A cutterhead is a large wheel-shaped device mounted on the front end of a tunneling excavation machine or tunnel boring machine that cuts through rock and soft ground. When operated, the cutterhead rotates with a lot of power and force to cut away at rock. The cutterhead is usually attached to the main body or shield of a tunnel boring machine using specially designed bearings. The motor that rotates the cutterhead is located directly inside the shield. Also located within the shield, is the thrust cylinder that supplies the forward thrust on the cutting discs. Hydraulic cylinders force the cutter discs into the rock face; the harder the rock, the more thrust is needed to break or fragment it.
A cutter head can also be referred to as tool or set of tools on a support of some type used to excavate or bore into a rock face. A cutter head usually refers to more than one or numerous cutters.