1. Start with a 1/4" thick blank of aluminum
2. Cut it down to size using your router and guide bushing. This will give you the length and width you need to cut out your blade.
3. Now you can go ahead and make your first pass on your blade using a 1/4" straight bit in your router table. Use a slow speed when cutting so as not to tear up the aluminum too much and make it dull too fast.
4. Make sure to use some type of urethane coated abrasive material for this step so that when you sand off the excess material after polishing the blade edge, there won't be any scratches in it from the abrasive grains being rubbed across itself during sanding!
cnc turn blade with 1 4 shank