On a side note, you don't even *need* a lathe or press to make an RDA.
It wouldn't be pretty, it could leak easily, but would really look DIY.
Just off the top of my mind with minimal thinking about design:
Use a piece of copper pipe as the middle, maybe 1" diamiter and 1 or 2 inches long
Buy a pipe end cap from the hardware store to use as the top cap, drill a hole in it for your drip tip
Get some washers that fit just inside of the pipe to use for the bottom, at least enough for a 1/4 inch stack of them
Stack them and drill holes through them on opposite sides to use for the negative post screws
Put screws through the holes to use as negative posts, the heads on the bottom and a nut right on top to squeeze the washers together. Flush fit would be best
Use two nuts near the tops of the screws to secure coils on the negative posts
A rubber bushing or some other type of insulator for inside of them to insulate the positive post
Drill air holes where desired.
Only things to actually think about
-the positive pin and 510 connection
-securing the bottom to the middle, was thinking screws into the side of the pipe into a hole drilled into the washers. Or if 4 holes are drilled in the sides where the washers are, buy some stiff wire (ie, cotter pin) and bend it to wrap around the middle with the ends sticking into the holes.
Ahh, a possible solution to the leaking just came to mind. If one of the washers is slightly thinner then the others in the stack, it would provide a space to put a rubber o ring around it to help prevent leaks. Could do it with two different washers to allow a larger o-ring or multiple o-rings.