In this step, we attach the back plate to the center plate. Alignment is key.
These are the two pieces involved in this step. The center plate is pretty easy to identify, but don't confuse the back plate with the front plate. The main difference is that the front plate has an opening for the LED next to the big circle part.
Apply glue liberally to the back plate. If you're using the plastruct glue, you may need to do a couple passes with the glue to get good, wet coverage.
Gently place the back plate onto the center plate, and nudge it around as necessary until it is properly aligned. Once everything is lined up, press the halves together with your fingers. The key areas to make sure are aligned are the edges of the circle, and also the arches along the arms. If you've got those three points aligned, you should be golden.
In case your glue dried before you had a chance to get the whole thing in place, you can lift up an edge using an exacto blade, then brush some glue onto the inside of the back plate. Don't be sloppy!
Once the glue has dried, I recommend doing a light sanding of the surface to remove any glue you may have gotten on it. Don't worry too much about the edges just yet. Just make sure it's clean.
I did a little bit of sanding here, but didn't go out of my way to make sure everything was flush. I've still got a few layers to glue on, and that could change the dynamics of the edges, meaning more sanding.