Since they are vented discs, you have to drill from both sides, not just one. Drill just until it breaks through to the middle.
Go to Enco, Harbor Freight, Rutland, and get a cheap rotary table. You will also need a dial indicator that fits into the chuck. Put the indicator into the chuck, with the rotor visually centered on the rotab and clamped down (this should really be done on a mill, but eh). Now rotate the rotab, and mark the high point, and zero the indicator on the low point. Loosen clamps to finger tight. Tap on rotor till the indicator reads the average from high to low readings. Rezero. Spin again. You are done when you get it to about .010" max on the high-low reading. Clamp tight, and spin to make sure clamps didn't move it.
If you use a 90deg #4 center drill, you won't need a chamfer tool. Chuck the center, and position the head to the radius of the first pattern. Spin your rotab to 0 deg. Come down until the center drill dia is about .280" for 1/4 holes. Switch to 1/4 drill (HSS at a minimum, don't use "carbon steel" bullshit), and punch through. Rotate to the next position and repeat.
To get a spiral, you are going to shift your zero deg start point progressively as you go to each new track. Say you want 5 tracks, with 20 holes. Do your 18 deg rotations from zero for track one, then go up in even increments on the start point. 0, 5, 10, 15, 20 deg start points. For a more elegant look, go 0, 3, 7, 12, 18.
Measure your rotor and draw the pattern you want on CAD or graft paper before you start. Finding that your pattern won't work after you started would suck.
