Components are mounted on a set of optical cages that are made using a combination of fastening plates and 6-mm mild steel rods, see Fig. . The two end-plates (W, Z) and the two inner plates (X, Y) are made from aluminium composite sheeting, a rigid aluminium/ polyethylene/aluminium laminate that can be readily machined using even entry-level desktop mills. The rods are attached to the plates by means of button-headed M3 screws that project through 3-mm positioning holes in the mounting plates and screw directly into 15-mm threads tapped in the ends of each rod, see Fig. . Two additional plates (U, V) that form part of the motor assembly are 3D-printed from PLA.