I have an option to buy a roll cage made out of 1.75" mild steel. Or for about 30% more, I could get the same cage out of 2" DOM.
To be honest, I'm not sure what the letters DOM even stand for. What's the difference? Is this worth the extra price?
I'm sure thicker tubes are better, and I suspect there is something special about DOM metal that makes it stronger than non-DOM... but if the 1.75" mild steel will do the job, there's no need for overkill... is there?
DOM = drawn over mandrel.
I don't think the mild steel will provide much of benefit should you actually need to use it. That is, in a roll over, you want the roll cage to still be there when the dust settles, mild steel will not hold up.
There is no need to not overkill. This is a place where overkill might save your life. Spend the money.
Drawn Over Mandrel
DOM stands for "Drawn over Mandrel". I think the stuff starts out as bar stock, gets welded into a tube, hardened and then pulled over the mandrel ( a rod ). I can't remember if the last bit happens when hot or cold - I think cold.
Dave Milne, Scotland '99 TJ 4.0 Sahara
Depends who is in the Jeep when it rolls... td
The 2" DOM cage is offered by Essentially Off Road.
The 1 3/4" cage is offered by a local guy working out of his garage, but he has a good reputation locally.
The most important consideration you should consider is HISTORY of successful resistance to collapse in any design you choose. Ultimate tensile and yield value numbers are of SECONDARY or lower importance per se. The most probable failure mode of a roll cage will be by what an engineer would term "buckling failure". Buckling failure is prevented by using components of the "largest" cross section, using 'lots of triangle' & lots of gussets, etc. A high strength material that is not adequately supported (by triangles/gussets,etc.) will collapse just as fast if not well designed geometrically.
Without getting into the complex mathematics of buckling failure.... simply choose the design that has the HISTORY of proven service, has the largest diameter/cross section of components, has the most triangular supports/shape, socket welds for the tubing connections, support gussets, etc. Mild steel is totally OK if the design is well done, 2" is better than 1.75; 3 inch is better than 2", etc. Stay away from designs that have long unsupported spans of tubing. The more triangles and gussets, the better. Long radius curves are better than tight curves. The most important consideration vs. buckling failure is: shape and geometry.... not tensile/yield strength.
Get the HISTORY of the design!!!!
Joshua Nels> I have an option to buy a roll cage made out of 1.75" mild steel. Or
Turns out the wall thickness on the 1.75" pipes is .134, while it's only .120 for the 2" pipes, so I may be better off with the smaller ones anyway.
Of course, this says nothing about design... if I knew enough about metalworking to design my own, I wouldn't need to hire out the job in the first place. But I don't, and I have neither the cash nor the desire to personally crash test a number of designs... so I guess I'll just go with what looks and feels solid to my eye.
Actually, 2" x .120 is stronger than 1.75" x .134 given the same steel alloy and manufacturing process. It also has a larger cross section by a small percentage.
Chris
From a structural basis the 2" would be better. .... but we're splitting hairs hsre.
YES about what LOOKS good to you. Interestingly when a designer/engineer develops such a structure, if the EYE isnt satisfied - the design isnt persued .... you're definitely right on trusting your EYE !!!! :-)
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