Mild steel angle bar is liable to twist or bend before the truss is triangulated; to ensure that each octet truss you make is straight (±1 mm) use a straight and square metal jig with wood board forming welding bed (will burn over time, flip over before replacing). Use clamps to secure 2d truss frame to jig, and push metal against wood plate of jig with a nonconductive pipe or wood stick.
Welding: Tack weld first throughout to assemble octet truss, then complete full weld once all metal elements are held in contact. Usually a small amount of grinding required to clear sharp edges. Apply hardener coat to seal and spray 3-6 coats of automotive paint. Paint damage possible (e.g. scratches) during transport and assembly; paint touch-up work may be done after assembly.
This was the first time we welded a complete full-length octet truss. Rudimentary structural tests after fabrication demonstrated good performance/strength but unacceptable dimensional tolerance (i.e. it was strong, but not precise).
Special thanks to Chamil, master maker at the Kokrobitey Institute makerspace, who suggested to develop a 2d truss jig (to hold 1in angle bar frame straight and square while welding) and square pyramid jig (to enable standardized production welding of square pyramids, as a component for full octet truss).