Attaching circuit boards to form 3D Shape
CNC or 3d Printed connecting shields. For normal use, you would make one piece where the boards slot into place, but there would be slight gaps, depending on the design. For gapless use, you need to make them in two pieces. One for the frontside, one for the backside, on each corner. Designed to meet the angle you want. There would be x number of holes, one for each pcb that is meant to join at that corner. A hole would also be made in the pcb. Then you screw or bolt them together.
Think box corner protectors. 
Heck, you could even get them stamped or cut out of metal, if you want the gapless ones.