Tunnel Bore

The Tunnel Bore is an automatic miner from the Railcraft mod. This miner, when set up properly, will dig 3x3 tunnels in whichever direction it is facing. It is powered by solid fuels, and requires tracks to move forward. If you supply it with tracks, it will automatically place them. As well as automatically placing tracks, it will also automatically place gravel if there is not a spot to place the tracks, assuming you have given the Tunnel Bore enough gravel. It will not place gravel if the hole is over 10 blocks deep. The Tunnel Bore requires one of the three Bore Heads, Diamond Bore Head, Steel Bore Head, or an Iron Bore Head. Each Bore Head can mine the blocks that that specific tier of pickaxe can mine. For example, only Diamond can mine Obsidian. The Tunnel Bore can stop for several reasons; the Bore Head has broken, it has run out of fuel, tracks, or gravel, there is a hole greater than 10 blocks deep, water is encountered, lava is suspected, or an unbreakable block is in it's path.

Usage
Place the Tunnel Bore in the direction you want to mine; it has to be placed on existing tracks. You will know it is facing the correct direction if the larger end is facing the way you want. Open the GUI, you will see four sections, "Head", "Fuel", "Ballast", and "Track". Place your desired Bore Head in the Head slot. Place a sufficient amount of solid fuel in the Fuel slot. Place gravel in the Ballast slot, and place tracks in the Track slots. The Tunnel Bore will not store blocks it breaks, they will simply pop out the back and land on whatever is behind it. To store the items, link one or several Chest Carts to the Bore using a Crowbar. You can also store fuel, gravel, tracks, and bore heads in the linked carts; the bore will automatically restock itself with the items in the carts.