The only difference between regular tubing and DOM is the inside diameter is more accurate for tapping the 5/8 threads. It is not that much more expensive but regular tubing is just as strong.
Regular tubing has a welded seam. DOM is "drawn over mandrel" and is stronger. Probably be a Good idea to use dom. Pick it up at jets or summit or speedway. By the foot. ford for life
DOM has a welded seam, just like ERW. In the case of DOM, it is a seam that has been smoothed out by a mandrel, after welding. It is more unform in grain and dimension, and a fair amount stronger.
There's a few more differences than that. Here is what the Steel Tube Institute of North America has to say about DOM: The DOM Manufacturing Process The manufacturing process for DOM tubing begins with coils of steel, which are slit to the proper width for the desired tube size. The strip is cold formed and passed through an electric resistance welder which joins the edges together, under pressure, to complete the tubular shape. After testing the weld's integrity, the tubing is cut to length for further processing. The cold-drawing process creates a uniform, precision product with substantially improved tolerances, surface finish and tensile strength, increased hardness and good machinability. In this process, the tube is cleaned and annealed, and one end of each length is squeezed to a point so it can be gripped by the drawing mechanism. The tube is then drawn through one or more dies and over mandrels. This reduces the diameter of the tube and thins its walls to the required dimensions in a controlled fashion to provide the qualities desired in the finished product. Metallurgically, drawing improves the tube's concentricity, tensile strength, hardness and machinability. Close dimensional accuracy is achieved through tight control of both outside and inside diameters.
not needed for shop built ladder bars ---all the special qualities are for conformity in a manufacturing process...
It depends how heavy or light you want to make them for a given strength. DOM is slightly stronger, so they can be made a little lighter than ERW. Chrome moly is stronger than mild steel, so can be made lighter yet.
Chrome moly not recommended. It has problems with breaking next to the welds unless heat treated. Mild steel is safer, easier to work with and will bend easier in an accident. Race car builders tried chrome moly years ago and went back to steel. A little heavier but you know where you are.
for a fully triangulated structure the failure would likely be buckling of some straight section, and the basic formulas for the critical buckling load don't take material tensile strength into account. Just the "modulus of elasticity" or "E" https://www.efunda.com/formulae/solid_mechanics/columns/columns.cfm And "E" is essentially the same (~ 30,000,000 psi ) for all steel no matter what alloy or heat treatment. http://www.engineersedge.com/manufacturing_spec/properties_of_metals_strength.htm In the buckling formulas "I" is also very important. That is related mostly to tube diameter, and to a lesser degree wall thickness. If the ladder bar is NOT fully triangulated then the bending strength of the tube is important. Again big diameter is more powerful than exotic material. And details of the joint and gusset design can REALLY make a difference.
Back in the '60s we built ladder bars out of thick walled square stock with threaded bungs in the ends and lots of bracing. They were heavy and welded with an AC crackerbox and 6011 rods. I don't remember ever breaking one. If you have access to better stuff then use it but it isn't a show stopper.
dom is also good for roll cages. it has a minimum wall thickness rating. it will always pass a sonic check.
I've bought several roll bar kits from Chris Alston's Chassisworks, none of them were DOM. Neather are the ones that get bent up anywhere around here. Sure DOM is better, but not in the rulebook for cages.
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