Need a steel beam? You can 3D print PLA beams that are as strong as a steel beam of equivalent weight according to [RepRap]. The Python code for FreeCAD generates a repeating structure especially well suited for belt printers that can print a beam of any length. Keep in mind, of course, given two things that weigh the same, if one is made of steel and the other PLA, the steel one will be physically smaller.
The beams are repeating tetrahedrons which are quite strong with a lot of material on the outer faces to resist bending. Each beam end has a neat block with a wiring hole and a ring of small holes that allow you to mount the beams to things or each other with 30 degree increments of rotation.
Turns out, these holes are a mess for the FreeCAD geometry engine to deal with, so the script actually does what we can only call a hack. It randomly changes the size of the cut cylinders. The change is too small to be noticeable on the final print, but large enough to break the uniformity that upsets the software.
You don’t have to have a belt printer to make these beams, but if you don’t, you can only print one as long as your print bed. We wonder if we’ll start seeing 3D printers built using these beams as frame elements? It would seem to make sense.