I found that .002" brass shimstock works cleaner than aluminum. Don't try to make the hole the finished size in one step. Instead, insert the needle a short distance through the material, sand down the bur, and repeat this until the desired size is reached. If any burr remains, a needle with the tip ground to about a 45 degree cone can be rotated in the pinhole to abrade away the burr. Pinholes the size of yours can be drilled with a no. 74 or 75 drill, perhaps obtainable at a hobby or model shop. A small pin vise is handy for holding the drill, needles, and other pinhole making tools. When using a drill, clamp the material between sheets of fairly hard material to reduce burrs. There is much information on making pinhole cameras and doing pinhole photography at http://www.f295.org/Pinholeforum/forum/Blah.pl.