good point. what about using a diamond dremel bit, a rather large one, and inseriting it into the hole, and jiggling it around at certain spots (not bring it up all at once, as that would make grooves parallel with water)?
i think the spring idea is a good one, but what kind of flow restriction does that give?
what about using something corrosive to copper, and letting it sit in the channels for a said time, causing pits to be eaten away. would be hard to control
just throwing out ideas.
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