With the eye assembly finished, the full assembly follows.

The eye assembly attaches to the skull with M3 screws at two points. One goes vertically into a screw hole in the bottom of the skull and the other goes horizontally in the top. These need to be at least 12mm long but other sizes might do the trick.

The jaw assembly has a bracket (part 4 in the diagram) with a cylindrical post on the right side and a servo mount on the left. This lets you snap the jaw into place once the disc horn (part 7) is screwed into the jaw. It's easiest to attach the jaw to the bracket first, then screw it into the skull. These screws should also be about 12mm long.

The side panels attach with M6 screws for aesthetic reasons (the original bastion has big screws in these locations). The eye trim attaches to the skull with two screws through the top. The tolerances are pretty tight here, so make sure the features are cleaned really well.

The neck bracket slides into a pocket in the back of the skull vertically and two M3 screws fasten it in place. The screw caps (part 10) are optional, but they make the piece look a bit cleaner.

The neck swivel bracket (14) has a hole that the bearing gear (15) fits into with some play so it can move freely. If printed accurately, the bearing gear will press fit into place in the bottom of the neck bracket (13) without the need for glue. The bearing (16) press fits into the bearing gear (15) and onto a hollow post inside the neck piece. This allows you to feed the cable from the servo (6) through the neck, bearing, and neck bracket. The neck swivel bracket attaches to the neck with m3 screws, and the neck arms (18) glue into place on the sides of the neck. The end caps are an extra touch to add a little contrast to the piece.

Theres a driver gear (not shown in the diagram) that screws into the servo post and interfaces with the bearing gear to make the head turn.

The neck arms (18) screw into the base with M3 screws through the bottom and a hose bib (20) takes the mesh tube with the servo cables inside it and the 3mm silicon tube that's just there for aesthetic reasons.

That's it, the whole head is assembled! Now all that's left to do is assemble the controller and put everything in place.