Quarry

A quarry is a buildcraft mechanism that will mine a 9x9 square down to bedrock. (11x11 counting frame) To power the quarry at a reasonable speed you would want to think of setting up 2 steam engines powering it. (this is relativly slow I use 4) Something to keep in mind though is that if you use a steam engine hooked directly to the quarry you want to at a maximum pu in 1 stack of coal after each engine finishes that stack wait 5 minutes to avoid explosion. If you wanted to be really efficient you could set up a grid of redstone engines connected by conductivity pipes thus not usong coal. And remember quarries stop when they hit lava so ots a good idea to flood the quarry hole which also allows you to collect obsidian