I did the same construction steps in Inkscape, then used the Union tool to make the cutting outline only. I haven't actually tested it properly yet (no A3 printer at home) but the final shape is only 28cm square (not 35mm) so it will fit on A3... either that or I did something badly wrong!
Hopefully I can put artwork on the hex face before printing and have the pretty back.
Uuuuuuuummm...
Hopefully I can put artwork on the hex face before printing and have the pretty back.