Spacecraft . box truss assembly Posted on December 1, 2015December 5, 2015 by dkoa tack weld outer frame of 2d truss in jig then use spacer to precisely set out 1in flat bar lengths. tack weld 1in flat bar lengths either side to 2d truss frame. on flat and level ground surface, weld pair of 2d trusses together with 1-1/2in angle bar at top and bottom corners. Finally, weld diagonal struts for cross-bracing.