[logfromblammo]

Fracking has solved the problem. The answer is right-angle drilling, plus the wet diamond-belt saw already used in quarries since 1984.

Drill many holes at the boundary, to the desired depth. Right-angle drill to connect the bottoms of the holes. Pull the saw through the holes to cut the sides of the block-columns. Now grab one block-column, lift it with a crane, and use the saw to make horizontal cuts at appropriate intervals to make rock blocks. Ship the blocks upstate, and use them to construct a mausoleum pyramid on your country estate. ~Or send them to your dwarven workshops to make mugs, tables, doors, and thrones.~

A rich of sufficient moxie would also cut new "local bedrock" countertops out of their own basement-quarry and tell all the other riches they know about how great it is to eat off of what used to be the floor of their very own basement, before they cut it out to make two sub-basements.

Jackhammering makes gravel. Quarrying makes usable blocks.

[sten]

~Or send them to your dwarven workshops to make mugs, tables, doors, and thrones.~

They're already rich so no need for further trade goods at this point. Best to continue to dig deeper... By the way, Dwarffortress is coming to Steam 'soon'.

[wool_gather]

Maybe I don't understand the "right angle drill" but how do you position this at the bottom of the depth you're excavating, while you're trying to excavate?

[logfromblammo]

Drill vertically to the desired depth. At the bottom of that hole, drill horizontally.

I think the idea is that rather than rotating a power-transfer shaft with a drill bit fixed on the end, you just rotate the drill bit with a "mud motor" and circulate the power-transfer fluid with a pump on the surface. The end of the hole can then proceed in any direction, and the only thing you need to feed down the hole is hydraulic pressure and more length of high-pressure hoses and perhaps data wires to control the bit assembly.

You only need a straight line if you're using the torque on a rigid shaft to transfer power. If you can get the mud-powered drill bit assembly to fit within the bore of the vertical hole, you can drill in any direction you want from the bottom of it. It drills in that direction, and pulls itself into the hole it is boring.

This is only necessary because the stone saw is essentially a cable with high tensile strength coated in tiny bits of diamond. In order to cut, you have to pull the circulating cable through the rock. It's like slicing cheese by putting the cheese on top of a wire and lifting the wire up, rather than by pushing down on it with a knife. Vertical cuts in the rock extend upward from the length of the horizontal drill holes. You are then left with square pillars separated by straight kerf-width grooves.

Now you set anchors in the top of a pillar, and use your crane to apply upward force to counteract the weight of the pillar down to the bottom. Send some decent bearings down to the bottom of the holes, and thread your saw cable down one vertical shaft, around a well-anchored bearing, around three horizontal shafts, around another bearing, and back up an adjacent vertical shaft. Cut through the bottom of the pillar. Stop pulling before you ruin your bearings.

At this point, use the crane to lift the pillar enough to get a lifting jack under it. Now you can work at the surface. Push the pillar up from below with the jack, and cut off the anchor block. Push up more, and cut off height at regular intervals. Some of your blocks will have a quarter of a drill hole on their edges, or anchor bolt holes in them, but most will be as perfect as lasers can make them.

[logfromblammo]

And it just occurred to me that if you have good cable bearings, you can anchor them to the bottom of the vertical holes and cut downward from the surface instead of upward from horizontally-drilled shafts.