The Black Thunder coal mine in the Powder River Basin in Wyoming, US, is the fifth largest coal mine by reserve. The surface mine spread across an area of 35,700 acres was estimated to contain 1,466.1Mt of recoverable coal reserve as of December 2012. It is owned and operated by Arch Coal.
The fourth category covers modern machine tools and processes for machining ultrahard metals not machinable by older methods. 1  Machine tools that form parts by removing metal chips from a workpiece include lathes, shapers and planers, drilling machines, milling machines, grinders, and power saws.
Rotating abrasive wheel on a bench grinder. Pedal-powered grinding machine, Russia, 1902. A grinding machine, often shortened to grinder, is any of various power tools or machine tools used for grinding, which is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.