> Hello, made my first pinhole from aluminum pie tin, but I need to thin =
> the material some more. Sanded with 600 wet/dry paper, but have a better =
> idea: using fine grit and a marble, a "concave" surface could be =
> formed... hopefully at it's thinnest near the pinhole. Anyone tried =
> similar method? I'm trying to find a source for the grit (like is used =
> to grind glass) and hopefully don't have to mail order. Any suggestions =
> for where to find this stuff locally?
The classic technique is to make a shallow dimple in the material then
sand it down from the back to make a thin spot in a thicker sheet. Then
drill the pinhole in the thin spot.
