Bed frames are made from spring steel, and don't weld very well. I use .090 wall tubing 1.5" diameter for all my cages (.083 wall on the really light weight machines). Tubing requires a special bender as a pipe bender will just crush it. Tubing is measured by it's O.D. and Wall thickness. Pipe is measured by the I.D. so schedule 40 1.5" pipe will be almost 1 3/4 OD. Pipe is strong, cheap, and a bender for it is much cheaper. Only real downfall versus tubing is that it is much heavier.
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