off the topic of my original post, but since bed frames have become the focus, here's my experience with them:
1. i will use them only in locations where they are not subject to fatigue or impact loading. basically, if whatever i am building is meant to bounce, wiggle, have stuff dropped on it, or otherwise move in any fashion, i won't use bed frames. my reasoning for this is that i have found bed frames to sometimes crack instead of bend when failing. i prefer a gradual failure to a catastrophic failure.
not all bed frames are the same from my experience, but if you are bored, weld two pieces that are 2-4 feet long at right angles to each other, then drive one end securely into the ground so you have an upside down "L", like for a hanging sign. now take a pipe, large stick, or other implement of destruction, and hit the horizontal angle out near the end with a large amount of force. now look at the area around the welded joint. i have found that some angles tend to crack adjacent to the weld when under impact. plain a36 angles welded in that condition would just bend. if it is just going to be a stationary support that does not take any abuse, i might use bed frame angle, providing condition #2 is also satisfied.
#2 i'll use bed frame angle only if the length and hole requirements in it can be satisfied with a torch and grinder. if i need to screw, lag, or bolt it to metal, concrete, or wood, and the hole does not have to be a precision hole, i'll just pop the holes through with a cutting torch and clean it up with a grinder. if it requires precision located and sized holes, then i figure it also requires a quality grade of steel and i won't bother using a bed frame angle. band saw blades and drill bits will very quickly cost more than new a36 angle would.
standard bed frame 1 1/4 x 1 1/4 x 1/8 angle weighs almost exactly 1 lb per foot, so you're talking about $0.50 to $1.00 per foot for new angle, depending on where you live. always make sure to buy full 20ft lengths, as most steel supply centers charge a cutting fee, or a different rate per foot if you want a short piece. i have found that most can be convinced to lop the angles in half for free at least, so you can take them home in the truck and not have to haul a two axle trailer for 100 lb. i'm 35 miles from the closest place where i can buy a good stock of light steel, so i plan ahead and couple it with a grocery run as not to waste a trip. groceries are at least 25 miles in any direction too, so it's not a wasted trip.
