Heat sink plan

Any machinists out there? I've got what I think is one hell of a plan, and I'm all out of lathes. Grab yourself a chunk of alumium 3" or so tall, and the same diameter of the fan you intend to use. Machine 4 threads slightly less than .25 inches thick spaced 90 degrees apart at about .75 to 1 thread per inch. I'd think that making the depth of the thread deeper at the top, and work your way down to the size of the CPU core or slightly larger would work best. Wrap with aluminum foil down to 1" from the bottom, and toss a fan on top. I'd go with draw as opposed to blow so the foil stays in place. Think about it, the air would be in contact with the heat sink for about 4 times as long, but overall flow wouldn't be reduced.
Comments, suggestions?
-Ben