In short, I intend to create a device in Dwarf Fortress which, once constructed, will allow me to create arbitrary structures of a certain area out of obsidian. Ideally this could be used to do things like build labyrinths/towers/etc without wasting miners' or masons' time, and with no chance of trapped/crushed dwarves.
I have a couple of basic design ideas, and before I decide which to go with, I just have a couple questions about caveins. If I get no answers for a few days, I'll stop being lazy and figure it out myself.
First: If water and magma are mixed to form obsidian on a tile which is on top of a (currently extended) bridge and that tile is surrounded by tiles which are empty apart from the bridge, will the obsidian fall when the bridge is retracted?
Next: How about if you replace 'bridge' with 'hatch cover' or similar?
Penultimately: Can bridges be built, supported by nothing but other bridges?
Corollary: If this is done, and one bridge supporting another is retracted, will the other bridge fall?
Finally: If magma is falling vertically in some area, forming a pillar as it were, and water is sent flowing down a construction so that it falls off the construction in exactly the same place as the magma is, will the resulting obsidian fall or be stuck to the construction?
Here's what I've decided on so far for sure:
The main controller for the device will be a couple of large arrays of levers. A lever being pulled means that an equivalent spot in the final area will be filled in with a wall, in the first array, floor in the second array. Either I'll do one floor of the structure at a time, or I'll have multiple floors of the array (With each meant to build one floor of the final structure). It will make everything by casting in obsidian in successive layers. Unfortunately, stairs and ramps are impossible using this method, as well as unsupported floors, but I can think of no automated method which could do better.
I intend to start with a very simple, 4x4x2 assembler, just to test the principle. Once I've got that figured out, I'll try larger structures, and maybe try to figure out some sort of water based substitute for stairs. I can't think of any way to do it, but it would be great if I could somehow move the structure out of the 'casting area', either by dropping it or by setting up some kind of system to move the water and magma around easily.
Thoughts? Answers? Questions? Concerns?