The third section is seen here clamped in position. It is an odd thickness of 21.6mm which was necessary to get the overall height and clearance under the platter correct, I made this by gluing an 18mm and a 3.6mm sheet together. This combined thickness then had a hole cut through using a router before being glued and clamped into position.
Before adding the third section I routed a hole for the bearing and a slot which has round over edges both sides and is for cable entry.