Here are some useful photos to understand the mirror construction process of the Helios. This is the "Spider" glued to the back of each mirror, on the ends of each spider leg is a tiny bolt which will bend the mirror (3mm can tolerate enough bending and still be strong enough not to break) into a concave shape. This is a piece of tin (8x8cm) that the mirror is glued to, with the help of a strong adhesive like polyurethane. If you don’t have a strong adhesive, only say wood glue, a piece of wood (10x10 cm) can be screwed to this piece of tin (grind off the tips of the screws that may poke through), and the mirror glued to the wood. Weaker glues won’t usually work directly on tin so adding some wood is necessary. Also roughing up the back of the mirror a bit can help. Whatever your method, it’s best to experiment a bit before gluing all 64 mirrors!