfain]

To support Killer69's point that you should check the rulebook for the type of competition you plan to participate in, I have included an excerpt from the NASA (Road Race) rule book for roll cage tubing size. The Ultimate Track Car Challenge uses the NASA rules, and the unlimited rules for the Silver State Classic are very similar. There are lots of other cage construction "rules" in this and other CCRs (SCCA, Proautosports, NHRA, etc). I've included the website for the NASA rulebook -- pages 59-64 contain NASA cage rules. Some sanctioning bodies let you use thinner wall Chrome-moly because of its strength, but NASA, for example, specifies the same wall thickness for DOM and Chrome-moly.

http://www.nasaproracing.com/rules/ccr.pdf

15.6.18 Roll Cage Tubing Sizes
For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but without fuel and driver. Note: There is an allowance of minus 0.010 inches on all tubing thicknesses. Minimum tubing size for the roll cage is:
Up to 1500 lbs.
1.375” x 0.095” Chrome-moly / Seamless mild steel (CDS or DOM)
1501 - 2500 lbs.
1.500” x 0.095” Chrome-moly / Seamless mild steel (CDS or DOM)
1.500” x 0.120” ERW* (No issuance of log books for cars with ERW cages 04/30/03)
*Note- Specifications listed for reference for inspection of grandfathered vehicles.
2501 - 3000 lbs.
1.500” x 0.120” Chrome-moly / Seamless mild steel (CDS or DOM)
1.750” x 0.095” Chrome-moly / Seamless mild steel (CDS or DOM)
1.750” x 0.120” ERW* (No issuance of log books for cars with ERW cages 04/30/03)
*Note- Specifications listed for reference for inspection of grandfathered vehicles.
3001 - 4000 lbs.
1.750” x .120” Chrome-moly / Seamless mild steel (CDS or DOM)
No ERW allowed.

[GregWeld]

4130 Chrome Moly tubing can be welded with ER70S or ER80S (stronger)... using TIG... best with a gas lens... and keeping the heat under control or you pull the carbon out. Pre and post heat are only required on .125 wall or thicker. Quenching would cause cracking.

[GregWeld]

312 SS rod -- also called "supermissle" -- EASY to weld with - wets out nice and doesn't magnetize.... good material choice for Chrome Moly tube and has a tensile strength of 120,000 which is higher than the 70 or 80 (which is 70 or 80,000 depending on the rod used as the numbers indicate).

[ccracin]

From what I recall all Nextel Cup chassis are Cold Drawn Seamless tubing.

DOM is not necessarily stronger than ERW (Electric Resistance Welded) for a given alloy. DOM (Drawn Over Mandrel) has a more consistent size and shape so that it has consistent properties in any direction for lack of a better term. DOM still does have a seam that is fused therefore you still have a heat affected zone down the length of the tube. After the tube is formed and welded, it is then pulled over a mandrel to accurately form the shape which provides a more uniform wall thickness, ID, OD. This also does some cold working and can possibly add some strength.

CDS (Cold Drawn Seamless) tubing is formed from a solid carbon steel bar by drawing it over a mandrel to form it's shape. Therefore there is no welded seam. This process also cold works the steel and improves it's mechanical properties.

Chromoly Tube is basically CDS tubing made from 4130 alloy steel. Standard CDS tube is typically 1018 or 1020 carbon steel. The 4130 alloy has greater tensile and yield strength than 1020 while maintaining good ductility. However it does require certain things be done before during and after the welding process to ensure the weld integrity as well as the quality of the base metal in the heat affected zone of the weld.

As said before, Chromoly is not lighter than CDS or DOM. Because it has better mechanical properties, you can typically use less wall thickness for a given tube than CDS or DOM.

I am not a metallurgist or welding engineer, but it is my opinion that you should not attempt to use 4130 unless you are well schooled on the requirements of properly welding this material. I have seen failures that can be attributed to not doing it properly and by people that say gee "I have done it like this for years with no problem". They just got lucky for years. I can't go into the proper procedure because frankly, I don't know it. Meaning there are different methods for different thicknesses, weld processes and weld joint configurations.

Honestly, these same considerations should be taken into account for any structural/safety related weld. I can weld, but when it comes to these types of welds I get a friend and certified professional welder to do it for me. I think it is worth it.

Well, thus ends me running off at the mouth. Don't take this as gospel just me trying to pass on some information I picked up along the way. Sorry for the book. Hope it helps.