I recently acquired a small milling machine for the shop, and started in on two acrylic plates for the collar, based on a design by Tom Wisnionski. I mounted a 6" rotary table on the mill table, with a dividing plate. Starting with a rough cut circle of 1/2" acrylic, I used a 3/4" 4-flute end mill to round down the circle to 15". Next, I changed to a 1/4" 2-flute end mill to cut a circular slot 1" in from the edge. Finally, I used the dividing plate on the rotary table to advance the table by 3-1/3 degrees to cut each of the 108 slots around the perimeter. My rotary table is geared 72:1, so each turn of the crank is 5 degrees. 360 degrees divided by 108 slots equals 3-1/3 degrees per slot. It works out to 2/3 of a rotation of the crank, so I used the 39 hole circle on the dividing plate.
To finish off the lower plate, I used a 1/2" 2-flute end mill to cut an 8" circle in the center, to accomodate an 8" acrylic tube which will connect the upper and lower plates. The upper plate was made the same way, with a 12" diameter and an 11" circular slot. It was a lot trickier to cut the slots on the upper plate, because the remaining fins are very narrow. I only snapped one off though, and replaced it with a piece from a practice plate.
For the turntable connecting the collar to the radar section, I opted for the Lee Valley 9" model. As soon as I get the first couple of ribs made, I'll cut the 8" tube to connect the two plates.