So time to start on the eyes - what I like to call the 'eye-box'. Measurements were derived from the ratios I'd worked out right back at the start of the project. Eye diameter was to be about 13cm.

Pretty simple idea: First cut a length of thin cardboard (the type we already know warps all too easily), but then back it with strips of corrugated cardboard so it will curve around the edges and be flat at the top and bottom.