So I'm finally ready on my current map to start playing with some Adamantine, but there's a problem with that plan; the topmost part is still in the magma ocean, and at most I'd be able to get 4 units per level, assuming I don't hit HFS first. It would be much safer to mine the outer edges, but being surrounded with magma makes this impossible, at the moment.
Too stubborn Dwarvenly to give up, I came up a plan to gain access to the submerged pillar; Drop gigantic walls of stone into key positions around the pillar, and then pump the isolated magma region out. Sounded like it would work. So I picked the first point to be cut off, a roughly 10 unit long section that needed to be 3 z levels high to reach from the Semi-Molten Rock to the top of the magma ocean. After cutting out this shape directly above, killing 3 FB's that I let accumulate in the cavern, and drop it in, there was plenty of dust and magma mist (It looked tasty.), but the giant floodgate had disappeared.
Then I realized that items weren't the only things to disappear when dropped on SMR. Angrily, I start over, this time building grooves into the side of the piece, so that at the same time the wall reached the bottom of the magma ocean the teeth/grooves will not be able to fall down anymore, giving the wall a max falling distance. Fricken clever, I thought. After I screw up once, I get the giant piece of solid rock correct and drop it in. Despite sacrificing a crippled engineer, it still failed, the teeth designed to catch on a ledge having done so, but the rest of the wall continued on it's way down into SMR.
Anyone else have any good ways of draining sections of the Magma Ocean? I'm going to try doing it stepwise this time, by casting obsidian one level at a time, pumping out the magma bubble I isolate, and repeat.