For the advanced student of Dwarven Physics.
The wiki makes it sound like no one's done this before, which seems kind of odd, since it seems like generating free adamantine would be an incredibly attractive prospect. The basic design of the main part of the generator is this:
∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
∙++++@∙+++++++++
∙+∙∙∙┼∙+++++++++++++++
∙+∙g∙┼∙++++++++++++++@
∙+∙∙∙┼∙+++++++++++++++
∙+++++∙+++++++++
∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
The @ at the right is a stack of Marksdwarves (all in different squads so that they'll stand on the same tile) with adamantine bolts. The @ at the left is a single Perfectly Agile soldier with orders to patrol up and down, with little delays at the top and bottom. The "g" at the left is a goblin standing on a pillar (I pitted it from the z-level above.)
When the dwarf at the left runs up or down the line of doors, it opens all of them, and some of the marksdwarves shoot their bolts. By the time the bolts get there, the doors have closed, so they hit the doors and fall into the channel, where they can be collected and melted separately. (That distance is exact, by the way. Any less and they sometimes get shots through the doors, which kills your goblin. Also, with less-skilled marksdwarves, some of the bolts will stray and land on the floors, but that isn't enough to worry about even with mere dabblers.) Naturally, this is also an excellent way to train marksdwarves.
Due to a well-known theoretical model of Dwarven physics, a stack of 25 bolts can be forged from a single wafer, but 25 individual bolts can be melted down into 2.5 wafers.
I'm thinking of building some adamantine block towers to celebrate this achievement.